Jumat, 22 Juli 2011

Hi-Fi



- - - LPF DC Operating Point ---
V(supply): 6 V
V(out): 2.0419 V
V(d): 5.35688 V
Ic(Q5): -0.645428 mA
Id(J1): 1.04209 mA

The audio filter circuit that I designed in did not use the notch but is an S-K (Sallen-Key) 3 pole design. It could be tweaked a bit for the European station spacing, but is probably okay without any design change as it is. The filter compromise reduces noise at the expense of bandwidth. Most cheap radios have inadequate filtering, erring on the side of too much in the case of AM tuners (about 3KHz. roll off) to too little in the case of cheap radios. I erred on the side of (perhaps) too little, in order to include more bandwidth so that the audio upper spectrum would be present if broadcast. I'm relying on the sharper cutoff of a 3-pole Chebyshev filter to help more with noise while allowing "flat" (has some peaking) response to 6.6KHz. Listening revealed that I could get a little more by allowing 10KHz. bandwidth, but the noise was much more noticeable. The chosen bandwidth works with the 9KHz. European. channel spacing as well.
Note that I used a BF244B FET in the circuit, but a 2N4416 for the simulation. The two devices have very close to the same characteristics. Also, the filter works just about as well
with some standard components for C4 and C2. Here are the new values:
C4 old=15nF, new=10nF
C2 old=39nF, new=33nF
The resulting filter response looks very much the same, but the filter gains some bandwidth. These parts are easier to get, but 5% tolerance would be advised for C2, C3, and C4.
I later discovered that the JFET-BJT follower circuit works better when the drain resistor (R14 in the simulation, R18 on the full schematic) is increased to 1K ohm. I made this change when I found that one of my circuits had more distortion than expected. The FETs have a lot of variation, and increasing the resistor value makes the circuit more tolerant over the full range of possible BF244B FET characteristics.

I have to say that this tuner gives me "near FM" quality on AM. The few distractions come from static which AM is famous for, and can't be eliminated, but other than this, it sounds
great.




Here is a Hi-Fi AM superhet receiver using the linear detector discussed above. The whole thing fits on a small PC board pictured right. The linear detector is on the part of the PC board in the foreground, and the TO220 package to the left of it is an LM317 voltage regulator for the 6V power rail.
The front end circuit is shown below. It uses the NXP / Philips NE602 double-balanced mixer chip; or, as here, the SA612, which is a lower cost version.

C5 and C6 were NOT fitted in the final build. The NE602 / SA612 has differential input and output, but I wanted the option of running single ended in case the ground would help. The filter formed by the 21.5 ohm resistor and 10uH choke keeps feedback from occurring through the power supply rail, which will cause the receiver to oscillate if those components are not present. C17 is part of that filter too. The oscillator coil was used "inverted" from what is normal. The tap is closest to the "hot" end of the coil, since the SA612 oscillator doesn't need much "step-up" from the transformer. In fact, the resistor is to reduce the drive somewhat, to keep the oscillator amplitude from being too much.
To avoid stability problems, the "loopstick" antenna should preferably be shielded from the rest of the circuit. Placing the circuit in a metal box, with the loop antenna outside is optimum. My implementation had the loop antenna attached to the PC board, which allows some feedback through the receiver of the 455KHz. signal and hence some "tweet".
The IF amplifier is shown on the complete Circuit Schematic (GIF image, click to open it in a separate browser window) and is discussed in more detail later. Note that the Toko IF transformers have an internal resonating capacitor, which is not shown on the diagrams. The detector and audio output part of the circuit is shown below.

Q7, Q5, Q6, and Q8 comprise the detector circuit. Q9 and Q10 form a unity gain buffer, and 3-pole active low pass filter that cuts off at 7KHz. (12 dB down at 10KHz.). Q9 is a BF244B
N channel JFET. The IF amplifier has AGC driven by the detector output at the top of R16.
READ MORE - Hi-Fi

DDS AD9851




DDS AD9851 for the HF + 6M Transceiver Radio

Direct Digital Synthesis (DDS) is a frequency generator with digital synthesis using a reference clock. The principle is no different from the PLL (phase locked loop), only the PLL uses a VCO to generate the frekewensi. In other words DDS = digital PLL.
DDS has been widely applied to radio transceiver, especially at the low end segment of the factory transceiver. Medium segment of mid and high end, still using the PLL, with consideration, for now the PLL is still better than DDS.
DDS uses firmware homebrew made by CV.Niras (VU3CNS) with some modifications on the hardware. In this project I use the AD9851. AD9850 can also be used, but the 6x multiplier it should be disabled, and use max 120MHz reference clock.

Specifications:
1. Using the AD9851 and 2x 16F628A
2. 25MHz reference clock, 6x multiplier
3. Generating frequency from 0-60Mhz
4. Having VFO-A, VFO-B, and RIT
5. 20 programs have memory to store the VFO-A and VFO-B
6. Mode control has a LSB, USB, CW, and AM
7. Having control for BPF and LPF for the entire nine HF bands (160m, 80m, ...., 10m)
8. Input data using a mechanical encoder and numeric pad.
9. Has 6 control buttons Save / Memory, Split / VFO A = B / RIT, Lock / Mode, Step, and Calibration
10. RF output is around 20mW (MAV-11)
11. Display frequency: direct, LO-IF, or IF-LO.

Aside from being a Local oscillator in radio communications, DDS is also used as signal generators, function generators, etc..
DDS IC soldering into the PCB requires precision and patience are very high. It is small and the distance between the feet is very tight. I failed 3 times already, which means I lost 3 pieces of PCB and 3 IC DDS, mahaaal experience.
To make it easier for soldering, and assemble his DDS IC, I bought a 28 pin SOIC to DIL adapter PCB (U.S. $ 2 + ongkir), and re-designing its layout pcb with 28 pin DIL.
Since the AD9851 output signal is only 0.5mW, and I plug 60Mhz LPF and MAV-11 amplifier. Signal is strong enough, and enough to drive the diode mixer level 7 or 10.
READ MORE - DDS AD9851

Kamis, 21 Juli 2011

Hi-Fi audio


Hi-Fi audio
This circuit is a simple audio amplifier based on TDA1910 IC. This circuit will deliver 10W power output if used 8 ohm loudspeaker and powered with 24V DC supply.
Note

* Use 18-24V DC for powering the circuit.
* A proper heat sink is necessary for the IC.

The TDA 1910 IC is a monolithic integrated circuit inmultiwatt package, intended for use in Hi-Fi audio power applications, as high quality TV sets. The TDA 1910 meets the DIN 45500 (d = 0.5%) guaranteed output power of 10W when used at 24V/4W. At 24V/8W the output power is 7W min.

Maximun ratings TDA 1910 IC
* Supply voltage 30 V
* Output peak current (non repetitive) 3.5 A
* Io Output peak current (repetitive) 3.0 A
* Input voltage 0 to + Vs V
* Differential input voltage ± 7 V
* Power dissipation at Tcase = 90°C 2 0W
* Storage and junction temperature -40 to 150 °
READ MORE - Hi-Fi audio

PIR




A normal electronic security system will have a transmitter and a receiver. The transmitter sends out an IR laser and this will be received by the receiver. When an intruder walks past the device, the IR beam is cut and thus the alarm is activated. But, this system has some major disadvantages like limited range and poor line of sight. These disadvantages are eliminated through the PIR sensor circuit explained below.
Working

Instead of infrared or laser transmitters and receivers, PIR (Passive Infrared Radial) sensors are used in this circuit. The sensor is basically a pyroelectric device. When the device is exposed to infrared radiation, it generates an electric charge. The device is made of crystalline material. According to the change in the amount of infrared striking the element, there will be a change in the voltages generated, which is measured by an on-board amplifier.

