Reducing the noise floor

One of the problems, especially in built-up areas is high local noise. This video is an attempt to make it better.

RX noise

An increasing issue especially in built-up areas is noise on receive. Increasingly, people are using switched mode PSUs with, for example, TVs. Also, there are inverters with solar panels. The result of all this is the noise floor, especially on the lower HF bands is going up and up. 

One solution is to use a separate antenna for receive and transmit. One approach is a low dipole for RX and a vertical on TX as in this video. Vertical antennas can pick up lots of local noise.

Noise issues

At the moment I am fortunate in that I am not plagued by too much HF noise. It is high on 160m, 80m, 60m, 40m and 30m, but I have not had problems with FT8. Others have been less fortunate with a worsening HF, and sometimes VHF, noise floor. As time goes by, this could get worse.  In the end, the only noise-free bands may be 70cm and higher.

One person who cured his problem is G4SWX, who had problems from the neighbour's LEDs on his patio. Many problems are due to substandard parts that don't meet EU regulations. Companies cut corners to save a few pence and get away with it as there seems little OFCOM enforcement. If I am wrong, please accept my apologies.

See https://groups.io/g/RSGB-Workshop/message/4797

Topband Noise

Although I can't speak for you, here in rural Cambridgeshire the noise on 160m is probably at least 20dB worse than 10 years ago. To be honest, noise on the lower HF bands is bad and getting worse. Even on the higher bands it is a real problem for some. In many ways I am quite lucky!

If you are lucky enough to live in a quiet part of the world (do they exist?) you might like this simple 160m antenna I used some years ago. It worked remarkably well.

See https://sites.google.com/site/g3xbmqrp3/antennas/160m_loft_ant

Broadband interference?

If you were thinking of complaining to OFCOM about broadband noise you may want to think again.

See http://www.ispreview.co.uk/index.php/2017/06/ofcom-finds-no-evidence-claims-interference-vdsl-broadband.html

The fact that our HF noise floor is gradually getting worse is of little concern to OFCOM. Only money matters sadly. In the UK the amateur radio service is unimportant.

After the noise: 160m CW QSO

Following my small successes last night battling my local man-made noise sources, this evening I managed nearly a full QSO with GW0IRW on 160m CW when running 5W to my vertical coax to the 10m halo. The noise level is now low enough to sensibly copy stations on 160m, which I've not been able to do for months at night.

I am now monitoring 474.2kHz WSPR hoping to improve on my reports now the local noise floor is much lower. SM6BHZ is already coming in at a respectable -14dB S/N. He is usually pretty strong so it will be interesting to see how many others come through this evening.

Winning the noise battle a step at a time

This evening I've been trying to track down various noise sources that have been making reception on MF and the lower HF bands all but impossible in recent weeks. I'm pleased to report a couple of successes.

My first "trap" was the 12V Netgear AD6612 AC-DC adaptor that feeds my Virgin Media internet superhub. This little terror was producing an S6-8 noise floor on many of the lower ham bands. I tried ferrite chokes in the leads but to no avail. Fortunately I had an old Linksys 12V supply with the same sort of rating and 12V plug. Swapping the PSUs over and, guess what, the lower HF bands were much quieter once again.

At 470-500kHz though I still had an S8 noise floor, so there was another candidate noise generator around. Switching everything off in the house the noise floor dropped, so it was in the house. In the end I tracked this down to a Salus mains powered controller that receives wireless signals from the central heating roomstat. Turning this off and, guess what, 470-500kHz goes much quieter too! This unit is quite close to my antenna wire and must have a noisy SMPSU inside. Luckily we tend not to have the central heating on in the evening so all I have to do is turn off the Salus wall unit controlling the central heating boiler and I can, I think, go back to better reception on the MF bands in the evenings.

In 30 minutes I've reduced the noise floor in my home considerably from LF to at least 10MHz. This goes to prove that with a little bit of detective work we can do a lot to overcome many of the noise issues plaguing us these days. Both the Virgin Media superhub and the Salus unit are new (less than 6 months old) so this also explains why the noise issue was not such a problem last autumn and winter.

If you have a noise problem then I recommend you do some detective work and very good luck.

MF "swish, swish, swish" interference

In recent months I've been suffering from man-made noise on MF which was not there before. I've a constant S8 noise floor now (it was around S1-2 before) and as I tune from 300-500kHz I get a rapid  "swish swish swish" every few hundred Hertz. I think there are frequencies where it is stronger but the new 472-479kHz is BAD, although I still manage WSPR decodes from DK and SM. For CW it would be just about impossible.

Now, I haven't yet tried to systematically work out what this is yet and nor have I tried a small external loop on RX or an E-field probe down the garden.

Before I start to investigate, does anyone have a clear idea what this rapid "swish swish swish" QRM is likely to be? I don't think the source is in my own house and on one side the neighbour's house is currently unoccupied. I have tried the obvious (turning off lights and SMPSUs in my own place) with no success.

Any knowledgeable help would be much appreciated.

Man-made interference at MF and LF is a critical consideration for newcomers. I hope that a new version of the RSGB book "LF-Today" (if one is planned) will give some information on how to search out such sources and some strategies for how they might be mitigated.

Optical receiver noise floor measurements

A PC with some simple free software makes a very useful piece of test gear.

For example, today I wanted to check the noise floor of my optical receiver head between 0-20kHz in total darkness and in daylight and compare this with the noisefloor of the PC with the head turned off. SM6LKM's excellent little software receiver designed to listen to SAQ's transmissions on 17.2kHz was ideal. This tunes from 0-22kHz. Here are the results (see plots) which show noise goes up by about 5dB in the daylight, although noise at 0-2kHz seems to go down in sunlight. By connecting the optical receiver head to the PC I was able to use this little package to see the noise floor changes.  G4JNT thinks the FET is possibly being biassed to a less optimum position, or it is saturating, in daylight. By changing the bias I may be able to get a lower noisefloor and better sensitivity. That I shall try tomorrow.

Diurnal Variation in Dreamer's Band Noise

Over the next 24 hours I am doing a test to measure the change in VLF noise floor between 0-24kHz. DK7FC has let me have a suitable .usr file for Spectrum Lab to allow this to be recorded. You can see the results on the G3XBM VLF grabber which is updating the plot every 15 minutes.

Another source of LF/MF and HF interference

This was posted on the LF reflector: we'll have yet another source of LF/MF and HF interference in the years ahead as more people install such systems. Hugh's post got immediate replies from people who'd suffered bad interference from such systems. beware of photocell panels on neighbours' roofs!

"My neighbour informs me that she is intending to have photovoltaic panels installed on her roof, in a scheme where she gets free electricity (all subsidised by the government of course!)

My concern is the possibility of high levels of interference generated by the kW inverters needed to pump electricity back into the National Grid. I would guess that such invertors probably operate kHz and might be expected to interfere with LF and VLF reception. The wiring to all the panels on the roof might act as a
very good aerial!

It also occurs to me that any lack of RF immunity to my transmissions, in the new installation, might have dramatic consequences - I know from studying electrical engineering at college that connecting a generator to the grid with incorrect phase leads to a big bang!

Has anyone any experience of such installations? Perhaps someone has one nearby and could comment on any EMC effects.

Hugh M0WYE"