MDC/Date falsing on Repeater channel

[abrasowski]

This has been going on for a while since my work has had our system in service, but just recently I decided to ask to see if any of you know what this could be:

Our system consists of various ht1250/cdm mobiles operating uhf 478.xxx. I'm not sure of the repeater model because I haven't "opened up the locked motorola rack" that it is stored in atop one of our 8 story buildings, but- on our main channel, every once in a while data bursts will come over the air, sounding very similar to mdc bursts but shorter and perhaps may a say sounding a little like "trunkung data" mixed with mdc. It happens consistently for less than a minute, then stops. Then maybe 2 days/1 hour/a week later it happens again.

Any of you familiar with this? Is the the repeater falsing or one of our portables/mobiles in the field?
It unmutes all of our radios so I'm convinced it has to be coming from one of our radios or repeater with the right pl tones


Thanks in advance

[fineshot1]

Do you have more than one repeater in the same cabinet or in another cabinet in the same equipment room?

It sounds like you may be getting intermodulation from another close by repeater either yours or someone else's
repeater perhaps.

[abrasowski]

we do run 6 different repeaters with frequencies roughly within 10mHz of each other, however, I believe they are spaced at least 1 mile apart from each other.
One thing to note is that if repeater #1 is falsing or transmitting this unknown interference, repeaters #2, 3, 4, 5, & 6 may or may not have activity on them at the time, so its not "exactly when I repeater #- is keyed up".

Unfortunately we also have many hospitals/taxi companies located near by with their own systems set up.

[abrasowski]

...wanted to re-visit this topic. At work now and the system is acting up again, wanted to give you a more detailed explaination see if anyone else has experienced this. the sound happens commonly on lets call it "repeater 1" (47x.xxx) and is a consistent combination of a ticking and a beeping sound. It will go "tick, tick, tick, tick, tick" and continue for 20-30 seconds or so. Tonight it happened but stayed on for a good 5 minutes and we had to switch to a secondary repeater.
Also to note, every once in a while the tick tick tick will end with what sounds like an mdc type burst.

Totaly clueless on this, radio shop which installed all of our communications and repeaters is called everytime it gets so bad we can't conduct normal police comms, and by the time they get here, it stops. They are clueless as to what is going on.

Any help is appreciated

[fineshot1]

Do you have any way to record these sounds and post it either here or some place we can access it?

It might help if we could hear it.

[linkinpark9812]

I assume it isn't a trunking system due to the model radios used.

Now does this just happen on the output frequency? Or is it some un/intentional interference going to the input frequency causing the repeater to kick on.

If you got a PL on your input, I wonder if it is deliberate? But with the ticking noises and such, that wouldn't make much sense if it was intentional. Any nearby frequencies used without a repeater system (aka construction radios) on a nearby frequency with the same PL or something?

Could just be a repeater problem tho...

[Pj]

How close to NYC? NYC's new UHF TRS is a mixed mode system up in that range. I have also heard another fire department on one of the FDNY tac channels (don't remember which one offhand).

First step would be to have the repeater serviced, and then also run a FCC query on what is licensed adjacent to your repeater inputs and go from there.

[Bill_G]

Your radio shop should listen to the channel, and try to identify the offender as it occurs. Most likely caused by intermod, but with durations of 5 minutes, maybe not. They will have to listen to the noise, then scan the area, and listen for that same noise on every carrier they find. They'll just have to dog this out.