In message 49f7fe24.959375234@localhost, Don Pearce
writes
On Mon, 27 Apr 2009 18:42:15 GMT, "Brian Gaff"
wrote:

That was what I meant, its audible on medium wave, but the direction nulling
only seems to locate it in our block not much else. I've had all my stuff
out, and the neighbour one way seems clear, but its just like you might
hear from an AC arc, but in a short say up to ten seconds burst, then thirty
seconds of nothing, then its back again, and its very loud on medium, even
worse on long wave and detectable on the fm band as well.
Brian

Don't suppose you could record it and post it somewhere? Ten seconds
is a long time for a switch to be arcing - could it perhaps be a bad
DC motor brush?

10 seconds is typical of interference from an oil central heating
boiler.

In my first boiler, the ignitor was a hot wire coil, but my second and
third (present) boilers have both had sparkplug ignitors. These spark
away merrily until the oil vapour ignites - which usually takes about 10
seconds. Marconi (whose birthday it is today) would be envious of how
far these can radiate.

If the ignition fails, the sparking will continue for up to 30 seconds,
after which the system gives up (and probably locks up until a re-set is
performed).

I found that my previous boiler caused annoying interference to the
amateur 28MHz band (on which I was active at the time), and was also
distinctly audible over a wide range of frequencies. At one of the
annual services, I mentioned it to the service guy. He immediately
fitted a purpose-made 5k resistive suppressor (it seemed that he just
happened to have about his person), and that almost totally eliminated
any sign of the interference. My present boiler is 'liveable -with', and
I haven't had a suppresser fitted (yet).
--
Ian