Low band chasing and interference in the shack

On the Bands
1

Dear RFI Expert:

The background noise levels in my shack on the lower HF bands are pretty bad (e.g. S9+ on 160m and 80m). I’ve listened on several rigs and it’s the same, a general white noise across that part of the spectrum and worse during the day. Effectively, it rules out daytime chasing on 80m for me except for the strongest of activator signals.

So, I had assumed it was general atmospheric noise caused by D-layer absorption, lightening strikes and other natural sources. I haven’t done 80m portable for several years [I’ve even cannibalized my homemade 80m dipole to make a ‘high’ bands linked dipole] but Mark @M0NOM informs me that he gets little or no noise on 80m when portable in the countryside. So, maybe it’s not all atmospheric noise.

I don’t think it’s coming via the mains electricity cable to the shack [a small outbuilding a few metres from the house] as the noise is about the same if I use a LiPo for the receiver [and switch all mains appliances off including lights]. I haven’t yet tried moving the rig and antenna feeder out into the garden and away from any mains cables.

There are mains (3-phase?) electricity cables running up the street on telegraph poles but they are 15m from the shack [and much further from most of the antenna wire] and about 8m up which I thought was too far away to be a problem.

Could my choice of antenna be a factor?: a horizontal long wire, inverted-L configuration (22m horizontal at 8m average height, 4m slope to ground and 9:1 UnUn, short earth wire to earth stake, 10m coax to radio/ATU).

So, any ideas where the noise could be coming from?

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No noise here on 80 or 160 during the day. I get the static crushes from thunderstorms on the continent or out in the Atlantic and beyond at night.
Turn of your entire electricity at the mains board(means really anything in your house is turned off) and run one transceiver on a battery. This may might give you an idea were the noise is coming from.

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ADSL, VDSL, Computers, Game Consoles, Powerline networks, WallWart PSUs, LED lights, Solar panel inverters, car chargers.

Start at the beginning, switch off mains to your house and listen on battery powered receiver. Does the noise reduce? Power on house, and search for noise source with portable rx and small search antenna. Find which local sources are worst, fix them first (replace, or choke leads). Lather, rinse, repeat.

4

Agree with others regarding approach. I believe we live very close to each other and I have low noise levels in the day, and see an increase at night on 160/80. However, I have spent a fair amount of time doing everything I can to reduce RFI on the LF bands.

Switch off mains to your house, turn on breakers one by one. However, common-mode noise on the coax is something I observe when I use an antenna similar to that which you describe. I would suggest a battery and radio at the feed point to check it isn’t coax related.

VDSL affects me worst on 30m. It adds about 7 dB of noise. I don’t suffer too badly on the LF bands. The telephone cables run parallel to my doublet about 25 m away. Bear this in mind for your 15m distance assumption for electricity cables.

A small coaxial (directional) loop antenna connected to a portable radio will help to track down the noise. SDR helps a lot to “visualise” changes in noise, but wandering round with an SDR/laptop is a pain.

I record everything in a notebook when hunting RFI. I regularly check and record noise levels on each band. Finding a source of noise requires a very methodical approach, persistence and sometimes a bit of luck.

73 Matthew M5EVT.

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I’m sorry to say that even if you eliminate all noise sources in your own home by following Andy’s suggestion, you will still get it from your neighbours. Add to Andy’s list things like growlights, fishtank accessories, some flatscreen TV’s, defective thermostats and even freezer motors, and bear in mind that the noise from a faulty insulator on those overhead cables that you mention can radiate for tens of metres and will travel along the cables for hundreds of metres while being radiated. Once you have eliminated your own house as a problem you could take out a small portable radio (the FT817/818 is ideal) and hunt around your neighbourhood. The sad truth is that you may never eliminate all sources, so you may have to think in terms of mitigating the problem in other ways. The antenna may not be helping, much household noise is vertically polarised so the vertical part of the inverted-L may be picking up more than the horizontal part. Reversing its architecture so that the vertical part is as far from the house as possible may help (it did with me). Failing that you could try a small(ish) magnetic loop, which is supposed to be less prone to such noise and its directional properties may help to notch out the worst sources. Finally, you could try eliminating noise by buying or making a phasing unit such as the MFJ-1026 (see MFJ-1026 Noise & Interference Canceler for a successful application.) It will only work on one noise source at a time so it may only reduce the noise rather than eliminating it completely. Then there is the draconian solution of using a remote web SDR…

No doubt I have missed things out but I’m sure that the brain’s trust here will add to the above.

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Then you point out the issue with your neighbours and start offering to buy them new LED lamps etc.

I had an issue many years back with a neighbour. When he hit the turbo button on his PC it wiped out 2m SSB when I beamed his way which was where all the weak EU DX was normally heard.

Did some digging with him with my handy in his shack. He was astounded when the noise came when he pushed the turbo button. No way he would use his PC on slow mode but we removed the LED flexi cable to motherboard and all the noise vanished. He did some tests to ensure it was in turbo mode even if light was off and was happy. I also gave him a 6 pack of beer for being cooperative as a thank you. You can get neighbours to be helpful if it doesn’t impinge on their wallet.

2 Likes
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Sorry - long post! Low noise floor here - Rural plus Full Fibre Broadband so now the noise in the shack is about the same as on a hill - in an IC7300 it is now reading S3 on 80m with a preamp in…

However this has not been easy to achieve. The antenna is (now) a repaired doublet - 200ft long which has significantly lower noise than the inverted L it replaced.

I have spent three weeks with a broken doublet - the end of the openwire feed failed which left the antenna unbalanced and the noise level went to S9 without the preamp.