The infrared light explained here refers to the light radiating from all objects in its field of view. The reason for not having a transmitter and receiver is that the device does not emit one, but only accepts the energy emitted from objects above absolute zero in the form of radiations. Thus the temperature will be different for a human working past a sensor, and that of a wall right in front of it. Thus the word “passive” is used in PIR to explain that it does not emit a radiation and receive it, but instead accepts the incoming infrared radiation passively.
READ MORE - PIR

audio power


TDA2009 is an audio power amplifier double hi-fi in multiwatt package, especially developed for applications of high quality stereo. That application is the amplification in bridge, where it is used the two amplifiers interns of the tda2009. The good of the series of circuits integrated tda is that are component electronic easy to find at the electronics stores. Although some can find the potency of 18 watts little rms, be sure that many of those audio equipments industrialized they use that type of integrated circuit and they speak in potencies of up to 100 watts. That circuit supplies a potency even considerable to hear music.
READ MORE - audio power

Jumat, 15 Juli 2011

LM2575



The switching regulator power supply used LM2575-5.0 on this schematic. You can make the stable voltage by using the 3 terminal regulator like LM317. However, because the output electric current and the inputted electric current are the same approximately, the difference between the input electric power (The input voltage x The input electric current) and the output power (The output voltage x The output current) is consumed as the heat with the regulator. Because it is, the efficiency isnt good.

The LM2575 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 1A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V, 15V, and an adjustable output version.

Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation and a fixed-frequency oscillator.

The LM2575 series offers a high-efficiency replacement for popular three-terminal linear regulators. It substantially reduces the size of the heat sink, and in many cases no heat sink is required.
READ MORE - LM2575

ZN414 IC



At this point it is worthwhile downloading the data sheets. Search for data on not just the ZN414, but the other clones as well.
One of the Ferranti sheets is available here on the Jaycar site.
Briefly, the tuned circuit is fed straight into the IC. There is no need for a tapped coil due to the 4M input impedance. Looking at the internal diagram of the TA7642, we can see this is a result of using an emitter follower at the input pin. Four stages of amplification and an active detector result in a gain of about 72dB which is high enough to give good results with no external aerial. In fact, gain is not too far off an average superhet using the same size aerial rod. The .1uF at the output pin is for RF bypassing, and in conjunction with Ragc, determines the audio bandwidth. The data sheet shows how this capacitor value is calculated. Apparently, the higher the value, the more gain can be had. This would make sense as RF bypassing would be improved with an increase in capacitance value.
The DC at the output pin varies with signal strength and this is used for AGC. The 100K and .01uF are the usual time constant to remove audio fluctuations. In addition, the .01uF is also the RF bypass for the earthy end of the aerial coil and tuning condenser. Gain of the IC is thus controlled by the DC at the input pin.
I have seen some circuits incorrectly drawn, particularly with the LMF501T clone, where the 100K has been connected directly to the input pin, along with the .01uF for DC isolation of the aerial coil. While it would work to a degree, and the DC conditions are correct, the problem is 100K is effectively shunted across the aerial coil and will result in loss of gain and selectivity.
It is important that the tuned circuit is the only thing connected to the input pin.

My interest had been rekindled of late as Dick Smith was selling MK484's at half price. Knowing that they are slowly getting rid of components, I went and stocked up with a lifetime supply. I have known about the ZN414 for years; for a long time the Dick Smith catalog had provided a circuit (EA May 1974) in the back of their catalog.
The ads for the device proclaimed such virtues as "equivalent to a ten transistor radio". Ten transistors it may have, but it actually has only four stages of RF amplification. This is about the practical limit before instability would set in. The other transistors are used for the detector, AGC, impedance matching, and stabilisation.

The first time I actually used the ZN414 was with the Funway kits back in 1981. In the Funway 1 volume was the "Beer Powered Radio" which was the standard ZN414 circuit driving a crystal earphone but powered from a homemade battery using beer as the electrolyte. A modification was shown to run the circuit from a 9V battery instead, which needless to say is the version I built. In Funway 2 was the "Pocket Transistor Radio" which drove a magnetic earphone and ran off a 9V battery. Its performance was very poor for two reasons. Firstly the method of obtaining the supply for the ZN414 was a bodge and resulted in instability, and secondly, the 9V battery pressed up against the ferrite rod ruined the signal pickup. This particular circuit was the same as EA's August 1979 design, except for the modification for 9V operation.

During the mid to late 80's when I was learning about solid state, I experimented with many different ZN414 circuits and associated audio amplifiers. I used to demonstrate to some of my fellow students a ZN414 receiver with a two transistor amplifier driving a speaker that I'd build on a breadboard from time to time. I recall listening to 2SM during one of our programming classes on such a set. Soon after, I went off listening to AM as a results of changes to formats and stations migrating to FM. So, the ZN414 became dormant in my designs until recently, now that I'm mainly listening to AM again.
Also was the fact I'd accumulated a few of the $2 shop radios using the ZN414 clones.

An AM portable radio receiver made from the ZN414 IC. The ZN414 ic has now been replaced by the MK484 which is identical in performance and pinout.

Notes:
Designed around the popular ZN414 IC this receiver covers the medium wave band band from approximately 550 to 1600 KHz with the values shown. The coil and tuning capacitor may be taken from an old MW radio to save time. The ZN414 IC, has now been replaced by the MK484. The integrated circuit is a 3 pin, tuned radio frequency circuit, and incorporates several RF stages, automatic gain control and an AM detector. It is easily overloaded and the operating voltage of th IC is somewhat critical to achieve good results.

In this circuit a small voltage regulator is built around the BC108B transistor, four 1N4148 diodes, the 2k7 and 10k preset resistor and the 820R resistor. The 10k pot acts as a selectivity control for the whole receiver, controlling the operating voltage for the ZN414 (or MK484). If you live in an area that is permeated with strong radio signals, then the voltage may need to be decreased. I found optimum performance with a supply of around 1.2 volts.

The audio amplifier is built about an inverting 741 op-amp amplifying circuit. Extra current boost is provided using the BC109C / BC179 complementary transistor pair to drive an 8 ohm loudspeaker. The voltage gain of the complete audio amplifier is around 15. The audio output of the complete receiver is really quite good and free from distortion. I may provide a sound sample later. Click here to see a picture of my prototype. I used a small wooden enclosure and the complete tuning assembly from an old radio.
READ MORE - ZN414 IC

IC-7800


The IC-7800 uses durable mechanical relays for BPF switching instead of non-linear semi-conductors, like switching diodes which can cause distortion. The mechanical relay reduces secondary distortion at the primary stage of signal processing.

The IC-7800’s somewhat familiar looks will remind many HF operators of the IC-781. The IC-781 set benchmarks back in the 1980’s as that generation’s ultimate HF transceiver. Some of today’s operators still feel the IC-781 is the pinnacle in amateur radio design. They have not seen the IC-7800. It takes amateur radio to a whole new level of performance. The IC-7800 will be viewed as the pinnacle radio for years to come.

