Fairly often for several days at a time I get a very loud pulsing or
pulsating noise anywhere from mid medium wave to upper HF. It seems
to pulse exactly at 85 beats per minute.
It's at its clearest right beside or almost on top of any broadcast
station, the closer I tune to a station, the clearer and stronger the
pulsing becomes. Close to an adjacent broadcast its noise frequency
is approx. one or two kHz per second, (using my ears). Between
broadcast stations it has a much lower sound, the rate of 85 beats per
minute does not vary.
My antenna is outdoors, a very random length of wire about 30ft. high,
the lead-in is coax.
Using a small am radio with whip antenna I can hear the noise by
placing the antenna near the power outlets in my house, or the gas
stove, telephone wiring, ground lead going to my receiver, a large
towel rail in the bathroom, (which is about ten feet from my
neighbours house), and from the metal case of my NRD-525 receiver, it
dosen't matter if the NRD is switched on or not. I can also hear it
from the coax lead-in shield. However, the am radio whip does not
pick up this particular noise if placed on or near the actual
shortwave antenna insulated wire.
Switching the power to my house off at the main circuit breaker and
operating the NRD-525 from a battery makes no difference whatsoever,
nor does removing the ground wire from the receiver. With the power
off I can still hear the noise on the am radio as above.
The best I can say is that it seems stronger on the power line outlets
which are closer to my neighbour's house.
I've made a few recordings of the noise, one very slightly below 10mHz
so it can be compared to the frequency rate of the time signal, also
one made on lower SSB on approx. 9MHz, its somewhat mind numbing on SSB!
I have sent a couple of the recordings to the RFI Noise Website run by
Ken Alexander, VE3HLS, and they should be posted there fairly soon.
In the meantime is it possible to email a sample as an attachment to
the RFI list? If not, and if anyone wants to hear it, I can send off
The gas meter outside my house is bonded to the house wiring ground,
as are water pipes, gas house heater, water heater, etc. The antenna
coax is also grounded to the house ground wiring where it enters the
house. The other end of the coax shield is not attached to ground but
goes to one side of a binocular core antenna matching transformer as
does the coax centre conductor. A five-foot copper pipe sunk in the
back yard goes to one contact on the other side of the transformer,
the antenna wire to the other.
Any and all thoughts and or help would be welcome. Where I live RFI
noise levels can get pretty bad at times, this one beats all of them!
RFI mailing list