This is not an endorsement, an advertisement, or an official message from IFI, but I just bought two of these for our robotics club’s use. It’s a frequency checker which scans the 90 channels in the 75MHz range, and is an easy way to look for interference on VEX channels. This is the unit that John V-N recommended for testing, and I found it on sale at Tower Hobbies online for $4.99. That’s “four dollars and ninety-nine cents” in case you thought that was a typo: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJUP3&P=7.
I don’t know why they are selling it so cheaply, but – like I said – I just bought two.
Mine just arrived, and it seems to work well. I tried it with a couple transmitters on different channels and it spotted them both, as you would expect.
I wanted to post a couple details from the instruction sheet to help folks who are thinking about getting it. (These are also mentioned on the Tower Hobbies page that Rick provided a link for, but I wanted to point them out as particularly relevant):
This is because the frequency checker is a scanner - it scans through all the channels every 10s or so. This means that it is watching each channel for about a third of a second every ten seconds. If the interference doesn’t hit at exactly the right time, the scanner won’t see it.
This sounds like it might be relevant if you want to use the frequency checker at a competition.