The IC-7800 is an artistic fusion of over 40 years analog RF circuit development expertise and cutting-edge digital technology. The result is TWO identical receivers with 110dB dynamic range, +40dBm 3rd order intercept point, and unmatched DSP technology in the HF bands something that has never been achieved in Ham radio! Simply put, Icom has developed the ultimate Amateur HF transceiver.
READ MORE - IC-7800

SCR




A rudimentary test of SCR function, or at least terminal identification, may be performed with an ohmmeter. Because the internal connection between gate and cathode is a single PN junction, a meter should indicate continuity between these terminals with the red test lead on the gate and the black test lead on the cathode like this.

All other continuity measurements performed on an SCR will show "open" ("OL" on some digital multimeter displays). It must be understood that this test is very crude and does not constitute a comprehensive assessment of the SCR. It is possible for an SCR to give good ohmmeter indications and still be defective. Ultimately, the only way to test an SCR is to subject it to a load current.

If you are using a multimeter with a "diode check" function, the gate-to-cathode junction voltage indication you get may or may not correspond to what's expected of a silicon PN junction (approximately 0.7 volts). In some cases, you will read a much lower junction voltage: mere hundredths of a volt. This is due to an internal resistor connected between the gate and cathode incorporated within some SCRs. This resistor is added to make the SCR less susceptible to false triggering by spurious voltage spikes, from circuit "noise" or from static electric discharge. In other words, having a resistor connected across the gate-cathode junction requires that a strong triggering signal (substantial current) be applied to latch the SCR. This feature is often found in larger SCRs, not on small SCRs. Bear in mind that an SCR with an internal resistor connected between gate and cathode will indicate continuity in both directions between those two terminals

If an SCR's gate is left floating (disconnected), it behaves exactly as a Shockley diode. It may be latched by breakover voltage or by exceeding the critical rate of voltage rise between anode and cathode, just as with the Shockley diode. Dropout is accomplished by reducing current until one or both internal transistors fall into cutoff mode, also like the Shockley diode. However, because the gate terminal connects directly to the base of the lower transistor, it may be used as an alternative means to latch the SCR. By applying a small voltage between gate and cathode, the lower transistor will be forced on by the resulting base current, which will cause the upper transistor to conduct, which then supplies the lower transistor's base with current so that it no longer needs to be activated by a gate voltage. The necessary gate current to initiate latch-up, of course, will be much lower than the current through the SCR from cathode to anode, so the SCR does achieve a measure of amplification.

This method of securing SCR conduction is called triggering, and it is by far the most common way that SCRs are latched in actual practice. In fact, SCRs are usually chosen so that their breakover voltage is far beyond the greatest voltage expected to be experienced from the power source, so that it can be turned on only by an intentional voltage pulse applied to the gate.
READ MORE - SCR

Selasa, 12 Juli 2011

Zener breakdown



The Zener diode is particularly interesting in the way that it operates. There are actually two mechanisms that can cause the breakdown effect that is used to provide the voltage reference effect:
Zener breakdown: Although the physics behind the effect is quite complicated, it can be considered that this effect occurs when the electric field within the semiconductor crystal lattice is sufficiently high to pull electrons out of the lattice to create a hole and electron. The electron then moves under the influence of the field to provide an electric current.


Impaction ionisation: Again this effect occurs when there is a high level of electric field. Electrons are strongly attracted and move towards the positive potential. In view of the high electric field their velocity increases, and often these high energy electrons will collide with the semiconductor lattice. When this occurs an electron may be released, leaving a hole. This newly freed electron then moves towards the positive voltage and is accelerated under the high electric field, and it to may collide with the lattice. The hole, being positively charged moves in the opposite direction to the electron. If the field is sufficiently strong sufficient numbers of collisions occur so that an effect known as avalanche breakdown occurs. This happens only when a specific field is exceeded, i.e. when a certain reverse voltage is exceeded for that diode, making it conduct in the reverse direction for a given voltage, just what is required for a voltage reference diode.

It is found that of the two effects the Zener effect predominates above about 5.5 volts whereas impact ionisation is the major effect below this voltage.

The two effects are affected by temperature variations. This means that the Zener diode voltage may vary as the temperature changes. It is found that the impact ionisation and Zener effects have temperature coefficient in opposite directions. As a result Zener diodes with reverse voltages of around 5.5 volts where the two effects occur almost equally have the most stable overall temperature coefficient as they tend to balance each other out for the optimum performance.
READ MORE - Zener breakdown

Low Drop-out



Important considerations when selecting a voltage regulator include: 1) the desired output voltage level and its regulation capability; 2) the output current capacity; 3) the applicable input voltages; 4) conversion efficiency (Pout/Pin); 5) the transient response time; 6) ease of use; and if applicable, 7) the ability to step-down or step-up output voltages. In switch-mode regulators, the switching frequency is also a consideration.

There are several types of voltage regulators, which may be classified in terms of how they operate or what type of regulation they offer. The most common regulator IC is the standard linear regulator. A typical linear voltage regulator operates by forcing a fixed voltage at the output through a voltage-controlled current source. It has a feedback mechanism that continuously adjusts the current source output based on the level of the output voltage. A drop in voltage would excite the current source into delivering more current to the load to maintain the output voltage. Thus, the capacity of this current source is generally the limiting factor for the maximum load current that the linear regulator can deliver while maintaining the required output level. The amount of time needed for the output to adjust to a change in the input or load is the transient response time of the regulator.

The feedback loop used by linear regulators need some form of compensation for stability. In most linear regulator IC's, the required feedback loop compensation is already built into the circuit, thereby requiring no external components for this purpose. However, some regulator IC's, like the low-dropout ones, do require that a capacitor be connected between the output and ground to ensure stability. The main disadvantage of linear regulators is their low efficiency, since they are constantly conducting.

The switching voltage regulator is another type of regulator IC. It differs from the linear regulator in the sense that it employs pulse width modulation (PWM) to regulate its output. The output is controlled by current that is switched at a fixed frequency ranging from a few Hz to a few kHz but with varying duty cycle. The duty cycle of the pulses increase if the output of the regulator needs to supply more load current to maintain the output voltage and decreases if the output needs to be reduced. Switching regulators are more efficient than linear regulators because they only supply power when necessary. Complexity, output ripples, and limited current capacity are the disadvantages of switching regulators.

There is also a group of regulator IC's known as Low Drop-out (LDO) regulators. The drop-out voltage is the minimum voltage across the regulator that's required to maintain the output voltage at the correct level. The lower the drop-out voltage, the less power is dissipated internally within the regulator, the higher is the regulation efficiency. In LDO regulators, the drop-out voltage is typically just about 0.6 V. Even at maximum current, the drop-out voltage increases to just about 0.7-0.8 V.
READ MORE - Low Drop-out

voltage regulator


Typically, electronic voltage regulators employ a feedback network, where a high-gain amplifier compares a fraction of the load voltage VL/k with a constant reference Vref. Any difference between these two voltages is amplified and used to control a series pass device in a manner whereby this difference is minimized. For an ideal amplifier with zero offset and infinite voltage gain, the difference is reduced to zero and the ideal relationship of Eq. (2) is realized. See also Feedback circuit.

