Topband: Rx antennas

[Rudy Severns]

Here is a little more anecdotal rx antenna info.

Some years back I stretched out a 950' Beverage, running E-W up a 20
degree slope, using RG6 cable and a transformer at the far end to
switch directions between E and W.  It was run through a dense
replanted fir forest just hung on the lower limbs 6-7' up.  It's not
perfectly straight but meanders a bit on its way.  Despite the lack of
perfection it has a very good FB, petty much in line with what you
would expect from an idealized Beverage.  It think it shows that given
a modicum a care it's hard to go wrong with a Beverage.  The only
thing I have to be careful about it pickup from the transmitting array
while transmitting.  I have a relay to ground during transmit.

A couple of years ago I put up a 3-element in line array
(Ref-driven-Dir) which is also oriented E-W and switches direction by
retuning the outer elements to interchange reflector and director.  I
was fanatical in adjusting the array and was rewarded with a very nice
pattern with 20 dB+ FB.  The pattern is cleaner than the Beverage but
a bit broader in the forward direction.  Over the past couple of years
I have found that for weak signals the main array is almost always as
good or better than the Beverage.  Of course the received signal level
is much higher!

I think the similarity in performance makes the point that given
similar far field patterns, in a rural environment, very dissimilar
antennas can have very similar performance.

Up until last year I also had up a full size 2-element 40 m quad with
a rotator.  I used the quad on 160 m as a rotable receiving loop.
There were times when it was the best of the bunch, not often but
sometimes.

I also have a 160 m dipole, running more or less N-S, up about 15' or
so.  A pure cloud warmer.  There are times, especially at sunset and
sunrise when it beats all for weak signals.

Finally I had up a regular shielded loop made from 7/8 CATV hardline,
supported with a PVC pipe up the middle.  I had it mounted on a TV
rotator which worked fine once I suppressed its noise.  A gauge of how
well done a loop is, is the depth and symmetry of the nulls.  If the
nulls are deep, symmetrical and basically on axis you've probably done
a reasonable job.  As Tom pointed out earlier, the shield is an aid to
balancing not a magic potion.  I found that the loop was never as good
as the Beverage for weak signal reception unless there was a more
local noise or signal that I could null out by rotating the loop.
There was one recurring situation where the loop was a jewel.  During
contests while trying to work weak east coast stations in the presence
of loud west coast stations, the deep nulls were often very useful to
suppress the strong signal enough I could pull the weaker one out from
under.  Rather like catching mice beneath the feet of elephants!

One important difference between the loop and the directive arrays is
that the loop, close to the ground, has a lot of high angle response
the arrays don't have.  That brings in a lot of noise from storms and
other sources not terribly distant.

73, Rudy N6LF