Need help identifying interference tones

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adlertom
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Need help identifying interference tones

Post by adlertom »

Below is a link to a wav file of some tones that have been intermittently received on a police repeater system that I do some maintenance on:

http://personalpages.tds.net/~adlertom/tones.wav

The system is a 4-site voted analog conventional VHF repeater. The tones are being picked up by one of the receive sites. PL is in use. The site is connected to the voter via a leased telco circuit.

I don't know if it's perhaps crosstalk from another telephone circuit, or if the noise is actually coming in on the receiver. It sounds pretty clear and strong, and usually happens at night.

Thanks in advance for any ideas on what this might be.

Tom
Will
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Re: Need help identifying interference tones

Post by Will »

Packet data.
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Bill_G
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Re: Need help identifying interference tones

Post by Bill_G »

The customer needs to monitor the comparator to determine which receivers it is coming in. If it is just one, and always the same one, then it could be telco problems. If it is heard by two or more receivers, you get to fox and hound.
cobra949
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Re: Need help identifying interference tones

Post by cobra949 »

SCADA Sniff around municipal sewage lift stations (no pun intended), water towers, industrial facilities, substations. Depending on where you are there could be lots of it. I have run across this problem twice in 30 years. One was a dirty transmitter feeding a nice little yagi pointed right at the SO repeater site. As above, isolate what receiver, is it off air or on the wire line? If it is off air and strong enough you may be able to see is on a service monitor and figure out what freq. it is on as what you are hearing may be a spur and not the center freq of the signal. Then just drive in ever widening circles or get a small yagi and try and triangulate the location. This could, will take some time. If you are lucky it is crosstalk on the wireline and you can just pass it off to the phone co. Good luck with that one to.
adlertom
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Re: Need help identifying interference tones

Post by adlertom »

Thanks for the advice so far. It is only coming in on one RX site, and that site is connected via Telco wireline to the voter. None of the other 3 RX sites are picking it up.

Today the phone company changed that site to a different wire pair, so we'll see if that helps. It would be great if that fixed it, but I'm still thinking that it's more likely to be an intermodulation mix. It's very intermittent, so tracking it could be difficult.
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abbylind
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Re: Need help identifying interference tones

Post by abbylind »

If the change in telco lines doesnt cure your ills and if this a UHF system by chance, I'd look for a Garmin surveying system in the area. Surveryors have been known to "dial in" freqs used by other agencies for their data downloads. Real annoying and a fox hunt is tough as they move the transmitter frequently.
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kb4mdz
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Re: Need help identifying interference tones

Post by kb4mdz »

adlertom wrote:Thanks for the advice so far. It is only coming in on one RX site, and that site is connected via Telco wireline to the voter. None of the other 3 RX sites are picking it up.

Today the phone company changed that site to a different wire pair, so we'll see if that helps. It would be great if that fixed it, but I'm still thinking that it's more likely to be an intermodulation mix. It's very intermittent, so tracking it could be difficult.
Don't see how changing to a different telco pair will help if the signal is coming into the receiver; seems like a waste of time & effort.

How long has it been going on? Is it constant, or intermittent? Daytime only? (this might point to the surveyors idea, unless they just leave their GPS base on all the time)

And can you put a service monitor antenna port straight to the antenna at that site? I'm assuming it's a receive only site. This way you can see the strength, whether it's on freq., deviation, etc.


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d119
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Re: Need help identifying interference tones

Post by d119 »

That is Motorola INTRAC equipment you are hearing, no doubt about it. Supervisory control and data acquisition (SCADA) stuff, as previously mentioned.

There is a central and a remote that are talking to each other. You can tell there are two stations due to some overlap typical of this type of situation, represented as the heterodyne you hear briefly after the tones.

JPS SNV-12 voter eh? ;)
adlertom
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Re: Need help identifying interference tones

Post by adlertom »

Thanks Chris. How confident are you that it is a specifically an INTRAC brand modem?

An identifiable pattern has emerged with the interference. It more often than not occurs on a Tuesday morning at 2:00 AM. Whatever system this is probably does a self check of all sites at that day/hour. So, at least now I have a time where I can schedule myself to be at the site with service monitor.




d119 wrote:That is Motorola INTRAC equipment you are hearing, no doubt about it. Supervisory control and data acquisition (SCADA) stuff, as previously mentioned.

There is a central and a remote that are talking to each other. You can tell there are two stations due to some overlap typical of this type of situation, represented as the heterodyne you hear briefly after the tones.

JPS SNV-12 voter eh? ;)
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Bill_G
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Re: Need help identifying interference tones

Post by Bill_G »

What a weird time and interval for a SCADA system to do some polling.

