Traditional analog fade on one frequency

I have a BCD536HP that I have very little complaints about. My list of systems I listen to is rather small but a certain UHF frequency (423.625) I monitor has an unusual problem I can't explain. I am experiencing this fade effect where either dispatch or a vehicle will be talking and all carrier/audio seems to fade away a couple seconds into the transmission and occasionally comes back. It is intermittent and lately I've noticed sometimes the squelch breaks (I hear nothing) but dispatch comes back to a vehicle.

More frequently I'll hear 'waves' of static as the carrie fades in and back out during a transmission.

If it wasn't happening all the time I'd blame it on some kind of obstruction or wind on the TX antenna, etc.

The antenna for this on my side is a Diamond D130NJ in my attic with 50' of LMR low-loss coax in my attic converted from N to BNC at the rear of the radio. The city transmits off a tower that is, based on google maps, less than 9,000' feet (unobstructed line of sight) away. Due to the elevation of my house my roofline is fairly close to the elevation of the transmitter antenna. (This couldn't be any more perfect of a scenario for a rock solid signal)

What blows my mind is this is the only radio and only frequency this occurs on. I have Yaesu VX-5R handhelds with a rubber duck that I can walk around the house and hear this solid in the basement. I have an old BC780 with a simple mag mount antenna on it feeding a stream just this freq, parked on that frequency, and it doesn't exhibit this behavior at all. If I am driving around in my car my Kenwood DM700 hears this freq without any fade at all.

It finally bugged me enough tonight to post this. I couldn't find any discussion of fading that seemed to be relevant to this experience.

Anyone have any ideas?

Are you sure the carrier is on 423.625 and not heterodyning? That's in the bottom of the 70cm ham band/federal ism-itinerant and above the federal trunked stuff.

Edit: I just read the second part of your question, does the scanner track it better with the antennas from the other radios that are working?

jhal94 said:

Are you sure the carrier is on 423.625 and not heterodyning? That's in the bottom of the 70cm ham band/federal ism-itinerant and above the federal trunked stuff.

Edit: I just read the second part of your question, does the scanner track it better with the antennas from the other radios that are working?

Click to expand...

1. Positive. It's been licensed here for decades. I'm in Northern Ohio so 420-430mhz falls "north of Line A" which Wikipedia recaps really nice (I knew it was Line A but had to go dig...):

By international treaty between the US and Canada, operation in the portion of the band from 420 to 430 MHz is prohibited north of Line A,[5] which runs just south of the Canadian border from Washington state to Maine, and east of Line C, which runs from northeast to southeast Alaska.

Click to expand...

Here is a map in case you've never heard of Line A: OET --Frequency Coordination, Canada

2. Thats a great idea. I am going to try that. I am staring that idea in the face and really needed to be pointed at that

jhal94 said:

Edit: I just read the second part of your question, does the scanner track it better with the antennas from the other radios that are working?

Click to expand...

It may have been that simple. First transmission after swapping the antenna was 100% solid. This may have been a fluke but a statewide VHF simplex PD freq just broke squelch and someone sighed really heavy. I want to hear more but they're dead quiet at this hour.

Finding it hard to believe the antenna in the attic isn't 10x better than a 18" mag mount sitting in my closet on a the side of a PC for a ground plane.

Thanks so far

Could be some kind of signal overload issue also.

I listen to the train crew during my commute, and if they're talking to dispatch on 160.320, the scanner may stop on 160.230 (the road channel) and I'll get a bunch of static. There could be something else transmitting on a nearby frequency that's interfering with 423.625. Having a really good antenna setup makes this more likely. Switching to the crap antenna attenuates the other signal enough so it isn't interfering any more.