...you may ask the neighbours to place a wire antenna close to their
house, picking up strong E fields :-) These signals fed to a JFET source
follower, then use a transformer somewhere in your RX chain and add some
turns on this transformer (0/180 deg switchable) for the compensation
from the noise pick up antenna. For a single strong noise source it
could help. Maybe a mains HV overhead line travelling nearby. With a
small probe close to the noise source it could work just to pick up the
noise and only little of the wanted signal.
The software hum filters perform not so perfectly as it looks because
the sharp notches can lower the performance of a noise blanker... The
method is rarely used so it seems it doesn't work well in most situations.
73, Stefan
Am 13.04.2017 15:43, schrieb g3zjo:
On 13/04/2017 08:27, John Bache G7JMZ wrote:
Blue sky idea:
Hi John
Good thinking.
I think the hum filters used in SpectrumLab specificity the Paul
Nicholson ones work in that manner. A lot of the mains borne
interference is from consumer gadgets with switch mode supplies,
causing bands of QRM right up to 7.5kHz plus, worse at the moment due
to school holidays I suspect.
73 Eddie G3ZJO
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