Interference Sound on UHF Freq

eteves

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If this thread better belongs somewhere better, moderators feel free-

I'm listening to a local business on one my of my Motorola P25 handhelds but I've cross tested this frequency on a few of my other radios that include Kenwood and the same thing happens where, ever so often, an interference sound (I'm guessing) comes through that sounds a lot like a semi truck's Jake Brake - if you've ever heard one, then you probably know exactly what i'm trying to explain... Very loud though.

This is on a 464.1875 Freq
Works through one repeater that is on-site of the business with a PL tone
And there's only one repeater for that frequency.

In addition to that, which is their main, operations channel, they also have a maintenance/enginerring channel that uses another repeater that is also on-site with frequency 464.225 .
But I'm hearing this sound on their primary channel - haven't tried to see if I get the same thing on the Maintenance Freq.
Only happens when no one is transmitting - I'm guessing that because I only hear it then, given the fact that when they are talking, I can hear them and understand very clearly but there is some static as they use analog and I'm this far from a UHF repeater (distance details below). I also know they use Kenwood radios if that makes any difference.

I'm hearing this sound from my house which is about 8 miles away give or take from the repeater no line of sight, which isn't super elevated (mounted on the roof of a two story commercial bldg with like 12-14 ft ceilings.) So it's not on the ground but its also not on a skyscraper either.

Both are 15 Watt repeaters per FCC license search.

Just guessing here, not sure if someone is stepping on someone else's transmission or the fact that maintenance or even some other un-identified source could be cross interfering.

Pretty sure they are transmitting Narrowband as well - I know there was a mandate that the FCC put our a while ago for VHF, not sure if it includes UHF or not.

Maybe someone might know on here or might just have some input..

Thanks in advance
 

Ubbe

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I'm listening to a local business on one my of my Motorola P25 handhelds....
...Works through one repeater that is on-site of the business with a PL tone....
....Only happens when no one is transmitting....
So you have a radio that are programmed with a PL tone to the RX frequency and the site are transmitting using a PL tone
and you only hear that interference when the site isn't transmitting and you hear the same inerference on you other radios, that also have PL controlled squelch programmed to the frequency? Is that correct?

/Ubbe
 

TampaTyron

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Probably MOTOTRBO co channel or intermod at the same site. What other repeaters are at the same site in the same band? TT
 

a417

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You are hearing what is probably a digital signal on the same frequency, in the plainest sense.
 

eteves

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Probably MOTOTRBO co channel or intermod at the same site. What other repeaters are at the same site in the same band? TT
Only two repeaters that are on-site - total as far as I can tell through FCC Database Search. So if there are in fact any more, they aren’t registered. Just to add, I live in a small city and know that there are also no close by repeaters that are in that band. All the law freqs for this city are in VHF band also with Kenwood radios. City operations has a few UHF but their repeaters aren’t close to the site.
 

eteves

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So you have a radio that are programmed with a PL tone to the RX frequency and the site are transmitting using a PL tone
and you only hear that interference when the site isn't transmitting and you hear the same inerference on you other radios, that also have PL controlled squelch programmed to the frequency? Is that correct?

/Ubbe
Correct.
Also tried removing the PL and still same.
 

eteves

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I did forget about DMR sounds on analog and know that could possibly be it so I could probably agree to settle with that.
Thanks for the input!
 

Ubbe

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So you have a radio that are programmed with a PL tone to the RX frequency and the site are transmitting using a PL tone
and you only hear that interference when the site isn't transmitting and you hear the same inerference on you other radios, that also have PL controlled squelch programmed to the frequency? Is that correct?
Correct. Also tried removing the PL and still same.
Double check your programming on the radios as if you have the squelch under PL control it shouldn't open for other signals than the correct PL.
Some scanners might still open up the squelch on a strong modulated data signal like DMR but not radios and especially not on several different brands of radios.

In Motorola radios programming software you sometimes set the squelch action in a personality function and that personality must be refered to in the channel to be actually in use.

/Ubbe
 

eteves

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Double check your programming on the radios as if you have the squelch under PL control it shouldn't open for other signals than the correct PL.
Some scanners might still open up the squelch on a strong modulated data signal like DMR but not radios and especially not on several different brands of radios.

In Motorola radios programming software you sometimes set the squelch action in a personality function and that personality must be refered to in the channel to be actually in use.

/Ubbe
Ah, that would also make sense. I'll look through the codeplug in the prog. software and see if anything looks off in that sense. Thanks for that input.
 
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