Odd shortwave interference or jamming

[radioetc]

Lately I have been observing some unusual interference or possibly jamming on shortwave. Bear in mind, I am an amateur's amateur at this stuff. I know a little but I am no engineer. That said, what I am observing is white noise that is repeating every 46 Khz starting ~2 Mhz through ~20 Mhz. The signal is the strongest in the ~5Mhz through about 9Mhz. No problems with LW or AM up to about 2Mhz or above 20Mhz.

To try and narrow down the pattern, I put my Tecsun PL-880 into LSB with .5K bandwidth and logged the high point of the noise as I scrolled in 1 Khz steps stating at 6739 through 7523 and each high point was exactly 46 Khz apart (though 6924 and 7155 were slight anomalies at 47 khz from the previous high point).

Any ideas of what kinds of devices could cause this? I am assuming this has to be very local. Any ideas of how to track this down?

I've tried putting a stretched out paperclip inserted into a female f to male 1/8th inch audio adapter connected into the antenna port and walking around the house and yard. But there is no real consistent nullable direction that I an determine.

Though there does seem to be increase in signal strength near electrical outlets. And yes, I disconnected power to the entire house and no change. So it sorta seems that the noise might be coming in or radiating from the neutral line. Maybe.

Again, any ideas or thoughts would be much appreciated.

Thanks!

 

[GB46]

I used to run across that kind of interference spaced at regular frequency intervals, and it was caused by TV sets in the area. But that was from older sets, especially the non-digital ones with CRT displays, which radiated heavily. Today's digital TVs cause RFI too, but I don't know about the frequency spacing, as there are no TVs in my home, or in neighbors' homes near enough for me to check it out.

Are there any unused cable outlets in your home? TV signals carried by cable from other apartments or even neighbors' houses can interfere even if you shut your own power off.

 

[krokus]

That sounds like plasma TVs. With the number of people that are staying home, that is rather likely.

 

[VK3RX]

Interference from a solar panel installation? Some inverters cause problems.

You can usually pick those as the source if the level and tone is different between day and night, and during the day when a cloud casts a shadow on the panel.

That sounds like plasma TVs. With the number of people that are staying home, that is rather likely.

We have that here - continuous noise across HF that changes when something on screen significantly changes e.g. change of scene or changing channel.

 

[kruser]

Powerline noise caused by arcing connections or insulators and loose hardware atop the power poles.
Sometimes the noise will stop overnight when the humidity levels rise to high levels and rain storms can also cause the noise to stop depending on how bad the connection is. Some can be bad enough where you can see the arcing by eye at night.
The power companies will usually use handheld ultrasonic receivers with parabolic reflectors to pinpoint the source and dispatch a crew to fix it once interference is reported.
Try walking the powerlines with your portable setup and you can often figure out the source. Vegetation that has grown up onto overhead wires can also cause it.

Most power companies are very proactive about these problems and will send a man out to confirm it is powerline noise and then they will find the source and get it fixed. It can save them money by fixing the issue before something burns open causing outages, fires or other equipment damage that could have been fixed by tightening a simple wiring clamp at a pole junction.

 

[a417]

Some can be bad enough where you can see the arcing by eye at night.

You can frequently hear them sizzle as well.

 

[radioetc]

I posted several days ago about this and wanted to extend thanks for the responses.

After a lot of back and forth with devising methods to trace the soure, I think I found it (generally speaking). But am uncertain what to do about it. Hence this second post for addional feedback and advice.

So I've narrowed down the source to be cable/telephone/power lines that cross over my street about 250 feet from my house. FYI...there a different segment of these lines that service my house in the back yard that are much much closer and there is no noise coming from those.

My method of ultimately discovering this was to borrow the ferrite rod antenna from an old amplified AM antenna gizmo I've had for decades. I connected it into the antenna input of a portable shortwave radio. Voila. I could now null out the signal and walk around outside.

I suspect that the real source of the problem is an Comcast/Xfinity aerial line/trunk amplifier located on a pole right where these lines go over the street. I've walked around the block on either side of this amplifier and the signal strength gets lower as one moves away from this point. Bear in mind, that at one point, I got in the car and was able to receive this interference nearly 1/2 mile away so it is very strong. Right under the line with the whip antenna, the signal strength is 55 to 60 db (per the meter on a Tecsun PL-880)

The one facet with this noise that has remained the same since my original post is that it peaks every 46 Khz across most of the HF bands. But it's character has changed where it is now shutting off every 4 seconds for somewhere between 1/2 second or a little longer. And you can hear a weird sweeping sound when it does this. At the moment, the noise is less strong above 9 or 10 Mhz than it was. But it is still very strong in the 3.5 Mhz through 8 Mhz area.

