Re: [Discuss-gnuradio] AM receiver

[Martin Dvh]

Gituma Nturibi wrote:

> First I thank Eric and Michael for their input about my previous query- 
> It was helpful but designing a superhet radio receiver is not as easy as 
> it sounds.
>
> I'm back again with a few questions about GNU radio. As I had said 
> earlier I was thinking about creating an Fm receiver. However cost and 
> complexity considerations have made me think about trying AM reception 
> instead. Taking into account I'm based in Kenya so shipping would be an 
> issue and a budget of about $120, very small!
> The problem is that I'm on a tight time schedule and require to get the 
> project up and running soon. So I would like to know what is the best I 
> can achieve using a PC sound card or some other cheap ADC board.
>
> I would also like to know where I can find the code for AM reception 
> particularly the MW band.
>
> I'm also looking for information on FM tuner cards- Is there a way to 
> tap the IF from the card and use it as a front end?
I have done this using a bt878-chip based  TV-tuner card.
(Which can also tune the 88-108 Mhz FM band, although it was NOT a FM/TV tuner 
card)
The problem is that most analog tv-tuner-cards use a tuner block which does not 
export its IF signal to the outside.
So I had to open up the tuner-block, figure out where the IF signal was, solder coax cables (balanced signal) to the tiny traces and connect these cables to a 
fast ADC using a balanced to signle ended transformer.

I tried to use the video-capture input of the tuner-card itsself as a fast adc.
I had to write a new (linux) driver for the capture chip (Bt878)
Only to find out I could receive some signals with it (FM) but I was missing 
samples and the signal level was much too low.

At the moment I am investigating modifying a TV-capture cards with different 
capture chips and tuners.
The pcHDTV3000 card looks to be promising but writing the driver and the 
modification of the hardware is not finished yet.

So, yes using a TV-capture card (or radio-card) can be a cheap alternative as a gnuradio frontend but only if you have a lot of hardware modification skills, 
linux driver development skills and a lot of time.
Or if you are not in a hurry and wait untill others (like me) have figured this 
out for you.

If you are in a hurry I would suggest the SSRP as a cheap ADC frontend.
I think you can do AM (MW) with it with only a wire as frontend.

Greetings,
Martin


> I would appreciate 
> input on this and where I can get more info on the internal workings of 
> an FM cards tried to search for some on the net and got basically nothing.
> Still trying to find out the specifications and the capabilities of the 
> N1IBT board by willware. Any GNU radio implementation using a Tayloe 
> detector?
> Thanks in advance
>
> Gituma Nturibi
>
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