Affordable RF scanners

Ben Lawrence

Mar 2, 2011
I have a venue running 20/25 Sennheiser wireless beltpacks (paddles and combiners) that have been running into some interference. I run the built in scan to assign open channels but still seem to be running into some issues.
Is there a usb dongle or something where I could get an image of whats happening in the radio spectrum? I think I looked a while back and the hardware out there was pretty pricey. Now I have seen some phone apps and such that display strength of nearby 2.4g-5ghz signals and wondering if there might be an equivalent available for a pc except of course the 400-600mhz range. Would be awesome to see a visual display of whats going on.
The snag you have is that you can now see what is in the spectrum, you have to learn to interpret what you see, and the first thing is you have already broken one of the rules. Interference. So many different types and they sound different, so the first step is identifying the kind of much interference

The first step is always to work out what is going on. Step one is when you hear something, you switch off all your transmitters, bar the one pair hearing the ‘interference’. Very often, the interference goes away. The problem is your own system. This sort of interference wont be easy to spot with any kind of analyser. Intermodulation interference is in my experience the most common. Nasty warbling noises or random dropouts that happen when two or more active transmitters combine to annoy the receivers. So many times it is where users have chosen frequencies at random, seeing a gap, and plonking a new transmitter in it. Then when the people using the transmitters suddenly move to a location all hell breaks loose.

an analyser is great for showing you a spike for each transmitter, and if there should be seven, and you count eight, then you can see the problem. The trouble is most times you will NOT hsve Co-channel interference, as in somebody else on the same frequency as that’s actually quite uncommon unless you are on broadway or in the west end. Most interference problems are simply using the wrong frequencies. Which is why all the manufacturers have sets you can use that don’t annoy each other. Co-channel and intermod sound very different. It is possible it’s Co-channel of course and the news folk get this as their common one, where they have one transmitter and one receiver on the news crew camera, but there are lots of news crews. Analysers are great for them as it clearly shows what is being used. Multiple mic systems are usually planned. to use a recent one of mine. I was managing a very big theatre show. The audio gear came from one company, with crew. Their frequency planning was done in advance and despite lots of channels running, was interference free. However, it took a long time to find just a few extra channels when somebody wanted another radio system in the same venue for a few nights. We simply insisted our system would be the only user of our band, and the other folk changed their two systems for ones in a different band and that was fine. Our A2 spotted the problem as soon as they powered up. He had marked the analyser screen with our 15 peaks and the two new ones had been picked via sennheisers tuning system into gaps in ours. These two new ones caused problems for us, but the analyser showed why. A run up four flights of stairs killed the problem before it even started. Their Tec person was clueless, so didn’t even understand what he’d done, thinking empty channel, Sennheiser says good, use it!
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