The wide range of applications for electronic voltage regulators has led to the development of these circuits in fully monolothic integrated circuit technology, where all or most of the required circuit components are realized on a single chip of silicon. Offering various output current and voltage ratings, and output voltages of either positive or negative polarity, several commercial regulator integrated circuits are now available to suit the requirements of most applications. The designs of these regulators have matured and have become rather sophisticated. In addition to implementation of the high-gain feedback amplifier, the series pass element, and an accurate voltage reference, all on a single silicon die, built-in protection against overload conditions (such as output short circuits and excessive operating temperature) is now standard. Novel circuit-design, processing, and packaging techniques have been developed and implemented to achieve increased accuracy, temperature stability, efficiency, reliability, and power-handling capability, while reducing package size and cost. See also Integrated circuits.

Voltage regulators are used on distribution feeders to maintain voltage constant, irrespective of changes in either load current or supply voltage. Voltage variations must be minimized for the efficient operation of industrial equipment and for the satisfactory functioning of domestic appliances, television in particular. Voltage is controlled at the system generators, but this alone is inadequate because each generator supplies many feeders of diverse impedance and load characteristics. Regulators are applied either in substations to control voltage on a bus or individual feeder or on the line to reregulate the outlying portions of the system. These regulators are variable autotransformers with the primary connected across the line. The secondary, in which an adjustable voltage is induced, is connected in series with the line to boost or buck the voltage. See also Autotransformer; Electric distribution systems; Electric power substation.

Voltage regulators are used on rotating machines in power generation applications to automatically control the field excitation so as to maintain a desired machine output voltage. Rotating machines, both small (down to 1 kW) and large (up to 1,000,000 kW), are the predominant means of power generation throughout the world, and voltage regulators of varying design and sophistication are employed on most of them. Even ac generators (or alternators) in automotive applications employ voltage regulators utilizing similar principles.
READ MORE - voltage regulator

Minggu, 10 Juli 2011

How it Works and Functions Each transformer:


Understanding the transformer or transformers in brief is to energize the electromagnet components or electrical power from high voltage to low voltage or vice versa, with equal frequency. When utility power is interrupted, the officer will check the transformer is working. why transformer needed? because it usually needs a tool that does not allow the use it supply nets - nets, say so many companies are to importtechnology from outside or country of origin, say for example that Japan will open a factory in Indonesia of course technological resources ranging from machinery and other equipment should take dong because Indonesia did not have in Japan when the voltage was 110V instead of 220V was used in Indonesia like-what's the solution? step-down transformer is used of voltage 110V U.S. $ 220 used to be a simple understanding of the transformer is a device used to change the amount of voltage can be increased or scaled back
Understanding power transformer / power transformer

Power transformer is an electrical power equipment that serves to channel the energy / power from high voltage to low voltage or vice versa (transform voltage) in general terms that the power transformer
To facilitate the supervision of the operation of the transformer can be divided into: large Transformer, Trafo medium, small transformers.

How it Works and Functions Each transformer:

The main part
- The core of iron
Iron core serves to facilitate the flux path, caused by electric current through the coil. Made of thin steel plates are insulated to reduce heat (as the iron losses) caused by the "Eddy Current".
- The coil transformer

Some insulated wire wrapped to form a coil. The coil is well insulated against the iron core and to the other coil with solid insulation such as cardboard, pertinax and others. Generally there is a coil on the transformer primary and secondary. When the primary coil is connected to the voltage / alternating current in the coil then the flux that induce a voltage arises, when the secondary circuit is closed (the load circuit) then the current will flow in the coil. So the coil as a means of transformation of voltages and currents.

- The coil tertiary
Tertiary coil voltage needed to obtain a tertiary or for other needs. For both purposes, the tertiary coil is always connected to the delta. Tertiary coil is often used also for connecting auxiliary equipment such as condenser Synchrone, shunt capacitors and shunt reactors, however, not all of the power transformer has a tertiary coil.

- Transformer oil
Most of the power transformer core and coils immersed in the oil-transformer, transformer-especially large-capacity power transformer, because it has the properties of transformer oil as a heat transfer medium (circulated) and is also as insulation (high breakdown voltage power) that serves as cooling and insulation media

There are at least three causes damage to the transformer resulting in outages at the customer channel. About 30 percent are caused by the reduced volume of lubricating oil to make fast heat transformer and then burned, 24 percent due to lightning strikes, and seven percent due to excess pressure. The rest, can be caused by, for example, components that are old and should replaced and overloaded.

To overcome such defects, electrical officer will identify the cause first. If the cause is the lubricant that is reduced, we can be sure a leak on the fins, body, tap expenses, cover packing up, packing bushing and tap changer that must be patched. The officer just add oil or lubricating oil which has been reduced due to the leak until a stable size. If t / Afo damaged by lightning and overload, can be overcome by mutations transformer
READ MORE - How it Works and Functions Each transformer:

Transformer isolation and its use


isolation transformer is an isolation transformer is designed to overcome the problems associated with internal insulation to ground reference. It is built with two rolls of Faraday isolation between primary and secondary windings.

isolation transformer secondary winding having the same amount with the primary winding, so the secondary voltage is equal to the primary voltage. But in some designs, the secondary winding is made a bit more to compensate for the loss. This transformer serves as insulation between the two prop. For audio applications, the transformer of this type have been largely supplanted by the coupling capacitor.

When installed properly, insulation, closest to the primary winding, is connected to ground power supply and the isolation of the most common close to the secondary winding is connected with the isolation circuit to be isolated. The use of two shields in the construction of an isolation transformer for the transfer of high-frequency noise, which will usually be incorporated in the transformer

Both shields provide more effective isolation of primary and secondary circuits by also isolating their reasons. Transformer isolation adds the third capacitance between the two Faraday shield, which can allow high frequency noise coupling between the base system. However, increasing the separation between the two Faraday shield to minimize this capacitance is usually the third. In addition, the effect of the dielectric shield plus separation increased significantly reduce the capacitance roll-between between the rolls.

Transformer isolation and its use

isolation transformer is extensively used in medical equipment, telecommunications equipment, remote control equipment, computers & peripherals, CNC machines, analytical instruments, etc.
Losses in the transformer

Copper losses. I2.R copper losses in the windings caused by the resistance of copper and electrical currents flood.

Coupling losses. Losses incurred due to the primary-secondary coupling is not perfect, so not all the induced magnetic flux cutting the coil primary secondary. These losses can be reduced by rolling in multi-layered winding between primary and secondary.

Capacity loss is wild. Losses caused by wild capacity contained in the winding-winding transformer. These losses greatly affect the efficiency of the transformer for high frequency. These losses can be reduced by rolling the primary and secondary windings are semi-random (winding banks).

Hysteresis losses. Losses that occur when the primary AC current U-turn. Due to core transformer can not change the direction of the magnetic flux immediately. These losses can be reduced by using low reluctance core material.

Skin effect losses. As with other current-carrying conductor alternating, currents tend to flow on the surface of the conductor. This enlarges the capacity loss and also increase the relative resistance of the coil. These losses can be deducted by using Litz wire, the wire consists of several small wires are mutually insulated. For the radio frequency used geronggong wire or thin
copper sheet instead of regular wire.

