In it, the author explained how he had replaced a cheap VGA connector cable with a heavy-cored, multi-screened version that, he claimed, eliminated his RFI issues. All three signal cables, and then the whole cable assembly, were screened.
As earlier reported, I bought a new LG monitor recently, only to find I couldn't use it due to very high levels of broadband RFI.
After trying a lot of the usual solutions - ferrites, chassis grounding, etc - I could only reduce the RFI by a very modest amount, and certainly not to levels that were remotely acceptable in this quiet rural radio situation.
I thought I'd have a go at the VGA cable solution. Having forked-out £25 for a new unit from RS Components, I found it made absolutely no difference whatsoever over a cheap cable.
Somewhat belatedly, I then had the idea of coiling up the VGA cable to form an air-cored choke. This instantly led to a huge drop in RFI, to the extent that all bands were clear of it, except for now very low RFI on a few spot freqeuencies on 12m. I later found 6m was still very badly affected, looking like a loud Russian woodpecker signal across the entire band!
The choke I made was about 5 inches in diameter (I also tried a smaller sized choke, but it wasn't effective), and the RFI began to fall quickly on about the fourth turn, and quite a lot again on the final, fifth turn that I could manage with a thick 3m cable. It's probably a case of diminishing returns, but more windings will probably deal with the residual RFI. Consequently, I've ordered a 10m VGA cable of the cheapest variety, to yield a much larger number of turns. None of the standard split ferrites I have made a jot of difference in any number of installation configurations, and no matter how many I added!
What was interesting to note with this choke was the way in which the RFI changed with slight changes to the physical arrangement of the choke. Holding the choke together with cable ties was OK-ish, but because the windings can't be held neatly in sequence, but tend to run over one another, the choking effect is less than if it is wound around some larger diameter PVC drainage tube. There is, of course, a lesson there for those of us who don't make our antenna chokes very neatly, where the lowered efficiency of the choke isn't so readily apparent!
I did also find that the RFI could be reduced further by winding the DC supply cable many (8-10) times around a large ferrite near the monitor's input socket. I don't think there is any problem from the power supply, but that the choke is stopping RFI that's made it down the VGA cable and into the monitor from travelling down the additional 'antenna' of the power cable. It's probably still worth keeping in place, but the main problem is that VGA cable.
UPDATE (and final word on this!)
The 10m VGA cable duly arrived, and a roughly 22-turn air wound choke made from it, wrapped around a 4.5 inch OD drainage pipe. As expected, this did reduce the RFI considerably.
The RFI initially seemed to vanish entirely, including on 6m, where it was absolutely horrendous, when I connected the choke at the monitor end; previously, the choke was near the computer. A very short lead to the choke prevents any radiating. The image below shows the simple arrangement (ignore the yellow spade connector and wire, it is a redundant test wire. Later, I added a couple of snap-on ferrites between monitor and choke, though they probably achieve very little.
After a day of testing, I did, sadly, find RFI traces on 12m and 6m, which remain too high for my liking, even with a less noisy HP monitor that I have. The RFI, for example, sat on the OY6BEC 6m beacon frequency, which I love to listen out for during aurora events.
So, in the end, whilst I seem to have a very bad monitor for RFI, and did reduce it dramatically, the screen has been removed and won't be coming back into service!
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