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Old 1st Sep 2023, 6:32 pm   #1
Bazz4CQJ
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Default Background noise on 80m

I've just been tuning across 80m for the first time in quite in a long time. I'm using my Wellgood magloop with my old Realistic DX-160 Rx and there were lots of strong signals coming in from Germany late last night.

However, more evident during the daytime, is a lot of background noise that I don't recall hearing in the past, detectable from at least 3-5MHz. Every 5 seconds, it stops for a fraction of a second then comes back. It's there on the longwire too, but disappears when the antenna is unplugged.

Any ideas what it is?

B
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Old 1st Sep 2023, 6:58 pm   #2
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Default Re: Background noise on 80m

Probably one of the data-over-power-lines thingies or a poorly trained broadband modem.

In times past some of them could be made to shift to another frequency by firing a couple of hundred Watts of SSB at them.

Alas I have a burblie around 3610KHz here, which when it drifts high messes up my ability to work on the 3615KHz AM net.

I guess that it's not listening on that frequency because I have not been able to find a combination of power and modulation modes that chase it away.
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Old 1st Sep 2023, 7:30 pm   #3
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Default Re: Background noise on 80m

One reason for trying a magloop was that we have both an overhead power line and an overhead phoneline, so there's lots of noise around.

I'll check my router, but I've had this one for ages and I don't recall this noise being there in the past.

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Old 1st Sep 2023, 9:18 pm   #4
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Default Re: Background noise on 80m

I live well out in the sticks (Anglesey), so not usually bothered by modern QRN, but an occurrence at something like a three week interval, is what sounds like a very strong pulse transmission which obliterates medium wave completely with harmonics clearly audible on 80M. It usually lasts for a day. I would really love to know where it originates.
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Old 1st Sep 2023, 10:16 pm   #5
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Default Re: Background noise on 80m

Any military test ranges out there?

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Old 1st Sep 2023, 10:54 pm   #6
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Default Re: Background noise on 80m

For quite some time, I have noticed a distinct transition to quieter conditions above 3700 kHz (Wellbrook and W3EDP). I read a while ago that some devices (SMTs?) contain a filter with cutoff at this frequency.
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Old 2nd Sep 2023, 1:18 am   #7
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Default Re: Background noise on 80m

G'day.

DF the rotten thing and then add a Javelin missile.
We have the same thing here with heterodynes all over the HF bands.
Many here caused by Solar inverters.
A lot of the rubbish disappears when the sun goes down.

You are not on your own with regard to the irresponsible organizations that do not care about RF interference.
Cheers.
Robert.
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Old 2nd Sep 2023, 3:31 am   #8
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Default Re: Background noise on 80m

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Originally Posted by lesmw0sec View Post
I live well out in the sticks (Anglesey), so not usually bothered by modern QRN, but an occurrence at something like a three week interval, is what sounds like a very strong pulse transmission which obliterates medium wave completely with harmonics clearly audible on 80M. It usually lasts for a day. I would really love to know where it originates.
I remember visiting a nuclear power station on Anglesey and in the car park my car door key ceased to work.
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Old 2nd Sep 2023, 7:19 am   #9
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Default Re: Background noise on 80m

Hi Barrie, It doesn't sound like the dreaded VDSL noise that inflicts 80 metres, as that cuts off sharply at 3.710 MHz and doesn't pulse every 5 seconds. I think it's something fairly local. Could be any of the usual culprits. Use a portable battery operated radio, if you have one, and start by turning the power off in your home to see if it's something there. If not venture out into the street to try and track it down.

Hope you sort it.

Cheers

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Old 2nd Sep 2023, 9:15 am   #10
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Default Re: Background noise on 80m

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Any military test ranges out there?

B
No, but we do have the RAF facility at Valley close by. They use radar consistently for ATC, which is not a problem at all. I can't think what they might use which wipes out MW - also LW where you can tune into various 'nodes' all down the band. Listening to the direct signal, it is not just a regular pulse, but sounds like some twiddling of the pulse amplitude or width too.
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Old 2nd Sep 2023, 11:34 pm   #11
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Default Re: Background noise on 80m

I've pushed the old DX-160 to one side and connected up the IC-718.

The S meter shows S8 noise (and this is on the magloop) and I can hear lots of SSB stations (there's a contest on) but most of them are barely above the noise.