Eddy current losses (currents megrim). Losses caused by emf input that causes the current in a magnetic core that is against the change of magnetic flux that generates an emf. Because of the magnetic flux is changing, there wake of magnetic flux in the core material. This loss is reduced when used multi-layer core.
READ MORE - Transformer isolation and its use

Distribution transformers and parts


The distribution transformer is a very important component in the distribution of electricity from distribution substations to consumers. Damage to the Distribution Transformer cause kontiniutas customer service will be disrupted (occurring power outages or blackouts). Blackout is a loss which causes the generation costs will increase depending on the price of unsold KWH. Selection of Distribution Transformer rating is not in accordance with the needs of the load will cause the efficiency to be small, as well as the placement location of distribution transformers are not suitable influence on the consumer end of the voltage drop or fall / voltage drop in the end of the channel / consumer.

Transformer or transformer is a component of an electromagnet that can transform high voltage to low or vice versa within the same frequency. Transformer is the heart of the distribution and transmission are expected to operate up to (work continuously without stopping). In order to function properly, eating the transformer must be maintained and cared for properly using the system and the right equipment. Transformer can be distinguished by its power, transformer 500/150 kV and 150/70 kV transformer called Interbus Transformer (IBT) and the transformer 150/20 kV and 70/20 kV distribution transformers are called. Transformers are generally grounded at the neutral point according to the need for system security or protection. For example, 150/20 kV transformer is grounded directly in the neutral 150 kV and 70/20 kV transformer is grounded by low resistance or high resistance or directly on the side of the neutral 20 kV.
Distribution transformers and parts

Parts of the distribution transformers are:
Primary winding
Secondary winding
Core

Distribution transformer serves to lower the tension 20kV medium voltage distribution transmission so that the equipment is 220/380V transformer unit (3 phase).

Some Components Distribution Transformer

1. Tertiary coil:

In addition there are several primary and secondary transformer coils are equipped with a third or tertiary winding. It is necessary to obtain tertiary voltage or for other needs.

Tertiary coil is often used also for connecting auxiliary equipment such as condenser Synchrone, shunt capacitors and shunt reactors.

2. Cooling medium:

Transformer oil should qualify them. :

a. insulation resistance (> 10kV/mm)

b. Density should be small

c. Low Viscosity

d. A high flash point, not easily evaporate who may harm

e. Not damage the insulating material at t (sifatkimia 'y)

3. Tap changer (tap changer):

Tap Changer is the change ratio of the transformer to obtain the operating voltage of the desired secondary voltage network / primary changes. The tap changer can be operated either in a state under load (on-load) or in a state unburdened (off load), depending on its type.

Distribution transformers can be mounted outside ruanga (outside installation) and can be fitted the room (fitting in) depending on the state of the load location. Maintenance is one kompanen that directly supports the reliability, power and quality of production capable of an equipment. Maintenance is not just a physical work that directly to the equipment concerned, but we need a good planning and supervision of its implementation, so that maintenance will be done regularly and in accordance with the provisions, directives applicable to the equipment concerned.
Appropriate distribution, rating according to the needs of the load will keep the voltage drop in the consumer and will increase the efficient use of distribution transformers. So the distribution transformer is one of the equipment that needs to be maintained and used as possible (as efficiently as possible), so the reliability / continuity of service to be guaranteed.
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electrical transformer and some of its components


Transformer or power transformer is a device used to convert AC line voltage, transformers made from two coils wrapped around a soft iron ring.

The coil is connected to a voltage source called the primary coil and the coil where the result is called the secondary coil. When the switch is connected, electricity flows through the primary coil and soft iron turn into a magnet.

Galvanometer needle moves a moment and go back to zero. When the switch is disconnected, the electricity stops flowing in primary coil so that the ring lost kemagnetannya, and the galvanometer needle moves back to a moment in the opposite direction.

By changing the direction of electric current continuously, then the magnetic poles will also change continuously

Electricity generated by the coil secondary coil only for a moment because this is only changing the number of lines of magnetic force when power is switched on or when power is turned off.

By connecting the primary coil to the AC power source, the electric currents are always changing, always changing the magnetic poles and coil secondary continuously changing magnetic lines of force and produce power continuously

So that the coil secondary continuously generate electricity, then he should change the magnetic lines of force continually, that is by changing the pole-pole magnets continuously
electrical transformer and some of its components:

1. Iron core
Electrical transformer iron core serves to simplify the way flux, magnetic posed by electric current through the coil. Made of thin steel plates are insulated to reduce heat (as the iron losses) generated by Eddy Current.

2. Transformer coil
Transformer coil is a few winding insulated wire forming a coil or coils. The coil consists of a primary coil and secondary coil are well insulated against the iron core and to the inter-coil with solid insulation such as cardboard, pertinak and others. The coil as a means of transformation of voltages and currents.

3. Transformer Oil
Transformer oil is one of the liquid insulating material used as insulation and coolant in the transformer.
• As part of the insulating material, the oil must have the ability to resist breakdown voltage, whereas
• as a transformer coolant oil should be capable of reducing the heat generated,
so with both the ability of the oil is expected to be able to protect the transformer from the disorder.

Electrical transformer oils have an element or compound contained hydrocarbons are paraffinic hydrocarbon compounds, hydrocarbon compounds naftenik and aromatic hydrocarbon compounds. Besides the three compounds, transformer oils still contain a compound called additives although its content is very small.

The types of equipment maintenance are as follows:
Predictive Maintenance (Conditional Maintenance) is a maintenance yangd ilakukan way to predict the condition of an electric equipment, if and when electrical equipment is likely to fail. With
predict these conditions can be known early symptoms of damage. Commonly used way is to monitor the condition of them online either at the equipment to operate or not operate. This requires equipment and
specialized personnel for analysis. Maintenance is also called maintenance based on condition (Condition Base Maintenance).

Preventive Maintenance (Time Base Maintenance)

maintenance activities are undertaken to prevent damage to the equipment suddenly and to maintain the optimum performance of equipment according to technical age. This activity is performed periodically with reference
to: Instruction Manual of the plant, the existing standards (IEC, CIGRE, etc.) and operating experience in the field. Maintenance is called
also with time-based maintenance (Time Base Maintenance).
Corrective Maintenance

is performed with planned maintenance at certain times when abnormal electrical equipment or the performance
low work function at run time in order to restore the original condition with repairs and improvements
installation. Maintenance is also called curative maintenance, which can be a trouble shooting or replacement of part / section of damaged or poorly functioning conducted with the plan.
Breakdown Maintenance

maintenance is carried out after the damage occurred suddenly that the timing is not certain and its emergencies.
Implementation of maintenance equipment can be divided into two kinds:
1. Maintenance of monitoring and carried out by operators or
patrol officer for an unattended substation (Gito - Without substation
Operators).
2. In the form of cleaning and maintenance measurements made by
maintenance officer.
READ MORE - electrical transformer and some of its components

Zener diode



For those of you who like to dwell with digital circuits, the power supply circuit above can be selected to meet your supply for digital circuits. Actually you could make with no power supply using zener diode as a voltage stabilizer. But by using a zener diode voltage of 5V at least the value that you get really 5 volts. Power supply circuit above only supports the load circuits which only requires a supply current is not so great. This is due to limitations of power dispasi zener diodes and transistors are used.

Zener diodes have the characteristics similar to an ordinary diode. When given a zener diode forward bias it will function as the wire as well as the ordinary diode. But if the ordinary diodes can not withstand the voltage at a particular value when given reverse bias on the zener diode so it can be done. Value that can be stabilized voltage varies according to the specifications of the zener diode itself. On this occasion I will not explain the working principle of the circuit power supply because you can read it on my other posts that explain the workings of the power supply or a rectifier circuit.

