Last week about tuesday, I started experiencing an interference on the input of our MacDonald Pass UHF repeater. The signal interfering was a rythmic pulsing signal that seemed very broadband and sounded almost like video buzz. As we have had problems with a Television station that goes spurious whenever there is ice on their antenna, I wrote it off as these guys. They are on a Mountain about 15 to 20 airmiles away.
Next day, the signal was still there, and it was drifting up and down from our input. It proved to be very broad in that when the signal was found 50Khz away, the ticking pulse was still heard on our repeater input on weaker signals. After another day goes by, the signal is still present. So while in town (Helena, MT, pretty small) last Thursday for a couple hours, I loaded up my Receiver and grabbed a portable and decided to try and hunt this down. I was getting more convinced that it was not the TV station.
A couple of area hams had gotten some good directions of the signal with their yagi's so I started driving around looking for it. To make a long story short, after a couple of hours (no yagi for me), I finally found what seemed to be the source of the signal as I was getting full scale signals on an Icom R8500. It was at a RV sales lot and office. This was at night and they were closed, but as I pulled up next to their gate to the back yard, the signal was very strong. I also dialed up and down the band and found several other strong pulsing signals and a couple of steady signals, some in the ham band, some in the commercial band.
Came back the next day and talked to the folks. I believed the signal may have been coming from the shop in the rear or possibly from one of the RVs TV amplifiers, although I doubted they were powered up. We walked to the shop with my portable and no antenna and the signal got stronger and stronger. Now here is the very odd part.
It turns out that the signal(s) were coming from a pair of Motorola Family Radio Service Talk-a-bouts that were sitting in a dual pocket charging stand. Both radios were turned OFF and had not been used in months. Removing the radios from the charger stopped the signal. Putting them back started it up again and moved the freq some. Didn't spend time feeling if one radio was warm or not, or which radio may have been it, or if the charger itself was doing this. They simply unplugged it and said the radios were junk and didn't need them anyway. I beleive I had heard a similar story before, but for those out there looking for interference, watch out for those powered off UHF FRS radios in chargers
)in Florida and I get hit with all sorts of crap, one of which is the radiating TV amps in RVs. There are probably 20 RV parks within 10 miles of the site, as soon as I start DFing, they move on. I also had a problem with a new digital TV station on channel 14 on a tower 1 mile away. When they went on the air, it wiped my RX totally OUT on all of my 467-469 freqs and desensed my 457 channels by 25 dB. I was getting -20 dBM noise through the TTA filters AND the window filter at the bottom, even with the amp gain reduced or off. Turns out the TV station had a really bad output signal due to the exclusion of a filter (mask filter I think they called it...) that the transmitter manufacturer omitted for some reason. Since their signal was radiating substantial energy out of their assigned bandwidth, they had to obtain a FCC STA to shut down until it got fixed. This filter needed to be ordered, cost is somewhere around $250K... 
. They are still off the air. Wonder how much desense I'll have when it comes back on and and they're clean?
