Signal Intrusion Frequency not in Database

[CalmWind]

I am having a signal intrusion situation with my Internet cable modem. The problem is being caused by a local Public Safety Trunking system but the frequency is not included in the Database listing for the site.

The frequency involved is around 807.00MHz but the database site frequencies are 851-854 Mhz. Since there are possibly 4 frequencies used by the Trunking system in the 806-809 MHz band, should they be included?

I have added one directly in my BCD536HP but do not yet have any results showing it is being used.

Thanks.

NAC 3B1, Denton County, TX, Plano, Allen, Wylie, Murphy (PAWM) P25

 

[mikewazowski]

Thread moved to General Scanning forum.

The frequencies in the 806-809MHz band are repeater inputs and are not necessary for monitoring a system.

 

[CalmWind]

OK, If it is an actual transmitting site instead of a mobile unit in close proximity, there would be nothing I could do about it affecting my Cable Modem....

As far as the Database, I will have to go back and recheck my earlier findings. I could swear I could not hear some transmissions on the primary channels but I could see the Spectrum Analyzer show activity on the repeaters. Maybe a little more experience with my new radio will help.

Thanks..

 

[KevinC]

Just curious, what leads you to believe something in the 800 MHz range is affecting your cable modem?

 

[mikewazowski]

OK, If it is an actual transmitting site instead of a mobile unit

You misunderstood. It's an input to the repeater so portables and mobiles would be transmitting on it.

If you think it's causing problems with your cable modem, call the cable company and have them check for ingress.

 

[CalmWind]

Just curious, what leads you to believe something in the 800 MHz range is affecting your cable modem?

I had been working on the situation for over a month. I started to put together sirens and the Uncorrectable errors, so I started watching closer.

After I decided it was signal intrusion, it had to be somewhere around 807.00 MHz so I got a Spectrum Analyzer and starting tracking strong signals in that band. When the Uncorrectable errors showed up on the Modem I was able to tie them the spikes, up around -45 dBm, to the errors. I was getting up to 100,000 to 200,000 uncorrectable errors on the one downstream channel. No other channels had errors.

Next I needed to know what was transmitting on those frequencies. So the Scanner was the next step and it showed the spikes were being caused by the Radio Traffic in the Public Safety area. I thought it was local because the Fire Station is about 150 feet away and police cars go by the house.

It seems the spikes at or just above 807 MHz and at or close to 808 MHz were causing the errors.

 

[mmckenna]

Cable modems are a Part 15 device, and they are supposed to tolerate a reasonable amount of "interference".

I agree, I think you need to talk to your cable company. Sounds like there is a problem with your drop. Bad connector, damaged cable, unterminated connection, etc....

 

[wtp]

so ? as i scratch my head...

you think the problem is with a trunking system and it is the low power input and not the repeated signal at higher power and you can't get the signal on you scanner on the low power input.
seems to me that it would be the higher power signal getting in.
the only other thought is that there is a weak spot on the cable shielding or a line repeater and it is picking up a car output when it drives and transmits close to it.
all in all i would call the company.

 

[CalmWind]

Cable modems are a Part 15 device, and they are supposed to tolerate a reasonable amount of "interference".

I agree, I think you need to talk to your cable company. Sounds like there is a problem with your drop. Bad connector, damaged cable, unterminated connection, etc....

Maybe "Reasonable" is the operable description. Most of the transmissions come in around -80dBm. The ones that jump to -60 to -45 may not be reasonable.

The thing that convinced me of the signal intrusion was the fact, out of 18 downstream channels, only the one was showing the errors.

If the intrusion/ingress takes place on the cabling on the house, there is no way I can shield that. I tried to shield the actual box but not having much luck.

Thanks for the response.

 

[CalmWind]

you think the problem is with a trunking system and it is the low power input and not the repeated signal at higher power and you can't get the signal on you scanner on the low power input.
seems to me that it would be the higher power signal getting in.
the only other thought is that there is a weak spot on the cable shielding or a line repeater and it is picking up a car output when it drives and transmits close to it.
all in all i would call the company.

I don't know how to track down where the problem is getting in. I have a snap on ferrite ring on the power cable. The cabling is RG6-U which I have recently replaced from the drop to the modem and no other connections.

Thanks

 

[ecps92]

Turn Off (unplug) ALL the other Electronic Devices in the House and see if it is still there.
That includes the TV, VCR, DVR, Microwave, laptops, monitors, wireless cameras, even the modem (if could be internal to the modem) and see if the Signal is still there

I don't know how to track down where the problem is getting in. I have a snap on ferrite ring on the power cable. The cabling is RG6-U which I have recently replaced from the drop to the modem and no other connections.

