MY FIRST VHF RECEIVER ...!!!
This is a receiver build using the Analog TV tuner used in old television sets. Its capability and real application limits it to receive analog signals only. I have done some modification to the circuit to make it more selective and flexible. The inspiration that I got to build this circuit comes from the "link" .
As per the test results it can receive almost any analog signals in the range of 85 to 950Mhz which is the bandwidth of the tuner. Using this one can receive commercial FM (WFM), AM (aviation), NFM (used in 2m Ham Band), and also Commercial TV (WFM). As far as I tested it with a 40M antenna I am able to receive all these signals, especially the 2m Ham Band. But I think the reception can be improved with a proper tuned antenna…All the parts and accessories are taken from e-waste bin that gives it a title (DE_JUNK_BEE)...
Talking about the circuit its nothing but a combination of tuner along with a mixer to down convert the IF signal from the tuner to 10.7Mhz IF for generic FM followed by an IF amplifier and FM detector circuit.
As per the European standards for television broadcast PAL system is used and India is using the same for the commercial TV broadcast. So the IF adopted is favorably 38.9MHz which will be the output of the tuner. The mixer designed is using the LA1185 with local oscillator frequency of 28.244MHz which makes me get an output of ~ 10.7MHz from mixer. Can be modified with mixers like SA602 and FM detectors like MC3362.
This IF is the passed to an IF amplifier cum Detector build around TBA120S chip. Which lets me give an audio frequency output which is further amplified using the LM386 general purpose audio amplifier circuit. I have not included the audio amplifier circuit as it can be found in internet.
The tuner and all other components except audio amplifier is taken from old television set. I have not used any SAW filter as it is attenuating the IF from the tuner and it works well for my receiver. I had tried with a 38.9MHz saw filter at the mixer front end but it the response was poor so i bypassed it.
|Top view showing Antenna Port and Power supply port|