Batboard

This noise just started and it is getting to be disruptive. I'm puzzled. Everyone is puzzled.
http://www.nmvfc.org/rfnoise.wav

It might help if you spill a little info on the source of this noise as you call it. Is this
from a conventional system or a trunking system? I gather that your using a tone
squelch of some sort. Hard to tell what is going on without some more details.

It sort of sounds like some intermod, but would like a few more facts before I make
any bets on it.

Jim

nmfire10 wrote:This noise just started and it is getting to be disruptive. I'm puzzled. Everyone is puzzled.
http://www.nmvfc.org/rfnoise.wav

That's an odd one, never heard it before. Sounds like someone else's stuff has wandered onto your input frequency. Perhaps some sort of data?

We had an issue with a business out here using an LTR system, and one day when they'd land on a certain channel they'd get clobbered by data. Turned out it was most likely a survey team in the area that had equipment on the same frequency as the repeater input.

You're obviously public safety, so this is an unlikely explanation, but just an example of what CAN happen.

that almost sounds like someone is sitting on a transmit button and don't know it then the tot shuts it off. it don't sound like data to me. what kind of system is this?

Sorry, I was in a rush before. It is a UHF conventional voting system. Only the main receiver up on the roof picks it up. The two indoor receivers do not get this. The system uses a DPL. We've had intermod issues before but nothing like this.

Since you guys have all the wonderful wiring jobs in your backroom... I'd almost say some sort of ground or connection problem. Just has that "green wire is touching something it shouldn't" kind of sound.

PJ, you are thinking the town's PD radio. This is the evil empire in New Haven. All the radio circuits there are immaculate works of art.

what kind of antennae is it? is there any way something hasn't rubbed or chewed it's way thru some of the jacket on the cable. it still don't sound like data or an adjacent channel, there isn't the slightest sound like a voice or even a digital sound, it's just open

Is the noise incident with the TXer keying due to a valid input? Or does the noise pull the TXer up by itself?

I'm almost thinking TX RF getting back into the receiver and doing odd things.

Possibly antenna generated IMD products?

It sounds like two DPL streams mixed together to me. But, how, audio feedback like someone else mentioned earier?

Right after the mobile unkeys, there is a wire line TX tone sequence and then the noise. SO, something that is keying the transmitter via wire line.

That something keying it via wireline is the voter. It indicates that the main station on the roof, (Quantar), is the one receiving it.

nmfire10 wrote:That something keying it via wireline is the voter. It indicates that the main station on the roof, (Quantar), is the one receiving it.

Maybe if you'd try answering all the questions posed to you, you might receive better help...

nmfire10 wrote: This is the evil empire in New Haven. All the radio circuits there are immaculate works of art.

bwaahaha! They would be the only immaculate works of art in dirty haven.

Let me see if I have the basic facts of the situation from the various bits of information.

As I understand it, the following facts are known:

It is a receiver voting system.

The interference is on the "self" receiver, not a remote.

The interference appears only after a mobile has keyed up the repeater.

Based on the above, I have heard a similar situation with the voter "hanging" on a noisy lease line
after a received signal. In this case, it is the "self" receiver with the problem which rules out a noisy lease line.

I would suspect RF from the repeater is getting into the receiver or voter audio and causing the problem.

new haven PD has also been getting lot of noise as well. also out UHF rpt at ui is barley usable due to a data stream on our channel

Sorry my responses have been short. I haven't had much time to spend on here. This facility is only my part time job now and I only get calls when something is screwed up. I'm not there all day to trace everything out and troubleshoot. I haven't been on the roof to investigate anything but the MSS has. They are as puzzled as me.

As far as I know, it only happens when something legitimate keys up the station, either a mobile or the dispatcher. The voter is located in the comm center so even the Quantar's receiver goes through wireline to the voter and then back to the transmitter. The other receivers are all indoors.

I'm with you guys that it is something within that is doing this and not an external source of IM or data. There is no hint of voice or data. Just this crap noise. I was hoping someone here would have heard this noise and say "Yes, I've heard it and it was __________."

Since you say it is known the apparent source is the Quantar receiver, I assume that is from observing the voter panel showing that receiver is voted for the duration of the noise.

Has anyone listened to the local audio right at the Quantar receiver to see if the noise is actually received vs something happening in the voting encoder, wireline or voter panel?

I have heard similar noises from a voter hanging after a transmission due to bad receiver voting encoder or voter panel cards or bad audio lines. But, that does not rule out something getting into the receiver until you listen to eliminate that possibility.

If the receiver is not the problem, monitor the wireline between the receiver voting encoder and the voter panel for noise, proper voice and tone levels etc. If everthing is proper and the noise is not heard going into the voter panel it is probably a bad line card in the voter panel.

This probably isn't of any help, but that noise sounds just like the "mystery" noise which drifts through the 10 Meter FM amateur band when the band is open, and has for years. Some of us believe it's an industrial high power induction heater located somewhere in the US. The sound is sort of like a carpenter's power joiner/planer.
How it would get into a system with CTCSS on the inputs is a mystery, unless it's getting in on a leased line as mentioned.

