If you have shopped for test equipment for ham radio use you know that Oscilloscopes and Spectrum Analyzers are not inexpensive. Spectrum Analyzers can be especially hard to justify. So I was interested by the fact that SDRplay includes free software that will turn it’s SDRduo (And some other models) into a software Spectrum Analyzer.
So what do you want a spectrum analyzer for? To look at the output of your transmitter of course!
A quick look at the above picture shows us the old Kenwood is still transmitting a nice clean SSB signal.
Notice there is a bit of a carrier present right on frequency at 14.240?
How to get a sample of your signal
So lets back up a bit and talk about what kind of setup is required to get to this point. The first thing you will need is a way to get a sample of your transmitted signal. You can’t just transmit into the RSPduo at full power. You will immediately destroy it.
I usually use a Celwave 250w dummy load (with a sample port) that I got used from RF Parts for $45. I also have a -50db sample port ( for Pure Signal ) after my linear amplifier that will work FB for sampling your over the air signals.
If none of that helps, there are several other ways to get a sample of your transmissions, from building one into your tuner, buying a test tee, or any number of other ways. The main thing is you are sampling a much lower level signal than you are transmitting.
The screenshot above will look familiar to anyone who has used or seen a spectrum analyzer before.
The sample at the beginning of this article is from a USB transmission on my old Kenwood TS-850S and was made using the built-in screenshot button seen on the menu bar above the black area.
Are you wondering if your radio is transmitting a clean signal?
This is a great use for a spectrum analyzer. See what your transmitted signal looks like!
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Bottom Line
While this setup won’t replace a proper spectrum analyzer or be suitable for applications where a high degree of accuracy is required, it is a nice extra for those who purchased the SDR Play and can live without the high precision.
Give it a try.