LF: Noise cancelling by using optic transmission of RX signals

["James Moritz" <james.moritz@btopenworld.com>]

Dear Andy, Roelof, LF Group,

PA0RDT wrote:
> > Have you tried to mount it on a four metre high non metallic pole?
> > It probably is still inside the noise field of the building, which drops
> > off within a few metres.
G4JNT wrote:
> That wouldn't make any difference.  The mount to the metal frame was
> non contact, and the outer of the coax forming the counterpoise will
> always be the interference injection point as teh rubbish is being
> picke dup on th ecoax outer as it feeds its way thuorgh the ducting to
> the outside world.
Putting the active whip on a mast might not reduce the noise level, if this 
was mainly due to the noise voltage induced on the coax feeder.  But 
increasing the height of the whip above the local ground plane should 
increase the signal voltage induced on the whip, so the SNR should still 
improve.
I think the role of the ground with active whips is often neglected - the 
output of the whip preamp is the voltage differential between the whip 
element and the circuit ground, so the ground connection is just as much 
part of the antenna as the whip element itself is. Clearly, an electrically 
quiet ground is needed for the active whip, whether this is provided by the 
coax feeder or a seperate local ground connection.
Cheers, Jim Moritz
73 de M0BMU