>>1104868Overloading the receiver's front-end, filter/amplifier/mixer circuitry.
It's the reason for the "donut-hole" coverage of higher-power sites. Real close to (or on) the tower, there's too much power into the radio and it'll exhibit that behavior.
It's why when I'm working on VHF systems, I use a UHF or 800meg radio, and on UHF/800 systems I carry my VHF portable.
One site I've worked on in the past was a 350W VHF repeater. Anywhere on that site my VHF portable wouldn't receive anything. UHF worked fine. That site was decom'd a few years ago, 150W 800meg digital put in its place.
In a metal cage like what you've got, you not only have the power from the TX'r, but also reflections bouncing around inside the cage.
Ideally you'd want an anechoic chamber, but those get really expensive (I'm paying about $30/sheet for a 2ft x 2ft x 3/4" thick piece of conductive carbon-loaded RF-absorbing foam for my test/measurement stuff), and a typical anechoic chamber is at least 10ft^3 with a fuckload more foam in there (the pyramidy-style stuff, to deflect the energy into itself and convert that to heat, instead of reflecting it back into the test chamber).
Make sure you've got input/output freqs and tone (needed on TX, on a portable you'll probably want RX tone set too) set right.
If you kerchunk the repeater and hear the carrier delay/channel-free tone, you know you're making it in.
Most repeaters set up properly will have a couple seconds carrier delay, but a channel-free or courtesy beep may or may not be programmed in.
