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CDM1250 Squelch issue

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Jay G.
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CDM1250 Squelch issue

Postby Jay G. » Sun Mar 08, 2009 3:21 pm

Hello All!

Here's the situation: 2 LOW band mobiles with NO PL enabled (countywide system) installed in a rack at HQ for use with our main base station. Both radios for no apparent reason begin to squelch uncontrollably on various frequencys, not always on the same frequency or at the same time. Our radio guy seems to feel that the radios are attempting to decode something, and that they're working very well. He is afraid to change any settings, as he doesnt want to de=sense the recievers. I am going nuts with nothing but static playing throughout my building.

Any suggestions??? I'm getting desperate.

thanks!
Jay Goldmark, EMT
Ex-Captain, Woodmere Vol. Fire Dept.
Fire District Communications Supv.
KC2ZHI Amateur Radio Operator
Licensed Master Electrician
Owner, Top Class Electric, LLC.
Woodmere, Long Island, NY


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HLA
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Re: CDM1250 Squelch issue

Postby HLA » Sun Mar 08, 2009 3:52 pm

it sounds like the problem isn't your two radios, they are just recieving what's coming over the frequency like they are supposed to, it sounds like your problem is with what's doing the transmitting? and if it's doing it on various frequencies on the same band whatever is transmitting the static is very very close to the recieve antennae for those two cdm's? what's been changed or added since this has started happening?
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Re: CDM1250 Squelch issue

Postby Jay G. » Sun Mar 08, 2009 5:05 pm

I agree that they are recieving correctly. I think most of the problem is that they are recieving signals from great distances, much further then what we need or want, but since our county doesnt use PL on these channels, we have no way of limiting what the reciever picks up....
Jay Goldmark, EMT
Ex-Captain, Woodmere Vol. Fire Dept.
Fire District Communications Supv.
KC2ZHI Amateur Radio Operator
Licensed Master Electrician
Owner, Top Class Electric, LLC.
Woodmere, Long Island, NY


"Enjoy Life, it's not a dress rehearsal !!!"

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jackhackett
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Re: CDM1250 Squelch issue

Postby jackhackett » Sun Mar 08, 2009 5:08 pm

Here's the problem, in general the lower in frequency you go, the more interference there is, so low band gets it more than the other bands. Other transmitters at the site, computers, monitors, automobiles, flourescent lights, and lots of other electrical devices can cause interference on low band which will cause a radio to break squelch.
This interference can happen over a broad range of frequencies.

At certain times you can also get "skip", which are radio signals from sources usually too far away to receive, but which come in due to atmospheric conditions.

Using PL will keep the radio squelched, which makes it less annoying to listen to, but it doesn't take away the interference, the radio will still be picking up the signal, you just won't hear it through the speaker.

I'm not sure what your radio guy thinks the radios are trying to "decode", messages from aliens maybe?


Your options...
1) Find out what's causing the interference and eliminate it if possible
2) Turn up the squelch settings in the radios *
3) Convince the entire county to use PL on those channels (good luck)
4) Live with it
5) Career change


* adjusting the squelch can help if the interfering signal is weaker than the signals you want to hear. It sets the signal level needed to unmute the audio, if too high you can miss calls from units in the fringe areas, if not high enough it won't eliminate the stuff you don't want to hear... it's a bit of a trade off, and if people's lives are at stake you want to err on the side of not missing calls.

RKG
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Re: CDM1250 Squelch issue

Postby RKG » Sun Mar 08, 2009 5:45 pm

Long distance diagnoses are really just guesses (and worth no more than that), but:

If you're saying that these radios are scanning multiple channels and appear to break squelch with static noise on different channels at different times, that implies that the noise source is local to the receivers, and probably not coming from a distant transmitter. My guess would be a clock chip in a computer or other CPU-driven device.

pfd radio
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Re: CDM1250 Squelch issue

Postby pfd radio » Thu Mar 12, 2009 7:48 pm

Jay,
I had the same problem with Low Band CDM's in Plainview and I just tightened up the squelch and it was solved.

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Pj
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Re: CDM1250 Squelch issue

Postby Pj » Sat Mar 14, 2009 8:45 pm

46.10?
Lowband radio. The original and non-complicated wide area interoperable communications system
Image

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nmfire10
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Re: CDM1250 Squelch issue

Postby nmfire10 » Sun Mar 15, 2009 5:27 am

I've had two CDM's that both had the squelch set stupidly close to being open all the time. Bumping the squelch sliders up only a few points fixed everything.
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