Components used in power supply circuit with zener diodes above are as follows:
Step Down Transformer
Diode Bridge (Kumprok) |​​ can also use regular diodes 4 pieces
Capacitors 1000 UF | The greater the value the better
Resistor 4.7 Kohm
Transistors 3904 | could also suit the needs of the other transistor
5 Volt Zener Diode


If you want to get a larger supply voltage of 5 volts then you just replace the zener diode as needed and use the ac voltage transformer keluarran a little bigger. For example to use a 9-volt zener diode, you can use an ac voltage 12 volts. See also the working principle of the rectifier, a simple power supply circuit and power supply with transformer CT.

Zener Diodes can be called Breakdown Voltage Diodes or Voltage Breakdown Diodes or Avalanche Diodes. The Zener diode has been an important component in both Voltage and Current Regulators. Prior to solid state components - a gas tube was used as a voltage regulator. Examples of gas tubes are OB2 and OB3.

There are two categories of Zener Diode. These are Voltage Breakdown Diodes and Avalanche Diodes.

The difference between the two depends on the level of doping. Voltage Breakdown Diodes operate within the region of 0 - 6 VDC. Avalanche Diodes operate within the region 5 - greater than 200 VDC. See manufacturers for the largest Zener Diode that they manufacture. Note the overlap of 1 Volt for both diodes. This overlap has been noted because the difference in action between Voltage Breakdown and Avalanche is different for every manufacturer and diode built that works in this region. If a Zener Diode is between 5 and 6 VDC then if can be described as either type.

Voltage Regulation Zener diodes are constructed to be voltage regulators, which means that they will operate at an approximate but pre-determined voltage.

They operate as a voltage regulator because they maintain a pre-determined voltage despite changes in zener current. This is only true if the current remains within the specifications engineered into the Zener.

The external circuit components must be within specifications if the Zener diode is to function properly. This is usually a single resistor.

Minimum Resistance: This resistance has a minimum value, which permits a maximum zener current, thus a maximum zener voltage. If this resistance were to reduce below this value then the zener current would burn out the diode.

Maximum Resistance: This resistance also has a maximum value, however, increasing the resistance only decreases the current, and no damage will occur to the Zener. What does happen is that the Zener no longer regulates voltage but will experience large voltage changes for minimum current changes. These voltages will be less than the minimum zener voltage and normally should not damage any associated circuitry.

Regulation: A zener diode is normally connected in parallel with the load.

If the input voltage changes, and in this example, increases, then the circuit, acting as voltage divider will see an increase in voltage across the load. This increase is also in parallel with the Zener, which because of the increase in voltage will increase Zener current. This increase in current is felt through the series resistance, dropping more voltage, thus returning the load voltage to near original value.
READ MORE - Zener diode

Sabtu, 09 Juli 2011

junction field effect transistor (JFET)



The circuit was designed to provide a means for measuring the operating voltage of zener diodes before applying on a circuit.

Zener Diode – a special kind of diode that permits the flow of current in just one or forward direction as a normal diode, but will also allow in the reverse direction if the voltage is above or larger than a certain value of the breakdown voltage
2N5363 – a low power N-channel junction field effect transistor (JFET) used for general purpose device types enclosed in a TO-72 package
Digital Voltmeter – an instrument used for measuring the potential difference between two points in an electric circuit with a special type of analog to digital converter known as integrating converter

The purpose of using Zener diodes is the due to their capability of regulating the voltage across an electric circuit. There are circuits that would require the use of Zener diodes which makes them very essential in the market. It is just proper to be aware of their actual and operating voltage rating to prevent any unwanted faults during operation. Because of this, Zener diodes have to be tested physically by not just looking at what is written on its casing. In this circuit, the half wave rectification system is composed of 1N4002 diode D1, 470 uF capacitor C1, and 230 VAC/12 VAC transformer T1.

The use of push button switch S2 is to pass DC current from the current limiter Q1 and the Zener diode DZ that is being tested. The current is being stabilized by Q1 to the value of 10 mA without reference to the Zener voltage that is attached to connector J1. The other connector J2 will be connected to the voltmeter which will show the voltage on the digital voltmeter. The circuit can be measured to a maximum of 25 Volts. For Zener diodes, a low voltage measurement will be likely 0.8 V which would signify the breakdown voltage. If the diode is connected in reverse, changing the polarity can be done. No reading will show in the case of reversed probe. An indication of having leakage or shorted Zener diode is when two readings are showing in the result.
READ MORE - junction field effect transistor (JFET)

Selasa, 05 Juli 2011

LED drivers


Intersil's new LED drivers provide the best accuracy of the current industry and channels are suitable for small-medium LCD backlight on smartphones, tablets and sub​​-notebooks.

The ISL97682, ISL97683 and ISL97684 is a compact 2 -, 3 -, 4-channel LED drivers that operate at input voltage range of 4V to 26.5V, and provide outputs up to 45V. The device can also operate from inputs as low as 3V and provide output to 26.5V in the bootstrap configuration, making them suitable for systems using a single lithium-ion batteries.

The device incorporates an optional automatic switching between PWM and PFM mode, to provide the best (up to 90 percent) power efficiency in input voltage and output load range. All devices feature current 1.5 percent accuracy and channel-to-channel matching is currently 0.7 percent, to provide uniform backlighting for the 6-inch to 15 inch TFT LCD panel. High performance and versatility of this product family also makes it suitable for industrial and automotive displays.
Features and Specifications

The minimum supply voltage of 3V (using a bootstrap operation) means no 5V bias supply is required to achieve very high efficiency

Optional channel-to-channel phase shift control to reduce video noise and audio interference

Channel-to-channel current matching of 0.7% ensures the uniform brightness of the backlight

Adjustable noise up to 30kHz dimming frequency ripple on top of the range shift in audio, eliminating the

Open-string, shorted-strings, over-voltage and over-temperature protection devices and systems save in case of failure
READ MORE - LED drivers

MLCC


Choosing the best chip multilayer capacitors (MLCC) for an application can involve a difficult trade-offs involving stability, capacitance and cost. European passive component manufacturer, Syfer Technology has introduced various devices that increase choice and reduce the compromise.

For applications that require maximum stability, the capacitor dielectric chip based C0G/NP0 is an obvious choice as the capacitance is not different from the applied voltage. But what if you want to capacitance values ​​higher than the maximum of a few nF usually available in C0G?

X7R capacitors deliver higher capacitance, because they have a dielectric constant in the region 2000-4000. With more capacitance per unit volume, they are generally smaller for comparable values ​​of capacitance, and usually costs much lower than the C0G. However, the variation of capacitance with temperature can be as much as ± 15% over the temperature range from -55 ° C to 125 ° C with no voltage applied. In fact there are no limits at all are determined to X7R with a voltage is applied, and so significant capacitance loss can occur. This effect is magnified for the dielectric is less stable.

But now X7R dielectric MLCCs are available from Syfer with capacitance variation is defined under the DC voltage is applied, at full operating temperature range. Derating or using high-voltage rating may reduce the capacitance drop, but where an application requires a more stable performance with minimal voltage derating the part is perfect. The advantage of the device with clearly defined limits to the fluctuations is that they give designers the data they need to make informed choices for their application.