Hello :
Cant say i have any experience with a voter type of system.
But i have had troubles with a ctcss comunity repeater that closely ressembles this senario.
It too only put the noise out after being keyed up for a bit but not when keyed up for just a short message.
But it would unkey itself after the mobile unkeyed as normal.
Turned out that when keyed up long enough or the heat of the day was on that the cooloing fan produced the electrical noise due to bad bearings causing the armarture inside the motor to spark badly from the brushes.
Ill admit the noise you provided didnt sound quite the same as i remember on this one but it makes me wonder if you too might have something similiar.
Maybe try unplugging anything you can and see .
Anything else electrical close by that shares the same power source ?
I dont know what it is eigther - but it will be interesting to see what actualy is causing the noise.
Satelite

It sounds like a short to ground of one side of the telephone line or a leaking lightning arrestor.

I have a the voter's TX pair connected to our audio recorder from a previous troubleshooting mission. Perhaps I'll switch that over to the receiver's pair and see what I get. The I can compare what the receiver itself is spitting out vs what is getting transmitted.

It sounds like normal RFI interference that I hear when I'm near a strong source, like a fast food place. You might try setting your squelch levels higher to eliminate the source of interference. I get this same sound on my mobiles when I'm in the proximty of a McDonald's. Wendy's. etc. I set my squelch to 7 to eliminate the problem. Problem solved. My 2 cents worth...

Jim

Ok, this on a $16,000 Quantar on the roof of a 14 story building. I don't think it is a McDonalds drive-through and this is a little more complex than "set the squelch for 7".

My two bits worth:
I think that I heard something about 3/4 of the way that sounded like data.
But then you indicate that this is a DPL system. This only happens when the transmitter is keyed.
Sounds as if you are having intermod with your own transmitter. That is how the receiver stays unsquelched.
However, I would expect audio feedback in the form of a screech, but then perhaps the DSP in the Quantar inhibits this.

Another possibility is that you have a bad telephone cable with cross talk, perhaps you are getting 2175 guard tone from some other circuit causing hang up of the transmitter.
This is a reason for using the "Alternative Status" tone, 1900 Hz.
I have had problems with transmitters hanging on due to cross talk from another system.

A case history:
The Governor's radio repeater was located on a hospital roof, worked fine for years until it developed a problem similar to yours with a screech. Seems that the roof had just been re done with nice shiny copper flashing with galvanized roofing nails holding it down. There was an FM broadcast station down the block. That roof had every mix imaginable, all those dissimilar metals were biased on by the broad cast station.
The problem cleared when the FM station moved.

You did not elaborate on the voter but due to it using status tone I would assue it would be of motorola quality. I would look for an RF interference, If this shows clean then you may have a inbound line issue which can be ruled out with the listen on the Rx side of the Quantar. When I listen from 25 to 32 seconds the noise changes pitch and again after it votes audio from the MDC ID and then from 32 to 35 seconds till it ends. It sounds of intermod which of course is not common on UHF, yeah right. Do you have a television station near by that may have recently switched to DTV? they do not create noise now do they.

Also, how often does this problem occur, if it is frequenct and timable, there is another direction to go, if its at its leasure then I would do your recording so you can tell if its coming in on the RF or if its on the line. If you are using cat5 near some dirty router then you may find this before long.

I am a ways south of you but if you need help just ask.

CoM

This sounds a bit like a problem we had once...turned out to be a punch block fail where the audio routed between the SpectraTac and the microwave channel bank. Intermittent shorted pins or something...

We're having a similar problem on a UHF analog voted system that I work on (4 TX simulcast sites, about 13 RX sites). I'll let you know if I find anything with it....

I finally got in there to start evaluating and asking questions.

It seems to be random. Some days it shuts the place down for hours and hours on end. Some days it doesn't do it at all. Some days it does it a few times. No pattern I can see. I confirmed it is not related to precipitation or temperature. The noise starts only after the station is keyed up either by the dispatcher or by a unit in the field. It is not specific to one or the other. It does not start on its own, it only happens when the station is keyed. It will remain blasting out until it stops on its own meaning it has our DPL in the mix. This is screaming some kind of intermod because where else is it going to get our DPL from.

I connected a spare recorder channel to the RX RTPA pair but the pilot tone is way higher than I can set the VOX level for. The channel will record 24/7 which isn't going to work. I left it connected so I'm there when the problem is occuring I can turn it on and let go. Just listening to it the few times I heard it while I was there, I think it is definitely RF and not phone lines.

nmfire10 wrote: I think it is definitely RF and not phone lines.

That question can be answered positively IF you hear the noise listening directly to the Quantar base receiver audio, not monitoring the line.

If the noise is heard in the receiver, it is an RF problem. If not, it is a problem with the phone lines or voting and control circuits.

Based on what you describe, it sounds like an RF problem but you need to be sure before you get into the complicated effort of tracking down an intermod mixing source.

I'm leaving instructions for the dispatcher to call me right away the next time it gets bad. That way I can make haste in there and see it in person. They are also wirting down the date and time it happens so we can evaluate outside influances.

Not this will probably make any difference, but I power cycled the quantar last night as well. I'm pretty sure nobody has tried that yet. Couldn't hurt.