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Electronics => Projects, Designs, and Technical Stuff => Topic started by: Emi on November 23, 2016, 10:02:54 am

Title: Good SDR dongle as simply SA & SG
Post by: Emi on November 23, 2016, 10:02:54 am

Hi, another foolish question  ;D
Are usb SDR dongles like AirSpy, RSP1/2, and similar suitable for an "almost decent" hobbystic Lab SA?
Could Lime SDR and Hack RF  be used as basic wide band signal generator  too ?

Forgive my strange questions but i'm quite tweaking oriented guy :)

Title: Re: Good SDR dongle as simply SA & SG
Post by: Scrts on November 23, 2016, 04:33:07 pm

Well Red Pitaya was created for this purpose. I believe hackrf or any other SDR could be used if that is sufficient for your needs.

Title: Re: Good SDR dongle as simply SA & SG
Post by: PointyOintment on November 24, 2016, 10:27:36 am

SmartScope too.

Title: Re: Good SDR dongle as simply SA & SG
Post by: phil on November 24, 2016, 11:18:29 am

A HackRF can be a powerful tool if you know your way around GNU Radio Companion.
However, as with other SDRs, you have to know its limitations and work around them.

For example, the output power level (when used as SG) is not flat over frequency and not calibrated. You have to tweak it by manually setting IF and RF gain in your GRC flow graph. That means you need a power meter or some other device to actually measure output power at the frequency you are interested in. Using another SDR has the same problem: You need to calibrate it first.

You *can* use a HackRF for simple RF-work, but you need a way to measure its performance first. Meaning, you need access to a decent SA/power meter and SG at least once.
My particular HackRF needs 8dB IF gain and 16dB BB gain to get "accurate" power level readings. Beware: Its easy to saturate the IF/BB amps, you need some input attenuators.

If you plan on doing serious RF work, don't buy a HackRF. Go for something like the VNWA 3.
I do, however, use my HackRF quite often for filter analysis where absolute output power matters little.

Title: Re: Good SDR dongle as simply SA & SG
Post by: Emi on November 24, 2016, 01:43:59 pm

Thanks guys, Phil, you've been really clear .. :-+
I was a little optimistic in fact...And i'm not a GNU guru too..

Title: Re: Good SDR dongle as simply SA & SG
Post by: tggzzz on November 24, 2016, 04:40:43 pm

With a little imagination and understanding, the $15 SDR dongles can - within their limitations - be surprisingly useful.

I've noted how I've used one to make a 1.5GHz spectrum analyser, 1.5GHz scalar network analyser, measure 650ps risetimes, and a TDR that can resolve discontinuities 4cm apart.

FFI including the utilities I created, see https://entertaininghacks.wordpress.com/category/frequency-domain-analysers/