Senin, 13 Februari 2012

Parts of the tuner

Parts of the tuner:
A. The selection of channels (selection transmitting stations)
Tuner blocks to choose the wave transmitter to be received, including channel 2 to channel 12 (47-230 MHz) in VHF and each channel has a width of the frequency of 7 MHz. Circuit tuning can be chosen so that resonance the frequency channel of your choice.
In the tuner block are RF amplifier, Mixer and Oscillator. RF amplifier to choose the transmitter to be received, and then supplied to the mixer, oscillator generating a frequency of certain magnitude to the comparison frequency to be received RF amplifier is then supplied to the mixer and the filter eventually produce a new frequency is out of the 38.9 MHz is the carrier frequency images therein there is a synchronization signal and 33.4 MHz is the frequency of sound carrier and the second frequency is forwarded to the video amplifier IF.

2. Amplifier of high frequency (HF Amplifier)
Prior to the series mixing (mixing) wave tv amplified by the amplifier HF. Because the ratio S / N (the comparison signal / noise) at the receiver a color TV set by amplifier HF, then strengthening HF should be able to produce amplifier (gain) is great. Also requires a distortion of small even when a wave of TV a large input. Then the required voltage AGC (Automatic Gain Control / control amplifier automatically) to the amplifier HF was mounted a series of neutralization, the amplifier HF ​​to prevent parasitic oscillation occurs. Characteristic frequency response of the amplifier HF in the field of frequency channel receiver, must be equal as possible and the difference reinforcement between the canals received should be as small as possible.

3. Mixer (Mixer)
Wave TV received TV mixed with the output local oscillator using a mixer (mixer) and converted into a signal IF (Intermediate) images that have a frequency equal to the difference in both frequency earlier. The carrier frequency signal IF the image is 38.9 MHz and the carrier frequency of the sound signal is 33.4 MHz.

Canal No. 3:
Frequency Osc
38.9 MHz
33.4 MHz

55.25 60.75 95.15 MHz

4. Local oscillator
Frequency mixer (Frequency local) generated by local oscillator, and supplied to the mixer (Mixer). Frequency can be changed depending on the channel selected recipients.
As the local oscillator is usually used oscillator Colpitts because of the nature of its stability and simple structure his series. There are two ways to choose the frequency of the first local by changing the coil resonance and the second by controlling the bias voltage of the diode capacitance is variable.

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