Thanks

 

[mmckenna]

Maybe "Reasonable" is the operable description. Most of the transmissions come in around -80dBm. The ones that jump to -60 to -45 may not be reasonable.

That's well within reason. A base station or even a mobile close in could cause levels like that.

The thing that convinced me of the signal intrusion was the fact, out of 18 downstream channels, only the one was showing the errors.

If the intrusion/ingress takes place on the cabling on the house, there is no way I can shield that. I tried to shield the actual box but not having much luck.

Thanks for the response.

I think you've narrowed it down well enough that you should try to approach the cable company. Be prepared for them asking you if you TV is on Channel 3 and all that B.S. I don't envy the challenge you have ahead of you. They'll likely send a field tech out that will be of zero help. You need a field supervisor to call in an engineer, likely.

The leakage could be anywhere in the system, not just your house. If the fire station has a cable TV drop and they've got an issue there, it could be backwashing into the system. Would be interesting to know if you neighbors are having the same issue.

We had an issue many years ago where we were getting all kinds of interference from our internal cable TV system. It was causing interference to aircraft on approach to SFO as they passed over head. FCC and FAA showed up and gave us a few days to find the issue or the entire campus would be disconnected. Took a full day, but they found a student dorm room where the cable TV cord from the wall to the TV wouldn't reach to the TV set. Someone had used a piece of scrap 16 gauge wire to "bridge the gap". That was removed and a proper piece of coax installed. The issue went away.

Cable TV systems can radiate a lot of crap, but they can also absorb it, too.

 

[CalmWind]

@ ecps92, the trace you see is a history and not an ongoing signal. The bursts may happen anywhere from no times to multiple times a day.

@ mmckenna, this is a internet modem, I do not get TV signals. I will contact TWC but I don't expect them to do anything since the modem is not resetting or dropping the connection. Maybe they will have some suggestions as to how to stop the intrusion, if it is even possible.

If the disruption was entering at another source, such as the Fire House, I don't think it would show it as an OTA signal? I suppose it could be both... and that is an interesting idea..

It may not be relevant, but the modem is actually a bridged Gateway with WiFi and phone. The Wifi is disabled and I disconnected the phone cable earlier and did not improve the situation.

I'll get back if TWC has any helpful suggestions.

Thanks.

 

[mmckenna]

@ mmckenna, this is a internet modem, I do not get TV signals. I will contact TWC but I don't expect them to do anything since the modem is not resetting or dropping the connection. Maybe they will have some suggestions as to how to stop the intrusion, if it is even possible.

If the disruption was entering at another source, such as the Fire House, I don't think it would show it as an OTA signal? I suppose it could be both... and that is an interesting idea..

It may not be relevant, but the modem is actually a bridged Gateway with WiFi and phone. The Wifi is disabled and I disconnected the phone cable earlier and did not improve the situation.

I'll get back if TWC has any helpful suggestions.

Thanks.

Doesn't matter. The network connection provided over a cable system uses the same coaxial cable as the cable TV service. They just put the internet carriers in some of the bandwidth that is not used for TV channels. Usually they use a band of frequencies for your uplink and a separate band of frequencies for your downlink. If I recall correctly, it's actually all channelized. Adding/removing channels from the uplink or downlink can change your bandwidth.

Since it's all the same coaxial cable coming from the local headend or from a local fiber to coax converter (somewhere on a pole/box in your neighborhood) any leakage into the system can get propagated through the system. If the interference is on one of the frequencies used by the cable system (either TV or internet) it'll get amplified by the system. The system usually can't tell where the signal is coming from, just that its in the passband of the amplifier/filters.
A leak into the system can get amplified by any/all line amplifiers, and can show up on your drop. Could be a leak letting stuff in anywhere around you. The cable TV technicians often will have receivers that will let them locate places where signals are leaking OUT of the system. A leak letting signals out can also let signals in. A police car/fire truck/ambulance/whatever driving past one of these leaks while transmitting would put enough signal into the system to cause issues.

Used to be a bad leak down the street from me. When I'd drive under a specific pole, the VHF radio in my truck would go nuts. Only did it within about 50 feet of this pole. You might be able to go sniffing around with your scanner in your neighborhood and see if you find a pace that has a lot of RF noise. Might try from 120MHz up to around 150MHz. Narrowing down the location of the leak (if that is the cause of the issue) would speed up the resolution. Cable TV companies can get in a lot of trouble if they have leaky systems.

I think there are some good suggestions from the others. Start shutting things off in your own home to rule out local sources. If that doesn't fix it, call your cable company and complain.

