Topband: QTH too small for Beverage!

Geoff Cottrell
Tue, 17 Jul 2001 15:23:43 +0100

Dear Topbanders

My urban QTH in Oxford, UK is small (rear backyard 20 ft x 80 ft), and is
clearly too small for a 160 m Beverage!  This is a shame as I would like to
be able to hear better the DX that I am hoping to work!  As one might
expect in the modern urban environment, there is quite a bit of QRM from
local PCs, TV sets various home "improvement" (!) electronic devices etc.
The BCS TX ant is too noisy for any kind of sensible weak signal reception.

Therefore I have been experimenting with loop antennas for RX only and, at
present, I have three on test: a standard point-fed pennant with
terminating 910 ohm resistor pointing to South America, and two orthogonal
loops N/S and E/W (15 - 20 m of wire each) squished into whatever
rectangular non-conducting surfaces I can find. For example wooden fencing
panels running down by QTH boundary, 6 ft tall, and the end wall of my
house rear extension.  The loop wire is thin PVC. The 2 loops have no
terminating resistors but all 3 antennas are fed using RG58 50 ohm coax and
16:1 pennant-style transformers.  I can switch between them in the shack
for comparison purposes.

It is too early to give any definite operational results so far but am
collecting data and evolving the RX loop system now.  The only thing I can
say so far is that sigs on the pennant are definitely down compared with
the non-terminated loops, an effect I guess may be related to the presence
of the terminating resistor.  All 3 loops have similar areas.  Also I have
just about convinced myself that the pennant can attenuate sigs arriving
from the back - but cannot quantify this more precisely at present.

I would be very interested to hear from anyone out there who has had
experience of how to cope with this kind of problem; I can't believe that I
am completely alone in dealing with it!

Thanks for any comments in advance

Geoff Cottrell

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