Syfer range of TCC / VCC X7R MLCCs are available in two versions. "B" dielectric in accordance with MIL STD code BX dielectric and the IECQ-CECC standard 2x1, while the "R" code dielectric (in accordance with MIL STD BZ dielectric and IECQ-CECC standard 2C1.) The 2x1 (BX) devices, for example, is the most stable voltage version of the X7R, at +15 to -25% load capacitance with the full rated DC voltage applied at full temperature range. The 2C1 (BZ) offers to fill 20% -30 capacitance.

The 2x1 (BX) range includes devices rated at 50V, 100V and 200V, and with a capacitance range from 100pF to 4.7nF (50V, 0603), through a 2.7nF to 180nF (50V, 1808) up to 15nF to 1μF (50V, 2225 ). Comparable devices in the range (BZ) 2C1 is 100pF to 5.6nF (50V, 0603), 2.7nF to 220nF (50V 1808), and 15nF to 1.5μF (50V, 2225).

This X7R MLCC dielectrics range is suitable for use in a variety of coupling and power supply through the application, while the high voltage types are particularly sought after in switching power supplies, dc-dc converters, automotive and aerospace equipment.

The devices are available with FlexiCap ™ terminations Syfer cessation using the flexible material it owned, which makes them much more resistant to damage by bending or flexing, and when under pressure and extreme temperature cycling. Termination alternatives are also available.

Surface mount capacitors already in production and available immediately at 8 weeks of lead time from Syfer of Norwich, England manufacturing facility. The device is fully RoHS compliant.
READ MORE - MLCC

GPS




The GPS system is run by the U.S. Department of Defense. It consists of 24 operational satellites although there are some extras in orbit as spares in case of catastrophic failure even if each satellite is built to last for ten years. Navstar satellites are named satellites and each weighed approximately 1860 pounds. They are about 17 feet across with the solar panels extended, and they send about 50 watts, although the solar panels generate about 700 watts.

Satellites are one of six orbits. It is in a plane tilted about 55 degrees to the plane of the equator and there are four satellites in each orbit. Orbit about 20,200 km above Earth's surface and satellites travel at a speed of about 14,000 km / hour (ie about 8500 mph) which means they complete each orbit around 12 hours.

Global Positioning System (GPS) is a space-based global navigation satellite system (GNSS) that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver.

The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are travelling at speeds of roughly 7,000 miles an hour.

GPS satellites are powered by solar energy. They have backup batteries onboard to keep them running in the event of a solar eclipse, when there's no solar power. Small rocket boosters on each satellite keep them flying in the correct path.

Here are some other interesting facts about the GPS satellites (also called NAVSTAR, the official U.S. Department of Defense name for GPS):
The first GPS satellite was launched in 1978.
A full constellation of 24 satellites was achieved in 1994.
Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
Transmitter power is only 50 watts or less.

GPS satellites transmit two low power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.

A GPS signal contains three different bits of information - a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information. You can view this number on your Garmin GPS unit's satellite page, as it identifies which satellites it's receiving.

Ephemeris data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.

The almanac data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system.

Sources of GPS signal errors

Factors that can degrade the GPS signal and thus affect accuracy include the following:
Ionosphere and troposphere delays - The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error.
Signal multipath - This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors.
Receiver clock errors - A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors.
Orbital errors - Also known as ephemeris errors, these are inaccuracies of the satellite's reported location.
Number of satellites visible - The more satellites a GPS receiver can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground.
Satellite geometry/shading - This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping.
Intentional degradation of the satellite signal - Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.
READ MORE - GPS

Senin, 04 Juli 2011

Antenna diplexer


Antenna diplexer
A brief overview, a tutorial on the basics of antenna or RF diplexer diplexer used for purposes including enabling a single RF antenna for use by several transmitters .

An antenna or RF diplexer diplexer is a unit in a single application can be used to allow more than one transmitter to operate on a single RF antenna. Sometimes these units can be called antenna duplexers. Typically an antenna diplexer will allow the transmitter to a different frequency operation using the same antenna. In other applications, an antenna diplexer can be used to allow a single antenna to be used for transmission on one frequency band and receiving on other bands.

Antenna diplexers find many uses. In one common example of an antenna or RF diplexer diplexer used in cellular base station to allow it to send and receive simultaneously. The diplexer antenna allows the system to use the same antenna while preventing the transmitted signal from reaching the receiver and the input block. In other applications diplexer may be used by broadcast stations transmitting at different frequencies at the same time using the same antenna. Use of diplexer allows a single antenna to be used, while preventing the output of a transmitter which fed back into the other output.

Diplexers small antennas can be used in a domestic environment to enable multiple signals to run along a single feeder. In one application may allow a single feeder to be used for television and VHF FM radio reception, or to allow television signals from terrestrial and satellite voice box low (LNB) to pass on the same lead. This RF diplexers are usually relatively low cost as not nearly as demanding specifications that are used for professional installation of the RF diplexer.

Basic concept of antenna diplexer

There are a number of ways to implement the RF diplexers. They all involve the use of filters. In this way the path to a different transmitter and receiver can be separated according to the frequency they use. The easiest way to implement the diplexer is to use low pass and high pass filter despite the band-pass filter can be used. In this way diplexer routes all signals at frequencies below the cut-off frequency of low pass filter to one port, and all signals above the cut-off frequency high pass filter to another port. Also here are the street from between two long-distance from the filter. All the signals that can pass through low pass filter in the diplexer will not be able to pass through a high pass filter and vice versa.


A further feature of the RF diplexer instead of allowing the impedance seen by the receiver or transmitter to remain constant, although the load is connected to another port. If the filter is not present and the three cable ports in parallel, both the antenna and the two transmitter / receiver will see the correct impedance port.

Filter RF diplexer requirements

When designing an antenna diplexer number of parameters should be considered. One is the level of isolation required between the port for high and low frequency transmitter / receiver. If the diplexer must be used purely to receive, then the need for high levels of insulation is not so high. Even the filter provides a relatively simple isolation sufficient to ensure that each recipient sees the proper impedance and input signals are routed to the right without losing sight. Even the level of 10 dB of isolation would be sufficient for many installations. For diplexers are used to divide and combine TV and VHF FM radio with a single line, te level of isolation may be very low.

The next case is when the diplexer that will be used for transmission only. It will be necessary to ensure that the level of power transferred back to the second transmitter is small. Power is fed to the output of the transmitter in this way can cause intermodulation products that may radiate and cause interference. It is also important to ensure that the transmitter to see the true impedance, and that the presence of a second transmitter does not affect the impedance seen by the first. Usually the level of isolation between the transmitter port 60-90 dB may be required.

The last case is where one of the ports used for transmission, and the other for receiving simultaneously. In this case a very high level of insulation needed to ensure that a minimum level of transmitter power reaches the receiver. If high levels of the signal transmitter reaches the receiver, it will be desensitised prevent proper reception of the signal needed. Levels over 100 dB isolation is usually required for this application.

Band pass filter

In some cases the band pass filter can be used. It can be used where a relatively narrow bandwidth required for one or both of the transmitter / receiver port. Sometimes a resonant circuit which is very high T can be used. Using this approach a high degree of rejection can be achieved. Often repeater stations that receive and transmit on one channel on another simultaneously using diplexers which utilizes this approach.

