[UK-CONTEST] G3RIR still off the air

[Roger Parsons]

Neil

The problem with tracking down noise using
low(ish)frequencies is that it tends to be
re-radiated. In this case I suspect that the nice
earthed metal pole is acting as a top fed vertical
radiator.....

Top band DF contesters (there, on-topic :-) have found
over the years that it is next to impossible to get
good bearings anywhere near overhead lines, and
contest organisers have therefore put hidden stations
under power lines wherever possible. The technique is
to get as far away from the lines as you can and still
get a signal - that distance will probably be much
greater on 80m than 20m. Take as many bearings as you
can (using a compass) and plot them on a large scale
map, not forgetting to correct for magnetic
declination. With a lot of luck the bearings will
cross somewhere near the actual noise source.

The next technique is better, but involves buying or
begging a vhf AM receiver (air-band is good), and
using a yagi antenna. The problem is that the signal
is not usually radiated far from the source on vhf, so
you may not be able to hear it. So you have to walk
until you do hear it, when the problem becomes an
advantage. Not so bad to knock on only one door when
you are fairly certain that the noise source lies
within. (Going further up in frequency will narrow the
search down even more, but the noise will be
correspondingly weaker.)

It sounds as though it is probably some form of
switching power supply. But whether or not is related
to BT is moot.

Good luck!

73 Roger
VE3ZI/G3RBP



> > From: "G3RIR" <g3rir at yahoo.com>
> Subject: [UK-CONTEST] G3RIR still off the air
> Date: Tue, 24 Apr 2007 14:21:49 +0100
> To: <uk-contest at contesting.com>
> 
> A short while ago I reported a noise which is
> causing me havoc. I have made
> some progress.
> 
> Firstly I am aware that this is not directly contest
> related but I am
> hopeful that there may be someone out there who can
> help.
> 
> G4BJM suggested making a loop antenna and I have
> built one similar to the
> design in the ARRL handbook. Fraser also mentioned
> trying a very cheap
> shortwave RX from Superdrug but they seem to have
> stopped selling them so I
> bought a Roberts 9962 12 band shortwave RX for £30.
> It works very well and I
> was able to walk towards the signal and track the
> source.
> 
> I have tracked the noise to a metal (yes, metal not
> wooden) telegraph pole
> about 50 metres from my antennas. There are 13
> (thirteen) overhead cables
> radiating from the pole and I can't detect which if
> any of these is
> radiating more rf than the others as the maximum
> signal seems to come from
> the pole.
> 
> The noise is horrendous on 14 MHz and I have now
> discovered on 3.5 MHz as I
> have an 80m DF receiver. The noise is wideband but
> peaks considerably every
> 50 kHz. Looking at the waveform there are spikes
> every 100 Hz. Even at 50m
> distance it is S9 on 20m.
> 
> So where do I go from here? Knocking on 13 doors
> asking them to turn their
> mains off etc. is too daunting. I have been in this
> house for nearly 30
> years so perhaps this will trigger me to move to an
> rf quiet location if one
> exists anymore.
> 
> Neil, G3RIR
> 
> 
>


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