[BBC-Micro] Suitable capacitor replacements

Philip Pemberton philpem at philpem.me.uk
Tue Oct 5 16:48:20 BST 2010


On Tue, 2010-10-05 at 16:31 +0200, Rick Murray wrote:
> Any idea what sort of thing could cause this sort of behaviour down a 
> half-kilometre (to nearest neighbour) or further three-phase line? It 
> totally kills mom's Radio4 (pretty much all of the LW/MW/SW bands) and 
> it also kills the internet due to induced noise in the long phone line.

That is NASTY. Must be well above the noise floor to do that to R4.

It's not AC noise (that would be -- as you said -- a 50Hz hum), probably
not motor noise (that's usually a hiss), which pretty much leaves
digital.

Are there any radio or TV transmitters nearby?
What about streetlights? Dodgy light-level switches have been implicated
for this sort of thing in the past.

If you go outside the house and down the street, do you still get the
noise, or is it just present in the house?


> Radio near meter cupboard? Supposed to be practically silent. WTF?!?!?

I'd try killing power to various parts of the house -- isolate
everything to start with (flip the master switch, Igor!), then bring
things back up one by one. If you still get noise with the master switch
off, either your electrician has done something Very Very Naughty, or
the noise is coming from elsewhere.

Next I'd grab a spectrum analyser and try to get full-band waterfall
scans both with and without the noise to assess the noise-floor level
with and without the interference.

Then I'd grab a car, take the SA with me, bolt an antenna on the roof
and do a bit of triangulation. If you know the relative signal
strengths, you can work backwards and find a rough bearing to the noise
source.

I wonder if there's a noise signal riding on the AC wiring... the wiring
would act as a terrific aerial. That's fairly easy to spot, but you
still need an oscilloscope, preferably one with an FFT (Fourier
transform, i.e. basic spectrum analysis) function... if your lights are
flickering, then I'd suspect the farm substation is "just a bit" iffy...
Perhaps the line techs were eager to get home for tea.

-- 
Phil.
philpem at philpem.me.uk
http://www.philpem.me.uk/




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