Sabtu, 26 Maret 2011

Modulation Mode Operation

Modulation Mode Operation
Amateur radio operators have various modes for the two-way communication. Mode A refers to the way modulated signal during transmission. Frequently used is a form of modulation AM, FM, SSB, and digital. For the signal to be sent and received with easy to read it electronically modulated. Both transmitter and receiver must use the same form of modulation for communication to be successful. Each mode will be discussed below. Table mode which is preferred for voice communication gives some idea of ​​what to expect when you use a certain band. Some modes such as the use Rtty LSB for all bands.

Preferred Mode

The following sound modes used by general agreement:
LSB 160, 80, 40 yards
USB 20, 17, 15, 12, 10 yards
FM 2, 1.25 m and 70 cm. Some USB is also used.

Each mode has its own unique characteristics. One is the amount of bandwidth occupied by the signal. CW is very narrow (less than 250 Hz) while the FM is rather wide (15-20 kHz). A narrow signal means there's room for more signals and thereby further activity on this band. On the other side of the narrow transmit the signal quality is less or information. CW requires the use of Morse code, while the results of high-quality FM signal for voice communication. In each of the following modes are used more briefly discussed.

CW (continuous wave)
Is a simple unmodulated signal unlike others who use some form of modulation. By interfering with the signal with the code, Morse key is sent. So Morse code is not the mode but as the name suggests, the code used to communicate with the control signal CW. Although it takes time and practice to become proficient with the code using the CW is one of the most reliable communication because generally can through the most difficult conditions in which other signals can not.

AM (Amplitude Modulation)
Is the initial mode that is used by hams for voice transmission. AM signal carrier (like CW), the upper and lower sidebands are modulated by varying the amplitude (strength) of the signal. Most of the short-wave broadcast stations use this method. If you tune to the BBC or some of these stations by using either USB or LSB on the receiver, you can hear the carrier as a continuous tone when you move slightly away from the center of the signal. If you listen to around the end of the 80 meter band you might find some ham by using this mode. But the PM to take double the bandwidth of SSB and therefore not widely used in Amateur radio.
SSB (single sideband)
Is a mode where carrier and one sideband of the AM mode has been suppressed. Whether using a USB (upper sideband) or LSB (lower sideband) is more than the signal sideband transmitter is to focus on the use compared to AM. As a result, the signal travels farther and is easier to copy in many adverse conditions. SSB is the telephone mode of choice for amateurs on HF bands.

FM (Frequency Modulation)
Is what you hear on 2 meters when using the phones and work through the repeater club. This is where the most ham mode begins. FM has exceptional quality for voice communication, and generally there is no noise or fading you hear on HF with SSB or CW. However, due to wide bandwidth requirements are usually limited to bands like 2m or 70cm where there is plenty of space. Some FM also can be heard at a distance of 10 meters about 29 MHz.

Digital Mode
Digital modes RTTY but has existed since the very outside of the computer generation. To simplify the use of digital modes-off in (binary 0-1) to send the information. CW is really a basic form of this, although enough. Most digital mode requires a computer that will be connected by radio to assist with sending and receiving data. Most also require a TNC (terminal node controller) with a chip that supports a particular mode. You send the tie on the keyboard and accept the view of information received on the screen. Some of the more popular digital modes are:
# RTTY - Radioteletype (RTTY) using baudot (5 bits per character) or ASCII code (7 bits per character) to communicate. RTTY is almost as reliable as CW and there are many hams who use this mode regularly on HF bands.
# Packet - use the full ASCII character set that allows both the upper and lower case characters in the transmission. The package is free from error achieved by sending data in a small package with little checks. If an error is detected by the receiving station requesting a reply and re-package. It repeated it takes to receive the package properly. When a good signal packets rarely needs to be sent two times but in bad conditions, send back an error packets to slow the exchange of information.
# Tor Mode - TOR means "teleprinting via radio." This mode includes AMTOR, PACTOR, G-TOR and Clover. Basically they all use some variation of the techniques mentioned in the package to ensure error-free transmission. Each uses a special algorithm to generate improved transmission speed and accuracy.
# PSK-31 - is a newcomer to the digital scene and is quickly becoming the primary digital mode. One of the reasons the appeal is that he uses the sound card in the computer to send and receive via radio. No other special equipment is required. PSK-31 uses a very small bandwidth, less than CW and can function well in low signal strength. Unlike the package and the TOR are not free from error.

Fast scan TV (FSTV) and slow scan TV (SSTV)
Mode is used to send pictures or photos via radio. SSTV is generally used on the HF bands and can only send still images because the data rate and low bandwidth. FSTV on the other hand is generally used in the UHF band and can send moving images. Recently, several manufacturers have produced HT handheld radio with built-in camera and screen for use in this mode.

IRLP (Internet Radio Linking Project)
Is a method for connecting the Internet with Amateur Radio. Usually the link is done through a local repeater so you can connect to someone with a handheld. Basically you register with the local repeater and enter the code to connect you to link the Internet. From there you are connected to other repeaters that are also on the Internet. So with your handheld you can take to ham thousands of miles away with the signal quality of local contacts. IRLP is the discovery of Canada by VE7LTD and use Voice over IP (VoIP) to immediately connect one or more repeaters around the world. Now with your basic licensing new radio amateurs were able to use HT to communicate across the world.

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