Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
Help identifying external interference source to our repeater
|
Hello all. I'm hoping someone can help me track down a new source of noise we're hearing on the input to our local 2m repeater at 147.990MHz.
Here's a couple short videos of what it sounds like while driving around the area listening on the input of the repeater. I used AM mode to enhance the noise a bit, but it can be heard under the signal of our weaker FM users on the repeater. A few of the characteristics:
Some of the theories we have are a local cable TV system leaking, one of the 345KV power lines in the area, an electric fence, lighting/signage etc. That noise sound familiar to anyone? Thanks ? - John, N8CD |
¿ªÔÆÌåÓýWhatever it is, you will be surprised.
You need to do a little more,
especially in the DF area. The good news, compared to a human
jammer, is that is is there all the time.
Can you hear it on a handheld on the
ground at the repeater site? If so, take some readings. (remember
to move sideways 10 feet, take? another reading to identify a
multipath reading.)
Can you hear it from a car mobile? If
so, even the simple X-Y grid driving can narrow it down.
A little social engineering. Is it
24/7, or does it comes at go at certain times?
Could be just about anything. I've DF'd
Micor paging transmitters on UHF that break loose. Never had one
on VHF, so far.
Two hours DF'ing will help.
Oh, you are now required to post back
to this group what you find! ::)
Tom K8TB
On 1/24/2021 12:56 PM, john@...
wrote:
Hello all. I'm hoping someone can help me track down a new source of noise we're hearing on the input to our local 2m repeater at 147.990MHz.
|
|
David McBrayer
¿ªÔÆÌåÓýJohn,? A few questions:? 1) Do you have an attenuator to put between the antenna of the 2nd video and the receiver? ?This would allow you to narrow the directivity of the source. ? 2) Have you explored the area in the direction of maximum noise out to about 5 miles from the observation site in the second video. ?If nothing found, go out to 10 miles. ?A satellite view would not likely have been updated since 01 January.? 3) Have there been any lightning storms or significant wind activity in your area since mid-December?? 4) Do you, or your friends, know any ¡°Fox Hunters¡±? ?Their radio tracking skills are a joy to behold.? 73,? Dave McBrayer ¡ª¡ª¡ª¡ª¡ª On Jan 24, 2021, at 09:56, john@... wrote:
-- Dave McBrayer? N6OJJ Castro Valley, CA |
|
Hi John, I listened to the audio and noticed a few things. Each pulse is fast rise/fast fall, 2 or 3 strengths, random, but in spread clusters. Almost like static discharge. Area of coverage suggests extreme high rf source, or something with a long radiation antenna. I would rule out electric fence, because those discharge controllers pulse at regular intervals. I would then suspect the high voltage power lines. An arc-over flash? would have an excellent antenna. Do you notice any change from dry to rainy day? I would hope in the car with the DF and drive the power line. Also, don't know where you live, but if around power generating windmill turbines, they build up a tremendous amount of static electricity on the blades. This is interesting. Keep us posted. Frank N6CES On Sun, Jan 24, 2021, 10:08 AM K8TB <k8tb@...> wrote:
|
|
Hi John, I noticed you are centering in on the repeater's input.?? I doubt that's the strongest frequency (that would be like winning the reverse lottery).?? Look around elsewhere. ? and probably, you may see stronger signals down lower in frequency. ? The comment you just got about the windmills seem valid. ? They can generate a huge amount of static, and regular intervals depending on the wind speed.?? Anyway, as you dial down the band, you may get further clues with more signal.? Good luck! And as previously stated, please keep us informed! Andy WJ9J On Sun, Jan 24, 2021 at 3:41 PM Frank Perkins <N6CES.r@...> wrote:
|
|
John, On initial listening it sounded like it could be a power line issue causing an arc - but the more I listened you can clearly hear it is data of some type, possibly TDMA data or similar due to the "buzz" in AM Mode, with the regular and often similar signal? Observing this signal on a spectrum analyzer may help you narrow down the source as you are likely seeing an image/mix/harmonic from a data transmitter.? It could be any number of things - from a cell phone or cell site to wifi, smarthome devices, or utility smart metering.? We had a similar issue that went on for weeks a few years back that not only intermittently?caused interference on VHF but also drifted up and down the VHF band including into public safety spectrum.? I successfully located the source of that interference after a few weeks which was the transmitter for a J-Tech paging system - the same as those used in many restaurants - located in the same-day-surgery waiting room of a local hospital.? The transmitter had a defect that was causing it to emit a spur in the VHF band and for some reason that spur would slowly