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Wideband RFI Sniffer Very Useful

wideband rfi sniffer

You can use your TinySA spectrum Analyzer as a close-in wideband RFI sniffer to check performance of how badly consumer electronics gear interferes with radio listening.

For a few years, I have been running a matched pair of 20 inch LG monitors on my radio computer, with a GeoForce dual DVI video card. I purchased all of these used on Kijiji. I found that using these monitors with DVI produced the least amount of RFI. Dual monitors is pretty much essential for running multiple SDR, not to mention electronics applications like logging software, digital decoding, and KiCAD.

All good things come to an end. One of my LG monitors died recently. So, I went hunting around the house for a replacement and chose the Samsung 22″ from my workshop. And bang, tons of RFI was back.

So, I used my cheap TinySA spectrum analyzer as a wideband RFI sniffer to check out all of the monitors in my house. I set the scan range to 50 MHz with the view of finding the best and worst performers for radio frequency interference in the shortwave bands.

Above, you can see the RFI emissions from this monitor. The yellow line is “monitor on”; the red line at the bottom is “monitor off”. You will see above a 20+ dB increase in noise across HF from the Samsung when turned on. My spectrum analyzer showed worst performance in the 17-22 MHz range, which matched to what I was hearing on the radios.

RFI emissions are strongest in front of the monitor, where there is really no shielding. Emissions were about 10 dB less of the back and sides. My built in whip antenna does not work well on HF, but is good enough to pick up radiated signals at short range.

Wideband RFI Sniffer checks things out

I tested five monitors this way to find the unit with the least RFI, and swapped this in as my second radio PC monitor. Along the way, I also moved the entire radio PC setup to the lab – monitors, mouse, keyboard, speakers, USB cables, etc.

By running my TinySA along all the equipment and cables, I was able to satisfy myself of low RFI radiated emissions from the complete system.

As a side note, I noticed that most monitors gave off a lot of RFI in the VHF range, which is not a big deal for me, but could be for you. You can buy a TinySA online for around US$ 50.


  1. Guy Atkins says:

    Hi John,

    I bought a 20 inch LG “ultrawide” monitor a couple of years ago for the same reasons to use as a 2nd screen. A DXer friend of mine bought the same model, as it was a good value. I’ve noticed that mine too is very low on the RFI scale, so perhaps we have the same one.

    I’m finding it’s important to have very high quality coax for the entire run to the receiver…not just the main coax lead-in but jumper cables too that might be placed after antenna splitters, bandpass/highpass filters, RFI choke boxes, etc. I like to use “Airborne 5” or “Hyperflex 5” coax from Messi & Paoli out of Italy. This is pricey, but extremely high quality cable: https://messi.it/en/home.htm

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