So my new question is, would a cable system line trunk amplifier do this? By the way, as best I can tell, there is no fiber on the pole so this is not an optical amplifier or optical to coax amplifier (I'm pretty sure). Could somebody have a bad TV set that is back feeding garbage directly into the cable system and leaking out the amplifier or perhaps a nearby tap for customer drops? Do I call Comcast to look at this? File with the FCC?

Any thoughts would be most appreciated.

 

[wtp]

i would just give them a call, and tell them what you have found.
probably not the one that "just answers the phone" ask for a tech.
they do drive around looking for leaks, but who knows now.

 

[radioetc]

Another update. A couple days ago the noise inexplicably completely stopped late morning or early afternoon. However, another new noise is coming from the same area. This noise is across large swaths of spectrum, mainly 5 Mhz - 15 Mhz. But it is not consistant. The 46 Khz spacing of the previous noise is gone. The new noise is very weak unlike the old noise. Now it is maybe 2-4 dbμ above the noise floor so very reasonable. Sometimes there is no difference as it is right in with the noise floor, depending. And easy to null. All in all, a much better shortwave listening experience. I fear this noise will return. If it does, I will call utility companies and see what they say.

 

[wtp]

did it rain in between ?

 

[radioetc]

Well, not really. What I mean is that the day this changed, it was sunny. So I was listening in the early to mid morning and the noise was there. then I listened again late morning, possibly very early afternoon and it was gone. No rain.

Now, since that point, it has rained but the noise was already gone. So tentatively at least, I don't think weather had anything to do with it.

 

[radioetc]

did it rain in between ?

Just wanted to post another update, last night I got over a 1/2 inch of rain and the dreaded 46 Khz spaced interference IS BACK! I was listening to the radio last night with no issues and checked this morning after overnight rain and it's back.

Although the main difference with this iteration is that is is not modulating as much noise and is not pausing. Before, it would shut off either every 11 seconds or every 4 seconds for a 1/2 second and then come back on doing a sweeping sound. Now it's just on. VERY ANNOYING. Time to start calling utilities.

 

[krokus]

Just wanted to post another update, last night I got over a 1/2 inch of rain and the dreaded 46 Khz spaced interference IS BACK! I was listening to the radio last night with no issues and checked this morning after overnight rain and it's back.

Although the main difference with this iteration is that is is not modulating as much noise and is not pausing. Before, it would shut off either every 11 seconds or every 4 seconds for a 1/2 second and then come back on doing a sweeping sound. Now it's just on. VERY ANNOYING. Time to start calling utilities.

That makes me wonder if water has gotten into a power supply.

 

[WB9YBM]

"I am observing is white noise that is repeating every 46 Khz "

Since it repeats at regular intervals it sounds like you're hearing harmonics. Also, since it's happening over such a wide frequency spectrum I'd assume it's a digital (i.e. square wave) signal since such a signal generates more harmonics than a sine wave. Could there be equipment nearby with a microprocessor running with a clock speed of 46 KHz?

 

[radioetc]

That makes me wonder if water has gotten into a power supply.

Perhaps. The million dollar questions are where might such wet power supply be located and could it repeat every 46 Khz?

 

[radioetc]

"I am observing is white noise that is repeating every 46 Khz "

Since it repeats at regular intervals it sounds like you're hearing harmonics. Also, since it's happening over such a wide frequency spectrum I'd assume it's a digital (i.e. square wave) signal since such a signal generates more harmonics than a sine wave. Could there be equipment nearby with a microprocessor running with a clock speed of 46 KHz?

Given what I am slowly learning about this I'd say there has to be. The question then is what kinds of equipment would be clocked at or very near 46 Kh? And what would saturate so much HF spectrum and at the same time have such high field strength? If cable TV aerial trunk line amplifiers that hang on the line at the pole would do this, then I have my suspect. But I am getting the impression that these do not cause this kind of trouble.

 

[WB9YBM]

There are a few different RDF (radio direction finding) techniques out there, the simplest being to remove the antenna from the receiver than walk it around to where the noise is the strongest and there's your noise source.

 

[krokus]

Perhaps. The million dollar questions are where might such wet power supply be located and could it repeat every 46 Khz?

It could be locally supplied, or supplied remotely, but there would be some type of conversion, to power the on-pole amplifier. (There could be an amp breaking into oscillation, too.)