Thursday, 25 May 2017

RFI - And how your station may be suffering.

Some months ago, I came to understand how my rural, very low noise level is the explanation for why, over all the time I've been operating, I almost always give out a signal report that's better than mine.  This, despite having a very efficient station that uses no ATU on most days, and an almost unique QTH setting on a copper mine.

I'm not the sort to be in some form of competition on signal reports, but I do like to understand how things work.

I also figured out last year that a small 60W testbed solar PV system here produces a reasonable amount of broadband hash (RFI).  To the ear, on most bands from 12m and up, the hash is certainly detectable, but doesn't sound that bad.  The S-meter, meanwhile, doesn't show anything on my FT-450.

Now, 50% of the world's population, and probably a lot more of its ham population, lives in highly urbanised settings.  Most of that population will be suffering RFI to some degree or another.

The effect of even modest RFI is quite remarkable.  Here is a JT65 trace (24MHz) that ran with the solar PV system on (lower half), and then with it turned off (upper half.)  The signal-to-noise ratio clearly collapses catastrophically with the solar PV on, because the signal strength remains unchanged, whilst the noise has increased markedly.

I think you can tell where the PV system was turned off...

So, even if your S-meter shows nothing much, and your ears aren't buzzing with RFI, your station may nevertheless be suffering quite severely from the cumulative effects of urban hash.

What you can do about it is, of course, rather limited.  My approach has always been to invest as little as practicable in a home-based station, and always keep practised in the art of rapid-deployment portable operation.  That way, when your neighbour installs LED lights or a full PV system, you can just shrug your shoulders, not get too upset, and continue working, unaffected, out in the great outdoors. 

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