Nothing heard on 3615 yet, but it's late at night, and with this noise level

I've got a Sony SW Aub, I must dig it out!
B
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Old 3rd Sep 2023, 2:41 am   #12
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Default Re: Background noise on 80m

I've been around the house with my Sony ICF 7600, but on the first tour, could not pin down any sources. There's a heck of a lot of noise 40 ft from the house (overheard power cable?).

Unfortunately the 7600 does not have an S meter. I think there are two different sources of interference; the one which switches off briefly every 5 seconds and another continuous one.

I did manage to rule out my router.

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Old 3rd Sep 2023, 7:28 am   #13
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Default Re: Background noise on 80m

It sounds like there is a lot of the interference all around you. To find the source(s) needs a well-screened receiver, a switched attenuator (also well-screened) and a few different loop and probe antennae with coax feeders.

The radio you're using won't be very directional in terms of sensitivity to signals leaking in. Its AGC action will remove your ability to hear changes in signal strength.

Back in the day, Eddystone made some receivers for the post office for finding interference sources. Internally they were not at all special, rather like an EA10 circuit, but the screened case and the attenuator and the S meter were what made it useful.

For direction-finding, it's vsry difficult to make an antenna sharply directional. What you can have is a sharp null. However, nulls aren't so effective when the interference is being radiated in many places - say throughout the house wiring.

If you've got a radar running in your area, the signal strength from it can be very large and you can get self-rectification going on in semiconductor junctions, any metal-metal junction with a bit of corrosion etc, and what you detect on MF/HF be the demodulated result.

The appearance of noise stopping briefly once every five seconds could be a very strong signal appearing once every five seconds and blocking your receiver, stopping you hearing continuous noise from other sources!

If there are strong RF sources around, all sorts of strange things can seem to happen.

David
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Old 3rd Sep 2023, 9:30 am   #14
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Default Re: Background noise on 80m

I also have lots of noise over MW right through to about 20 metres on my Eddystone. One day it all went quiet....completely and I enjoyed a noise-free listening session. Next day it was back.....the reason? My next door neighbour had a power outage and all his security cameras and alarms went over to battery operation while they were away for the day.....
Most of his stuff uses PoE (Power over Ethernet) and also transmits digital up the mains wiring.....! I get on too well with him to complain....!
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Old 3rd Sep 2023, 4:26 pm   #15
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Default Re: Background noise on 80m

Well, I had a new neighbour arrive a while ago and he installed a multi-camera system which is PoE! And it does seem to me the interference is stronger on the side of the house closest to him.

Yes, the ICF 7600 is not well-suited to noise detection, but it's all that I have to hand.
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Old 3rd Sep 2023, 7:01 pm   #16
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Default Re: Background noise on 80m

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Originally Posted by Bazz4CQJ View Post
Well, I had a new neighbour arrive a while ago and he installed a multi-camera system which is PoE! And it does seem to me the interference is stronger on the side of the house closest to him.
We are an end terrace. The only thing between him and me is a breezeblock wall......!
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Old 3rd Sep 2023, 7:06 pm   #17
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Default Re: Background noise on 80m

some PoE stuff can be chased away from a spot frequency by blasting it with a few hundred Watts of a pulsed two tone 'tune up' signal. ..
..
Give it a try.
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Old 3rd Sep 2023, 9:11 pm   #18
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Default Re: Background noise on 80m

Many people suffer from QRM ie. devices, whatever they may be. However I dreaded my house move 6 months back but found nothing to worry about. My noise floor (ambient noise) on 80M is around S7 on a doublet which is marginally better than previous QTH. I really do sympathise for those in urban areas with all the crud they get!
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Old 3rd Sep 2023, 11:17 pm   #19
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Default Re: Background noise on 80m

Did you turn the power off in your house Barrie?

There won't be any AM on 3.615 at 11 at night, although I did have an AM QSO with a Belgian station at 9 at night a couple of summers ago, but that was further up the band.

Cheers

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Old 3rd Sep 2023, 11:57 pm   #20
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Default Re: Background noise on 80m

No, but that's on my to-do list. Don't know if this is relevant, but the village has a sub-station, and I'm no more than 100ft from it. I'll maybe wonder around there with the 7600.

I'm sure the magloop was performing better in the past than it is now; maybe that has deteriorated, though I did check out physically a few months ago.

B
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