James Moritz wrote:
Dear Tim, LF Group,
I tried some expeiments with measuring loop antennas at LF and MF a
while back - changing the height above ground from 0 - 10m made
virtually no difference. The only thing that made a lot of difference
to signal levels is if the loop is very close to big metal objects,
but even then the difference is only minor unless the metal thing is
big compared to the loop, and within a loop diameter, say.
I would agree with G3YXM about overloading - if you have an
oscilloscope, it is worth connecting it to the loop output to see if
any huge signals are present. I have used elliptic low pass filters
here to reduce the signal level from the local medium wave broadcast
stations to a reasonable level.
Cheers, Jim Moritz
73 de M0BMU
----- Original Message ----- From: "Trevor Smithers"
<[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Wednesday, June 10, 2009 11:40 AM
Subject: Re: LF: Re Welbrook Loops
I use a 1530 as well, its mounted on a rotator about 2ft above ground
level on a Barenco
socket/spike. Works well 80m down to 500khz but being so close to the
ground its a bit deaf
above 80m as you would expect. My understanding is that for hf it
should me mounted high up but
for lf its better low down near the ground.
A rotator isn't really necessary as the beamwidth is quite broad but
where I do find it useful is
nulling out the local qrm, switch modes etc.
Thanks Jim for the info, I'll get myself a length of Fibreglass pipe and
put it up over the roof, just got it hanging off the gutter at the
moment, can hear loads on NDB's during the day, now to find out when the
500kz activity is on.
I've checked the output on a scope and it looks reasonable
73
Tim
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