 

[mmckenna]

While not exactly what you are experiencing, this issue is seen with the newer LTE cellular systems.
Here's an interesting write up here:
http://www.denisowski.org/Articles/...ing and Resolving LTE Interference Issues.pdf

 

[mmckenna]

Ow, my brain hurts.
I work with a guy that does this stuff. I'm off work until the 9th, so I won't see him to ask him for details, but I did look at some of our documentation on the small system we run.

DOCSIS is the standard that is often used. May or may not be used by your system.
108MHz t0 862MHz is often used for downstream traffic. This would certainly put some interference possibilities around the NPSPAC 800MHz repeater input channels if the signals were getting from the radios transmitting into the public safety repeaters and accidentally, due to cable TV system leakage, into that system.
Sounds like what you may be seeing.
How those 800MHz frequencies are getting into the cable TV system would require a cable TV tech to investigate as there are many ways it can happen
Like I mentioned above, though, places where RF can leak -into- the system will also allow cable TV signals to leak -out- of the system.
Cable TV operators are required by the FCC to check their systems for leakage.

If (a BIG if) you can get through the customer service nightmare/horror show and actually talk to someone that will listen to you, you might be able to get a tech to come out and sniff around your neighborhood for a leak.

If they won't, grab your scanner and start sniffing around the VHF Air band for RF hash. See if you can narrow it down to a pole/box. Call the cable TV company again and tell them they have a leak. If they won't address it, a call to the FCC should make things happen. Cable TV links can impact aviation radios and navigation systems. This is a big deal if that is happening.

Of course it could be something totally simple, like a loose connection, so make sure you get all your stuff in line before calling the cable TV company.

 

[n5ims]

I am having a signal intrusion situation with my Internet cable modem. The problem is being caused by a local Public Safety Trunking system but the frequency is not included in the Database listing for the site.

The frequency involved is around 807.00MHz but the database site frequencies are 851-854 Mhz. Since there are possibly 4 frequencies used by the Trunking system in the 806-809 MHz band, should they be included?

I have added one directly in my BCD536HP but do not yet have any results showing it is being used.

Thanks.

NAC 3B1, Denton County, TX, Plano, Allen, Wylie, Murphy (PAWM) P25

WNWG614 (PLANO, CITY OF) FCC Callsign Details

The input frequencies (what the field units transmit on to reach the repeaters) are (second column):
5 806.15000000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.15000000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.17500000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.17500000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.65000000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.65000000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.67500000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.67500000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.96250000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 806.96250000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.15000000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.15000000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.17500000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.17500000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.65000000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.65000000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.67500000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.67500000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.96250000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 807.96250000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 808.27500000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 808.27500000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 808.30000000 8K70D1W MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX
5 808.30000000 8K10F1E MO 3600 0 35.000 33.16667 -96.75306 $ COLLIN TX

Those correspond to those listed in the RR database (input is 45 MHz lower than the repeater output). Since they're lower power and rarely stay in the same location, they're hard to track down, but if a unit keys up nearby a spot where the TV cable has a leak, it could cause issues. This would be especially true if they have overhead lines in your area. Squirrels like to chew on the cable and open it up for lots of leakage. A loose connection or the very common cutting off an unused feed (instead of properly terminating it) can also cause leakage.

 

[rfradioconsult]

Most cable operators put a carrier on their system around 136-138 Mhz with a beep beep tone so their techs can listen for the beep as they go about their daily activities. This is one way they can tell if they have a leakage problem which can also indicate a point where an external signal can affect the cable system.

I have ran across problems where the cable provider has had problems with a defective amplifier that has gone into business for itself and became an oscillator.

As others have said call TWC, I'm sure they can track it down, probably a common problem that they can find and fix in quick order.

 

[K5MPH]

Looks like you might have a cable leak down stream from you,I had almost the same problem and it was a leak at one of the Headers on the cable line down stream from me TWC is bad about fixing there leaky cable lines,good luck dealing with TWC you going to need it.............

 

[CalmWind]

I got out this morning and walked around with the frequency analyzer in the 120-150 MHz range. One signal at 124.285 at -64 dBm and one at around 142 MHz. Neither one changed as I moved in the different directions. I don't feel I have the ability to find a cable leak.

I had a unit sitting about 50 feet from the house and when he keyed up, I got a signal strength of -46 dBm, so I can sort of use that as gauge. There were no errors created from yesterday morning until this morning even with that strong signal because it was just below 807.00 MHz. But a strong signal came in this morning and 4000 errors were created.

I checked out the article about ingress/egress, but I suppose it is good I know what is causing the ingress. I feel that the problem is in the house due to the high power levels of close proximity mobile units, but a leak in the system is still a possibility.

I am going to contact TWC today, maybe they will be willing to look at least.

Thanks to all..

Edit: I do still feel some transmissions on in the 806 to 809 range are not carried on the Trunk System. So I am attempting to set up a Favorites list just for those....