SERIOUS Quantar interference Help needed

[allplowedout]

Click this sound file to download or listen to the noise: http://www.savefile.com/files/3685961

Have a UHF quantar repeater station emitting this noise every so often, initially thought it was malicious interference, then believed it to be the control board from the quantar, in which we swapped it out. Today the unit again made a noise, of which I am going to try and attach a small wav file of it. If I can't post the sound file, anyone who is interested in hearing the sound, can email me at [email protected] and I will email them the sound clip of it.

I've got this as a case with motorola system infrastructure support group and they've got nothing to report yet. Batlabbers, wanna tangle with this?

Thanks for reading.

[allplowedout]

http://www.savefile.com/files/9352069

hERE'S link to another sample of this noise

[batdude]

sounds like some kind of interference on the wireline to me.

is this a remote / tone / dc whatever controlled station?



doug

[allplowedout]

Hi Batdude, Yes it's got a wireline control, running four wire via two seperate RTNA lines.

Other than checking levels on the lines, what would be a better way to ascertain the source of this problem. Usually or most of the time, it's been brought on by someone keying up to talk, once they de-key, noise starts, and goes beyone the length of the setting on the time out timer.

I think there may be different settings on TOT for wireline and different settings for over the air TOT.

We've checked all the settings and I don't like the fact that we're inable to identify a source of this, nor can out vendor who provided & installed it at this time. We believe they're quite competant in the system and it's troubleshooting, it's just that we're exhausting our patience with this and it's public saftey so we're either gonna put up a temp unit we have access to or ask that it be returned to motorola, BUT since it MIGHT be a wireline issue OR a malicious issue, we're not sure what to do.

Discounting malicious is that hte noise continues beyond the length allowed of OTA transmissions by a longshot...

[FMROB]

Never experienced that noise with the uhf quant.. That sounds horrible. What does the station do when disconected from the wire line.. Rob

[EKLB]

Air condioner system at the site running during the noise by chance ?

Possibly interference from a bad capacitor in the air conditioner compressors start up circuit and bleeding back onto the electrical .

Generator back up running ???

Just a wild qeuss but ive run into problems some what similar to yours but not as horible as yours sounded .

Might try turning off other electrical items as a start in locating it if its electrical related.

EKLB

[allplowedout]

I've given deep thought to many of those sources you mention...

I've had this problem, WITH a large APC unit inline and OUT of line, this maching has battery backup in the form of two 12volt batteries underneath it as well.

No wireline tests have been done up to this point, however unless someone here has a better alternative, I was told by the shop who services us that if the problem could not be located, the unit will be taken to the shop for observation and we'll be putting a spare PDR repeater there as a temp backup.

Anyone have any other thoughts on how I could check what might be causing this, since the shop does not seem to have a clue? I know they're pretty good with radios and such, I just don't think that they have a clue where to go from here after swapping the board, NOR do I have a clue what else could be doing this. It came out of nowhere about3 weeks ago, and this system has been online for over 6 months.

The quantar was installed 6-7 months ago, but without KNOWING that the problem is IN the quantar, we don't have a leg to stand on with motorola do we?
I appreciate everyone's time in reading this.

[Bob W]

That sounds like feedback, complete with digital processing delay. My bet would be that one of your two wirelines doesn't have enough return loss - that is: the audio from the receiver heading out to your remote makes a round trip back into the transmit audio input of the quantar. Could be a telco package (a 2-4wire hybrid) has gone bad, or no termination in the two wire remote, or if 4 wire all the way to your remote, a problem in the remote. You need to lift the transmit (wireline) input to the quantar, and listen to what's coming back on the phone lines. If you hear repeater traffic on one of the lines(what's going out is coming back), that's your culprit. Unless the quantar is hearing itself onthe rf side - intermod, etc., that noise is not going to be created internally.

[d119]

That sounds like feedback, complete with digital processing delay. My bet would be that one of your two wirelines doesn't have enough return loss - that is: the audio from the receiver heading out to your remote makes a round trip back into the transmit audio input of the quantar. Could be a telco package (a 2-4wire hybrid) has gone bad, or no termination in the two wire remote, or if 4 wire all the way to your remote, a problem in the remote. You need to lift the transmit (wireline) input to the quantar, and listen to what's coming back on the phone lines. If you hear repeater traffic on one of the lines(what's going out is coming back), that's your culprit. Unless the quantar is hearing itself onthe rf side - intermod, etc., that noise is not going to be created internally.

I'm with Bob on that. Pull the wireline and see if the noise goes away... If it's tone controlled, guard tones, etc may be leaking back through the wireline and keeping the thing keyed up. With the DSP delay, there's enough delay to induce feedback instead of the "hollow" or "railing" noise you'd hear on a non-delay system.

Regardless, please keep us posted.

[allplowedout]

Problem was determined to be from the Quantar itself, problem went away when a suit case repeater was installed as a temp.

Motorola has replaced the unit with a brand new one.

Will post again if problem resurfaces, although I don't think it will.

Clue that led us to lean more towards the unit failing itself was the lack of the TOT operation when the noise happened.

Thanks to those who replied.