drift up and down in frequency over time.? The transmitter was set for anti-walk-away mode which transmits a data signal at regular intervals - and if someone walks out of range with one of the pagers it sets the pager off, decreasing the chance of someone taking a pager or missing a page.? Hospital security powered down the device which confirmed it was the source and tagged it out of service until it could be replaced/repaired. If possible I would recommend that you observe the signal with a spectrum analyzer as this will likely help you pinpoint the center frequency of the interference source, which is likely a much higher level than what you are observing.? If the noise is broad-band this method will also confirm that.? Keep in mind the selectivity of the receiver you are utilizing in these videos is quite broad and as such the signal may be perceived to be broadband when it may not, in fact, be so.? Your input frequency is also extremely close to the upper band-edge of 2M so the chances of receiving interference from a device in the commercial/public safety range is elevated.? Another useful observation would be if you could capture the audio waveform so it can be visually compared to known modulation types.? This can be done using a service monitor oscilloscope mode or simply recording the audio and using an audio editing application to inspect the waveform. Thanks, Dan Woodie, CETsr KC8ZUM On Sun, Jan 24, 2021 at 12:56 PM <john@...> wrote: Hello all. I'm hoping someone can help me track down a new source of noise we're hearing on the input to our local 2m repeater at 147.990MHz. |
|
It sounds just like a good old power line arc. I doubt it is more than a couple of miles away.?
It could be a tree limb touching the primary. Most likely it'd a defective bell or mushroom insulator. As someone has stated use an attenuator to reduce the signal to a point you can get a good reading in the direction. This is not recommended but a light tap on the pole where the problem is will generally reveal a lot of noise. The power company is responsible for fixing what is called "unintentional radiators " but I have found locating them generally falls on whoever is having the problem.? Also the degree of resolution varies greatly with the power company. Good luck and keep us informed. Wayne? WA5LUY |
|
Wayne, This was my?initial thought?as well but aside from a device drawing significant power in a repetitive pattern as observed I am not sure how this could be the case.? Another possibility, though I doubt it would be that strong, would be it could be wide-band PIM caused by interaction between?a nearby high-power transmitter and one or more metallic objects.? The testing I described should help narrow it down if possible - and yes an in-line attenuator, preferably variable, would be helpful in narrowing down the source whether testing?with?a receiver or a spectrum analyzer. Thanks, Dan Woodie, CETsr KC8ZUM On Sun, Jan 24, 2021 at 7:01 PM wa5luy <wa5luy@...> wrote: It sounds just like a good old power line arc. I doubt it is more than a couple of miles away.? |
|
Tree limb touching a power line, or a failed insulator on the power line, is a likely culprit here. ?After listening to the YouTube videos, that sounds like a high voltage arc erupting somewhere close. ?It could be other sources as well but I'd start with the power line arcing first. ?I've had issues with that off and on for years here at my home QTH.
|
|
One idea.... look at your 3rd harmonic on 443.970.?? A local T-hunter taught me that trick.?? Around here the ham radio transmitter hunters use 146.565 MHz, and in addition to that you will find the 3rd harmonic 439.695 programmed into their T-hunt radios...? A signal that is so strong on 2m that it overloads your t-hunt receiver (even with 70db of attenuation in line - it leaks right through the case) will be searchable on the 439mhz channel... from a foot away you still have directivity on your beam and you can walk right up to the 2m transmitter. As others have said please let us know what you find. ? |
|
I had a similar noise on VHF. You could hear it in various places. It ended up being a commercial wireless internet providers new site. It provided about 6 to 8 db of site noise from 138 to 158 mhz. Company failed before we could bring in the FCC.
On Monday, January 25, 2021, 5:02:42 PM EST, M M <wa6ilq@...> wrote:
One idea.... look at your 3rd harmonic on 443.970.?? A local T-hunter taught me that trick.?? Around here the ham radio transmitter hunters use 146.565 MHz, and in addition to that you will find the 3rd harmonic 439.695 programmed into their T-hunt radios...? A signal that is so strong on 2m that it overloads your t-hunt receiver (even with 70db of attenuation in line - it leaks right through the case) will be searchable on the 439mhz channel... from a foot away you still have directivity on your beam and you can walk right up to the 2m transmitter. As others have said please let us know what you find. ? |
wa5luy
to navigate to use esc to dismiss