Using TV Tuner as front-end for Communication Receiver

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abasir

Joined: 16 Mar 2002
Posts: 39
Helped: 1
Location: Malaysia

30 Nov 2004 8:55 Using TV Tuner as front-end for Communication Receiver

I came across the following site (http://hem.passagen.se/communication/supertuner.html) using TV tuner as communication receivers. The tuner mentioned is difficult to source now. With the availability of cheap TV cards for the PCs (with built in tv tuner outputting video and audio directly), can the following be done (the tuner will be removed from the PCB and controlled directly with microcontroller/PC using I2C) :

TV Tuner Video Output --> Mixer (with DDS LO) --> 455kHz filter --> Demodulator (FM, AM, CCW, etc) --> Audio.

The main reason for the h(at)ck is to allow 1Hz resolution to frequency change. Most tuners only allow 50kHz resolution.

Thanks & regards,

IanP

Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast

30 Nov 2004 9:25 Re: Using TV Tuner as front-end for Communication Receiver

I don't think you can do it this way.
The output from TV tuners from computer cards is the baseband video signal (after AM-demodulation) and will be usless for you.

cozturk

Joined: 02 Apr 2002
Posts: 110

30 Nov 2004 11:06 Using TV Tuner as front-end for Communication Receiver

Fine tunning can be useful for Audio IF stage. So we can step in 50kHz step. For FM radio mode, tuner's step can be made 31kHz. and it can be reduced for changing 4MHZ xtall to 3.58MHZ also.

Of course we can take IF signal from mixer IC to AM demodulating and for our narrow band IF stage. Perhaps A cheap AM/FM radio can be used. I tried it for FM demodulating. Successful. But AM not tested. Radios LO should be tunned for 30 MHZ .

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abasir

Joined: 16 Mar 2002
Posts: 39
Helped: 1
Location: Malaysia

30 Nov 2004 15:42 Re: Using TV Tuner as front-end for Communication Receiver

IanP wrote:

I don't think you can do it this way.
The output from TV tuners from computer cards is the baseband video signal (after AM-demodulation) and will be usless for you.

Thanks for highlighting the above to me. I'll pry open the tuner module and take the VIF output for the task. Any good site describing TV tuner operations? I've always been 'digital' so this RF stuff is not my domain Smile

abasir

Joined: 16 Mar 2002
Posts: 39
Helped: 1
Location: Malaysia

12 Dec 2004 7:07 Using TV Tuner as front-end for Communication Receiver

Gurus,

Could I use the intercarrier signal instead of the VIF? The tuner I have uses TDA9801 that output video/audio intercarrier. I plan to use the intercarrier, mix it with DDS signal and feed the output to the 5.5MHz filter and FM demod unit of the TDA9801. Don't want to redo the circuit already there Smile

Thanks