There are two modes: polled, and report on exception (or sync and async). A master polled system is constantly chattering. The master transmits queries to each remote unit one at a time, and they respond with their payload (whatever it is). A report on exception system is quiet until (A) a remote unit has an alarm, change in condition, etc, or (B) a schedule forces a remote to report to verify it is operating (usually daily).

A once a week link health report is a really long interval suggesting it is the remnants of an old system that has been abandoned but never turned off. I would do an FCC license search looking for expired licenses with low ERP most likely registered to a municipality or county. Since it is only heard by one receiver, you could narrow the search with a short radius from the lat/long of that receiver.

It could even be the city you are doing work for. ie: ten years ago they used the channel for the sewer and water department SCADA, switched to DSL or wi-fi, and gave the license to the PD. Now, there are two lonely remotes looking for the master. On the other hand, if that were the case, this would be an on going problem for years.

And maybe it was a problem. Nobody noticed because the receivers are PL protected. But, as the remotes aged, their power supplies developed big ripple that shows up as multiples of 60hz that can open 118.8 or 179.9hz. I've seen it happen. The SCADA logic keeps working because it runs off a well regulated 5V supply derived from crummy 12V, but the radio suffers each time it keys up.
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wx4cbh
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Re: Need help identifying interference tones

Post by wx4cbh »

A great number of INTRAC systems were sold to golf courses, nurseries, and other large landscape interests who use it to control irrigation systems, so there's also the possibility that's why you are mostly or only hearing it at night. I can think of several that we installed before I retired that are still in service and working. Considering how long INTRAC's successor MOSCAD has been in play, there's a good possibility that the interference is simply a result of the suspect equipment being old and in need of radio/feedline/antenna maintenance. Considering its potential age, and if it is still all INTRAC equipment, I would also strongly suspect it may not be narrowband compliant either.

With all that said, MOSCAD was designed to handle the INTRAC scheme in mixed systems that had MOSCAD additions and replacements in the period where INTRAC was no longer available, so don't count out the possibility that the whole system may now be MOSCAD but still using the INTRAC scheme.
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d119
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Re: Need help identifying interference tones

Post by d119 »

adlertom wrote:Thanks Chris. How confident are you that it is a specifically an INTRAC brand modem?

An identifiable pattern has emerged with the interference. It more often than not occurs on a Tuesday morning at 2:00 AM. Whatever system this is probably does a self check of all sites at that day/hour. So, at least now I have a time where I can schedule myself to be at the site with service monitor.
Actually, I was tired when I made that comment. I don't think it's INTRAC at all.

Last time I heard this, it was being used to control sirens... CompuLert is the equipment type that was identified when I last heard it on KB9UKD's page... Have a listen:

http://www.kb9ukd.com/digital/compulert.wav

Also see:

http://www.americansignal.com/products/ ... d-control/

Now that I'm awake, and have the above information to offer you, I'm SURE of it.

Did I identify the type of comparator being used (SNV-12) correctly? ;)
adlertom
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Re: Need help identifying interference tones

Post by adlertom »

Chris,

Yes, I actually had already communicated with Gary (we know each other) and he initially identified it as Compulert as well. I contacted American Signal and they don't have any systems in our area. However, according to Gary, it could still SOUND like Compulert without actually BEING Compulert, since several SCADA equipment manufacturers might use off-the-shelf modems from the same supplier in their end products.

Yes, it is a JPS SNV-12. I had communicated with you several years ago about continuing to use an older Spectra-Tac for this department's system, but the JPS solved a lot of problems. So, we just went with that. Nice voter. What made you ask?

This is a VHF police system, and the PL is 167.9 Hz. I've heard of the AC power issues with 118.8 and 179.9 PL you mentioned, but never with 167.9. I'm wondering if this is a 2A-B mix, but not sure how it's getting past the PL.

All of the SCADA I've identified so far in the area is on UHF. So, 2A-B would be an odd mix to have an end result of 153.995 w/167.9 PL.
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d119
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Re: Need help identifying interference tones

Post by d119 »

I can just "hear" that it's an SNV-12. Wanted to make sure my ear was still properly tuned :)

We put one of those into one of the University Police Departments about a year ago. Really smooth transition and it sounds great! Since DIGITAC is no longer in production, it's the natural first choice for an analog comparator. MLC 8000 just seems too complex (and expensive).

Agreed on the Compulert "audio" not necessarily being actual Compulert equipment. Could be a generic FSK modem.

What kind of receivers are you using at the sites? Is it possible that the receiver in question has fallen out of PL mode?

We had some issues in the past with MTR 2000 stations (receivers AND transceivers) falling out of PL mode. This created a real mess until we narrowed it down.

The fix was a firmware update and a "fresh" codeplug being loaded into the stations. The particular ones I had trouble with were VHF stations.
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