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Horrible Interference on repeater

jcefd10

WWG1WGA
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Feb 13, 2017
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176
Good evening all.
I have a very general question here. Here recently we have been having some pretty bad issues with interference on one of our repeaters. We have 5 in the same hut, and only 1 is getting the interference.
We are running NXDN in 12.5 spacing at the moment at this site.
Something is transmitting on our FD/EMS repeater input frequency. It is such a strong signal, that the portables cannot key over it to key the repeater. Mobiles can, but only for a very limited distance. The other day when it was at it's worst, I think you could still get the repeater if you were no more than 6-8 miles from it. With my NX5200, I was standing at the base of the tower and was barely able to talk over it. Any more than .5 miles away, portables were useless. Our 911 could not talk over it either. They have a yagi on their tower around 150' pointed directly towards this repeater site so they usually have zero issues. We noticed it very badly last Thursday and I was hoping it was only atmospheric conditions, but again this morning it reared its head. I just made a quick run by the repeater to see if we were having the interference again and as suspected, we are. I was able to get a video of what is coming across, if that would help make sense of it all. All i can hear on it is some digital in the background. The foreground noise I have no idea.

I've contacted a couple of radio shops to see if any of the technicians could tell what was being received. We've searched the FCC site for anyone that may be within a distance to where the signal would be strong enough to keep us from being able to use our radios. We traced it down to 3 agencies in GA and one in AL so far that "MAY" be close enough to cause the interference. We contacted the closest of the ones and asked if they still had repeaters online using that frequency and they did not. I have programmed the input frequency in both digital and analog in both my portable and mobile radios with carrier squelch and you cannot hear the traffic from the ground, or at least I have not yet anyway. It never goes away completely it seems, just eventually gets weak enough we can talk over it for a while without interference.

Now the main question. How do I go about contacting the FCC to report the interference? I wasn't sure if there was a specific group you contact there, or a certain number to call for situations like this. Typically, I know nothing would need to be said or reported as some interference is expected, but this is leaving us pretty much dead in the water when the signal is coming across at its peak.


Apologies for such a long post! Thanks to anyone who stuck around to read completely. I would have not posted here but I'm out of ideas.
 
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AK4PY

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Jul 22, 2022
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Sounds like another digital signal. If it is persistent then you have an issue. However, I suspect it is just a band opening and it will go away when the enhanced propagation fades. Band openings happen frequently this time of the year and can last all day in extreme events. It isn't unusual to have a band opening every morning for a several week stretch this time of the year.
 

jcefd10

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I know for sure it's been persistent for 2 weeks, possibly longer. I have noticed over the past couple of months that sometimes during talking back and forth with 911 for a split second I'd hear someone else in the background, or the digital sound. I wrote it off as just an anomaly and forgot about it until it has gotten this bad.
 
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mmckenna

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I am a lineman for the county.
Now the main question. How do I go about contacting the FCC to report the interference? I wasn't sure if there was a specific group you contact there, or a certain number to call for situations like this. Typically, I know nothing would need to be said or reported as some interference is expected, but this is leaving us pretty much dead in the water when the signal is coming across at its peak.

But don't expect much. They are not going to show up and do all the hard work for you. You'll get better results if you provide as much detail as you can and give that to them. You need to do some work to determine exactly what frequency the noise is on. Is it on yours, or adjacent? If you can narrow down the source, that's even better. There isn't a huge team of FCC guys roaming the country doing this sort of stuff, what you usually end up with is one guy from the local office that comes out with a spectrum analyzer and will confirm what you see. Resolution can take a while.

I'm out of ideas.

I'd get your radio shop to come out and check things. Prove it's not your system, and that it's all set up correctly. They can plug in a service monitor/spectrum analyzer and get a better idea what's going on.

Sounds a lot like analog data. Ran into that on an analog UHF system years ago. Took weeks to track down. Finally found an irrigation system that someone had just randomly picked a frequency to use.

It probably won't be easy to track this down on your own.
 

jcefd10

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I have some guys from N GA coming down to retune a duplexer for a new pair of frequencies we got for our secondary FD/EMS repeater in a week or two. They said they'd be glad to hook the SA up and see what they could find. I had already asked if they'd sweep the main site while they were down just to make sure everything was in spec. I've already successfully contacted 2 of the 5 agencies that are licensed for 100+ watts on that frequency and are within 100 miles of us just to see if they've changed anything recently. So far, nobody has but all have been more than willing to help.
I knew the FCC wouldn't really be much help at all, so that wasn't really an option I'd considered unless all else fails and we just come up totally empty handed. If I can get my hands on a yagi, I'd love to at least see which direction it's coming from.
 

kb5udf

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Regarding tracking it down, you might want to consider sharing more information in your post like frequency(s) and location so that others can listen in and possibly assist you with tracking down the source of interference, if possible. You never know, you might get lucky.