As I was stuck in the house - self isolating I did a few investigations and tried to deal with the culprits. These seemed to be :- The Cat 5 cables connecting my WAP’s ( I have three) and their horrible switched mode power supplies now managed with about 20 turns round a type 31 ferrite. (x3) This then linked to the computer - connected to the rig - so the cat 5 connecting the computer with the router is no more and replaced by wifi.
The Cat 5 cables (put in place during building work and now behind plasterboard) seemed to be acting like an antenna for noise which was then routed through the computer which is connected to the rig. Cat 6 may be a better choice now for cabling.

The worst culprit was the openreach power supply for the fibre modem - again an even chunkier type 31 cured it - or at least got the level down!

I have also implemented mains filtering in the shack (RSGB Convention lecture 2015 - Clean up your shack - YouTube) and there are a variety of torroids around almost anything in the shack that is connected.

USB leads running from the computer are now heavily wrapped around type 31’s too. It seems the chunkier the ferrite the more effective it is at removing LF noise.

I have three teenage children with a huge number of devices - so managing to keep the noise level down when they get something new to plug in is a pain.

We also have LED lighting - and some of the “bulbs” are better than others - I threw one batch away because of the noise.

I ought to say that removing the computers is not an option - they are needed for work!

It seemed that so many things were causing RFI when I started investigating it was difficult to deal with as nothing seemed to work - but in effect they all had an impact and watching the waterfall on the IC7300 I can now see signals not just noise.

Finally I also have a 40m loop - again it seems to perform well-ish with low noise. That is fed through a balun - and the coax running to the house is again wrapped around type 31 to try and stop rfi entering at that point.

I hope the management doesn’t read this because I would expect that I have probably spent well over £200 on ferrites over the last couple of years, and providing *I can keep the doublet working in the trees it works!

This might also be useful Selecting The Right Toroid & Ferrite to suppress EMI and RFI (1:1 Choke) - YouTube

Good Luck

Paul

2 Likes
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Thanks for your suggestions.

Sadly, powering off the house mains electricity made no difference.

I tried it with a KX2 and a FT817 both on battery power. The KX2 noise [with 4kHz bandwidth, pre-amp on] was S7 on 1900kHz and 3700kHz with the house mains AC on and off. The FT817 noise [with ceramic filter] was S9 on same frequencies.

BTW: I don’t read anything into the difference between the rigs. It’s difficult to set them up the same. I’ve always been unhappy about the KX2 S-meter. It reads low IMHO on all bands unless you have the pre-amp on, which, for 160m to 40m is not needed.

For comparison, my shack rig, a FT857 on a [non-switching] PSU is S9+15 on 1900kHz and S9 on 3700kHz. I don’t have the means to run it from a battery. So that probably needs investigating.

Next, to see if the proximity of the shack outbuilding is a factor I’ll take the rig & coax feeder out of the shack and into the garden to see if that makes any difference, including away from the neighbour’s house closest to the shack.

Then I’ll try swapping the coax feeder with the one from my Chameleon MPAS LIte which has a choke at one end.

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Good idea. Will try that before trying different feeders.

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I hope this isn’t the problem - but it might help with an answer Power Line Noise On Your Ham Radio? How To Find AND Get it Fixed - YouTube - Power Line Noise!

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…on watching it more closely is one of your neighbours growing a lucrative crop in the attic???

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The telephone cables are on the same telegraph poles in the street as the previously-mentioned 3-phase AC mains, strung about 2m lower. However, my 30m band noise is much lower [same for 20-10m]. 6m is awful - a cyclic clicking noise repeating every 4s or so [but then my horizontal long wire is probably very inefficient for 6m].

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VDSL has a 4s training interval ISTR.

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That backs up my theory. A few months ago I drove round the countryside with my FT817 on the passenger seat hooked to my 50/144/432 tri-band whip on the car roof listening to a quiet 6m SSB frequency [as one does on a Saturday night].

In the countryside the frequency was quiet but in the villages (or even a row of houses / overhead cables) I heard the most weird and wonderful noises. Parking right next to the fibre-to-the-cabinet green boxes by our village hall was yet another weird-sounding QRM. The correlation between human habitation or not was very clear.

1 Like
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K9YC has written some excellent papers on reducing RFI. Here are two:

http://audiosystemsgroup.com/KillingReceiveNoise.pdf
http://k9yc.com/RFI-Ham.pdf

List of all his publications: Audio Systems Group, Inc. Publications

This page has some great stories about tracking down RFI sources: EMI - RFI page

wunder

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I just tried connecting the KX2 to the 9:1 UnUn with a short patch cable. There was no improvement to the noise level on 160m and 80m, so I rule out a common-mode coax feeder problem.

I’m increasingly suspicious that the proximity of the inverted-L antenna to the roadside overhead mains and telephone cables might be the source of the EMI.

I’ll try Brian’s suggestion and temporarily connect a vertical extension to the far end of the antenna which is supported by nylon cord from a mature tree and well away from the road and other houses. I’ll move the 9:1 UnUn to that end and try the KX2 directly connected there.

Question is: do I need to remove the existing sloper part of the antenna at the house / shack end to be a fair test?

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S-meter absolute mode is available in the K3, but listed as not implemented yet in the KX2 and KX3. Still waiting for that myself.

wunder

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Is there any way of having a balanced antenna that does not load against the ground?

Paul

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… my 40m loop works well on recieve on 80m… but rubbish at TX…

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I’ve had the KX2 two years now. I’m very happy with it otherwise [okay, not the loudspeaker]. After the first few months of usage I assumed the S-meter insensitivity was a fault with my unit and returned it under warranty to the UK dealer. They tested it and said there was nothing wrong. I suspect their standard test doesn’t cover design flaws.