Tuesday, January 29, 2019

RTL-SDR for spectrum analysis

Since getting back in to RTL-SDR for my recent foray into decoding DMR, I found that these are a very useful (and low cost) bit of gear.

At the last ham radio meeting at Dural, I bought a Shure radio microphone and when I got home I wanted to find out what frequency it was on. Cranking the knob on a receiver was taking forever so I decided to look into scanning broadly with RTL-SDR.

There is a bundled tool called rtl_power which seems perfect for this but it creates a CSV file that's a bit annoying to look at or graph. Now I've stumbled upon RTLSDR-scanner.


RTLSDR-scanner is a python module which you run from the command line. You give it a low and high frequency and it quickly scans and displays a nice graph which can also be exported and looks like this:

(Click images to enlarge by the way). RTL-SDRs don't have much dynamic range so I don't really think this would be good for real spectrum analysis tasks, like finding spurious emissions from transmitters, but for finding the output of a mystery radio mic (622MHz by the way) it was perfect.

Alternatives

There is some great software around for driving RTL-SDR and other SDRs. One that looks terrific is Spektrum but I can't get it working on my Ubuntu or Windows machines here.

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