Hi,
I moved to a new QTH in November (Cupertino, CA - CM87xh) and have been
plaqued
by intermittent noise problems on the HF bands.
I could use some help in IDing the source or type of noise. Or, perhaps
some suggestions
on how to track it down.
The noise has the characteristic AC hum when an AM demodulator is used, and
the motor
boat sound when an SSB dem is used. It clearly shows up as harmonic
carriers. The carriers
appear to be about 10kHz wide.
I've tracked it as low as 1.8Mhz. The harmonics are every 200kHz (pretty
precisely). Every
other harmonic is one to two S units stronger. The signal strength
dimenishes with increasing
frequency. It extends we'll into the 20M band. I'm sure it's present all
the way to 10M, perhaps
even 6M - it's just the signal level has fallen off enough shorter than 20M,
that I can't detect
it quite as well.
Around 5.317.700 (Mhz), another carrier of the same kind can be heard. This
carrier also
repeats every 200kHz. Eventually, in the 20M band, a carrier is present
about
every 30 to 33 kHz.
Between the carriers, the band is very normal - as it gets these days.
The carriers aren't detectable at 2M, 316Mhz, or 70cm.
I had a severe case of power line sparking noise at my previous location -
this doesn't sound at
all like that. I have one low voltage line coming down the street, and one
high voltage line along the
back of the yard.
It's definitely intermittent - I can't discern any pattern to when it's on
or off - this may be the result
of my sampling frequency though. I have checked during wet and dry WX,
daylight, and deep
of night - no correlation. When present, it's on for several hours and
days. I've also gone several
days without in being present. It does start suddenly, like a switch is
thrown - I've been operating
a contest, and it will appear suddenly.
I'm pretty sure the source is not in my house. I've disconnected the
antenna, and the noise
disappears.
Any help would be appreciated.
de -KR- N6RCE
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