Petr Maly wrote:
Hello LowFers.
I have made loop ant for rx and it seems not to work satisfactorily. Size is
1.75m x 1.75m. Everything is done as usual, with grounded middle and
amplifier with 2 x BF245, tuned properly, etc. Output level from the
amplifier is high enough. I can hear Greek RTTY, also galloping horses a
little, but no poor HAM sigs. My LW 40m, that is in average height of about
6 m only, is much better. The only thing I am in doubt is the number of
turns. It has got only 18 turns (I used flat cable that was available at the
moment). Could this be reason for the bad results? What are your
experiencies with loop ant? Can loop ant be as good as "big" Marconi?
73! Petr, OK1FIG
I also had a bad experience trying to use "computer ribbon" for the loop
winding. The loop did not perform as hoped for (did not result in
external QRN being the dominant background noise). I found there is
high capacitance between conductors, which is not good for high Q use
when terminated as as a "multi-turn coil". The PVC insulation may also
be lossy at LF. Whatever, it did not work as a high Q construction
technique for a frame loop receiving antenna.
Regarding the number of turns, that is another matter, as the basic
parameter is the loop aperture. Number of turns is more to do with
internal impedance matching than collecting signal power.
73, Bob ZL2CA
|
