RF Front end for a ADC

Hello,

I like to do build or buy an RF front end for an ADC to be able to capture RF signal and process with them.

Perfectly I like to cover the frequency range of FM and AM radios (150MHz).

The RF would have an antenna interface and a heterodyne stage. The ADC that I have can sample up to around 100 MSpS but I like that my sampling rate be around 20 to 30 MSpS so the heterodyne should down convert to 10MHz.

For AM radio receiving I think I don't need the heterodyne stage and I can sample at the rate of 1o MSpS.

And my question: Where should I start? Can I buy anything such as this? My budget isn't very high so I can't buy anything more than 100pound or so on.

Any help appreciated.

Best regards

Mansour

Reply to
ma
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A lot of off-the-shelf FM radios use a double-conversion system... an RF stage, oscillator, and mixer, with the output of the first mixer being centered at 10.7 MHz. There's usually a tuned or crystal filter stage of some sort (bandwidth of perhaps 100 kHz) with some amplification, and then a second oscillator and mixer which creates a lower-frequency (often 455 kHz) IF.

You could probably start with an off-the-shelf battery-powered AM/FM radio (a several-decades-old one would probably be easier to work with), tap off the signal at the output of the first mixer, and amplify it enough to give you a useful input for your ADC (a Minicircuits or similar monolithic amplifier would be an easy way to get gain). You might be able to use the existing IF strip and its amplifiers, if you jumper around the crystal or tuned-transformer filters and convert it to a broadband amplifier.

Google for "software radio" - there are a number of projects working on RF front ends and ADCs like this, and there might be some which have a bandwidth as wide as you are looking for.

--
Dave Platt                                    AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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Reply to
Dave Platt

Hello Dave,

Most of them are single conversion. 10.7MHz into a filter (or whatever they nowadays call 'filter'), then into the FM demodulator. The 455kHz section that runs in parallel is for the AM band(s).

The only radios with any decent performance I have seen are the ones over $1000 or the old tube sets.

Regards, Joerg

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Reply to
Joerg

Hello, I aonly need the antena amplifier and hytrodyne section. No demodulation. I want to do demodulation in software. so my questos are:

1- How can I design a simple antenna amplifer that connect to an antena from one side and amplify the signal to a suitable level for a adc (1Vpp). 2- How can I design a hetrodyne section that can convert from 100MHZ to 10MHz?

best regards

Reply to
ma

Hello ma,

You could still use an old radio. Just tap off at the mixer output.

I suggest to get a copy of the ARRL Handbook. That shows in great detail how it's done.

Regards, Joerg

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Reply to
Joerg

"Experimental Methods in RF Design", also available through the ARRL, would also be a good reference source. Lots of detail there about the design of local oscillators, various sorts of mixers, IF amplifiers, and so forth.

--
Dave Platt                                    AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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Reply to
Dave Platt

Hello Dave,

And then there is always the easy way out: Whip out the credit card, buy a Mini Circuits mixer and a nice synthesizer chip from AD. But that kind of spoils the sportsmanship.

Regards, Joerg

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Reply to
Joerg

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