I would add that it may also be helpful if you can upload a recording of the interference on your repeater input frequency. Perhaps someone can identify the noise.
 

jcefd10

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Program up your hand held with the repeater input frequency. Keep it in your car/truck as you drive around. You may find that you can narrow things down that way.

The irrigation transmitter that was interfering with our stuff was a 2 watt data radio. Doesn't take much if you have a high antenna with a good system.
I did that, so far I haven't gotten anything yet. I have it programmed on my mobile and portable.
Regarding tracking it down, you might want to consider sharing more information in your post like frequency(s) and location so that others can listen in and possibly assist you with tracking down the source of interference, if possible. You never know, you might get lucky.

I would add that it may also be helpful if you can upload a recording of the interference on your repeater input frequency. Perhaps someone can identify the noise.
Ok... THe frequency is 159.450, and it's located in Webster County GA.
There is an uploaded video just below the first post
Add the adjacent channels (+/-7.5 kHz) to your monitoring as well. I have a feeling it's going to be an over-modulated adjacent.
I thought about doing that when I added the freq to monitor. I've been trying to find an old analog Radio Shack scanner I used to have and can't find it anywehre. I was going to program it with several variants above and below and ride around with it in the truck. But that sucker ain't nowhere to be found. :LOL:
 

WB5UOM

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If the 1st one is you...and the other 3 are online or any one, good luck. I hvnt done the path on them but with the enhanced atmospheric conditions that are occurring, I can see your problem.
 

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12dbsinad

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First of all, welcome to the complete CF known as VHF here in the United States were somebodies output is another poor mans input. Anyway, check 7.5 up and down, I'm willing to bet this is adjacent channel problem and some sort of SCADA that TX's frequently. Jack a service monitor into the repeater antenna and you'll know in about 30 seconds, then go from there.
 

prcguy

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A simple test for intermod being generated inside your repeater is to slam a 10dB attenuator on the receiver port and see if the interference decreases and range increases.
Thats kind of a high level test that may not point to anything specific and it will attenuate both the desired signal and something high level and slightly off frequency that may be creating IMD Within the receiver. IMD generated in a device like a preamp, mixer, etc will go down 2dB for every 1dB you attenuate the offending input signal.

A more absolute way to determine if IMD is being generated in your receiver system is to inject a low level signal on the receive frequency with a directional coupler in the receive path right at the receiver, just enough for about 6-8dB SINAD. Then with a step attenuator at the antenna input where the problem would enter the system, add 1dB at a time until you see any improvement in SINAD.

If you see any improvement it should follow the 1dB of attenuation = 2dB of SINAD improvement. If there is no change in SINAD after a large change in antenna attenuation then the problem is not the receiver generating IMD.
 

techman210

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Absolutely agreed. But he didn’t seem to have any appropriate test equipment handy.

These repeaters need GOOD 6-cavity duplexers if they are at a high level “busy” radio site.
 

jcefd10

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If the 1st one is you...and the other 3 are online or any one, good luck. I hvnt done the path on them but with the enhanced atmospheric conditions that are occurring, I can see your problem.
That’s not us but Jones Co is the 2nd agency I was able to contact. First was Crisp SO.

This is us. Here. Site 4 is the main site, not sure why they’re backwards on the regsitrqtion
IMG_2498.png
 

jcefd10

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Absolutely agreed. But he didn’t seem to have any appropriate test equipment handy.

These repeaters need GOOD 6-cavity duplexers if they are at a high level “busy” radio site.
Yeah, I don’t have near what I need. I’m still saving up to get some decent equipment.
We have a 9 can Sinclair JagRF combiner at this site 60571229041__1B4920BC-B256-4BFE-A54D-A57B29DBD0DF_Original.jpeg
 

WB5UOM

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I have a situation like that here now.
The enhanced propogation justakes it worse. anybody using 159.450 as a FB2 transmit within 150 miles can cause you greif and not much you can about it short of changing rx freq.
 

prcguy

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Absolutely agreed. But he didn’t seem to have any appropriate test equipment handy.

These repeaters need GOOD 6-cavity duplexers if they are at a high level “busy” radio site.
With 5 repeaters at the same site it might be better to use a master receive antenna with window filter and preamp then transmitter combiners to feed the other antenna. Total cost will probably be less than using duplexers with separate antennas and performance can be very good.
 
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