Summary

Although the antenna diplexers mainly used in specialized applications, which enables a single RF antenna for use by more than one transmitter or receiver, they remain an essential element of many installations. For example, cellular technology will be much different if they can not be used and the RF antennas for cellular base stations will be much more complicated. Similarly, antenna diplexers are used in many broadcast applications allow a single large RF antenna for use by more than one transmitter.
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RF Antenna


RF Antenna or antenna does not radiate the same in all directions. It is found that any realization of RF antenna design will radiate more in some directions than others. The actual pattern depends on the type of antenna design, size, environment and other factors. The pattern directions can be used to ensure that the power of radiation is focused on the desired direction.

It is normal to refer to the pattern in terms of direction and get the transmitted signal. It is often easier to visualize the RF antenna that radiates the power, but the antenna is doing exactly the same way for acceptance, have identical numbers and specifications.

In order to visualize the ways in which the antenna radiates a diagram known as a polar diagram is used. This is usually two-dimensional plot shows the intensity of radiation around the antenna at any point to a particular field. Usually the scale used is logarithmic so a difference can be easily seen in the plot. Although the antenna radiation pattern varies in three dimensions, it is normal to make the plot in a particular plane, usually either horizontal or vertical because these are the two most frequently used, and simplifies the measurement and presentation. An example for a simple dipole antenna is shown below.


Antenna design is often categorized by their type of polar diagram shows. As an example of omni-directional antenna design is one that radiates equally (or approximately equal) in all directions in the field of interest. Design an antenna that radiates equally in all directions in all planes is called an isotropic antenna. As already mentioned it is not possible to produce this one in reality, but useful as a theoretical reference for multiple measurements. Other RF antenna shows a highly directional pattern and can be used in a number of applications. Yagi antenna is an example of directive antenna and probably the most widely used for television reception.


RF antenna beamwidth

There are a number of key features that can be seen from the polar diagram. The first is that there is a main beam or lobe and a small lobe. It is often useful to determine the RF antenna beam-width. It is considered as the angle between two points where the power falls to half its maximum level, and as a result are sometimes called half-power beam-width.

Antenna gain

An RF antenna emits a given amount of power. This is the power dissipated in the resistance of the antenna RF radiation. Isotropic radiator will distribute is the same in all directions. For an antenna with a directional pattern, less power will be radiated in several directions and more in others. The fact that more power is radiated in the directions given implies that it can be considered to have an advantage.

Gain can be defined as the ratio of the signal transmitted in the direction of "maximum" with a standard or reference antenna. This can sometimes be called "profit in the future". Figures obtained and is usually expressed in decibels (dB). In theory the standard antenna can be almost anything but two types are generally used. The most common type is a simple dipole as it is easily available and are the basis of many types of antennas. In this case the gain is often expressed as the advantage of being expressed in decibels dBd over a dipole. However, the dipole radiates not the same in all directions in all planes and isotropic sources are sometimes used. In this case the gain can be specified in dBi gain in decibels is more than an isotropic source. The main drawback to using isotropic source (dBi antenna) as a reference is that it is impossible to realize in practice and that the figures using only a theory. However it is possible to connect two advantages as a dipole has a gain of 2.1 dB over an isotropic source is 2.1 dBi. In other words, the figure is expressed as an advantage over an isotropic source will be higher than 2.1 dB relative to dipole. When choosing an antenna and see profits specifications, be sure to check if the gain relative to a dipole or isotropic source, namely the figure of the figure dBd dBi antenna antennas.

Apart from the advantage ahead of an antenna is another important parameter is the ratio of front to back. It is expressed in decibels and as the name suggests it is the ratio of the maximum signal in the forward direction for the signal in the opposite direction. This figure is usually expressed in decibels. It is found that the antenna design can be customized to provide maximum benefit both advanced from front to back ratio is optimal as the two usually do not coincide exactly. For VHF and UHF operation most designs are usually optimized for optimum benefit to the front as this gives a maximum signal radiation in the required direction.

RF antenna gain / beamwidth balance

It may seem that maximize the gain of the antenna will optimize the performance of the system. This may not always be the case. By the very nature of gains and beamwidth, increasing the gain will result in reduction of the beamwidth. This will make setting the direction of the antenna is more critical. This may be quite acceptable in many applications, but not in others. This balance should be considered when designing and setting up radio links.
READ MORE - RF Antenna

Antenna Resonance


Antenna Resonance

RF antenna comprises a tuned circuit inductance and capacitance, and as a result he has a resonant frequency. This is the frequency where the capacitive and inductive reactances cancel each other. At this point the RF antenna appears purely resistive, the resistance to be a combination of loss resistance and radiation resistance.


It is important to match the polarization of the RF antenna to that of the incoming signal. In this way the maximum signal obtained. If the polarization of the RF antenna is not matched with the signal corresponding decrease in signal level. This was reduced by a factor of cosine angle between the polarization of the RF antenna and signal.

By the polarization of the antennas located in free space is very important, and obviously they must be in exactly the same plane to provide optimum signal. If they are at right angles to one another (ie cross-polarized) then in theory there is no signal will be received.

For terrestrial radio communication applications has been found that once the signal has been transmitted then the polarization will remain the same area. However, reflections from objects on the road can change polarization. As the received signal is the sum of the direct signal plus a signal reflecting the overall polarization signal can be changed a bit though still broadly the same.

Polarization category

Vertical and horizontal are the simplest form of antenna polarization and they both fall into the category known as linear polarization. But it is also possible to use circular polarization. It has a number of benefits for areas such as satellite applications where it helps overcome the effects of anomalous propagation, ground reflection and spin effects that occur in many satellites. Circular polarization bit more difficult to visualize from a linear polarization. However it can be imagined by visualizing the spread signal from the RF antenna that rotates. End of the vector electric field it will be seen to trace a helical or corkscrew as it travels away from the antenna. Circular polarization can be viewed either right hand or left depending on the direction of rotation as seen from the transmitter.

Another form of polarization is known as the polarization ellipse. This occurs when there is a mixture of linear and circular polarization. This can be visualized as before by the end of the electric field vector tracing out an elliptical-shaped bottle opener.

However it is possible for linear polarization antenna for receiving circularly polarized signals and vice versa. The power will be the same whether the antenna is linearly polarized mounted vertically, horizontally or in another plane, but directed the signal arrives. There will be some degradation because the signal level will be 3 dB lower than if a circularly polarized antenna of the same meaning is used. The same situation occurs when a circularly polarized antenna receiving the signal is linearly polarized.

Application of antenna polarization

Various types of polarization are used in different applications to allow their profits to be used. Linear polarization is the most widely used for radio communications applications most. Vertical polarization is often used for mobile radio communications. This is because many antenna designs have a vertical polarization omni-directional radiation pattern and that means that the antenna should not be re-oriented as a position like that always happen to the mobile radio communication as the vehicle moves. For the other radio communication applications the polarization is often determined by considerations of RF antennas. Several multi-element antenna array can be mounted in a large horizontal field more easily than in the vertical plane. This is because the RF antenna elements at right angles to the vertical mast towers they are mounted and therefore by using an antenna with horizontal elements there is little physical and electrical interference between the two. This determines the polarization of the standard in many cases.

In some applications there is a difference between horizontal and vertical polarization performance. Eg medium wave broadcast stations generally use vertical polarization because the ground wave propagation over the earth is a far better use of vertical polarization, while the horizontal polarization shows marginal improvement for long-distance communication using the ionosphere. Circular polarization is sometimes used for communication satellite radio because there are some advantages in terms of propagation and in overcoming the fading caused if a satellite changes orientation.
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