I used or tried to use a 308 foot self supporting base insulated
Blau-Knox in the late 70's and early 80's (Picture on QRZ.com) and
although I could not do A-B tests I found it horrible and that was over
a 2 degree buried 260 foot radial ground system for 970Khz right next
to the ocean. I found better use for it by using it to run a rope up to
the top and hung 1/2 wave slopers down to the sea, and that was much
better for RX reports on 160 from Europe. I really expected better
results but was amazed at the difference over many years of testing. I
would drop the sloper(s) to the ground when trying to use the 308 foot
free standing tower...which the books said would be an optimal low angle
radiator. The slopers and even a full sized corner fed delta loop were
always much better.
Herb, KV4FZ
On 10/24/2012 5:44 PM, Tom W8JI wrote:
Did you --or anyone else you are aware of-- ever A-B test a ~120' tower
against a ~300' tower on 160?
I A-B or A-B-C tested several antennas, including a low dipole, the
high dipole, an element from my four square, a ~318 foot insulated
tower vertical, and I think my tall omni vertical was about 190 feet
at that time.
The tall vertical tower was definitely worse compared to shorter
verticals, and had almost no short skip signal around Georgia. I had
isolation chokes for lights and a base insulator, but that 300+ foot
tower was so poor I never used it as a vertical.
By the way, to show how bad interaction is, I had to detune unused
towers even when they were 300 feet or so apart.
If you recall W8LT and the balloon verticals, they didn't do so well
with that antenna at 5/8th wave. I used WSPD, WOHO, and WXEZ (King
Road 350 ft) towers also, but had no A-B tests.
Anything tall or new received good reports, if I told the other person
it was tall or new. This is a common result, similar to the well-known
G5RV effects. Pick an unpopular antenna like a G5RV and say you are
using it in a test, and even if you do not actually switch antennas
the G5RV will get a weaker report over long averages of tests. You can
see a similar effect with guest operators and a no-change switch
position. They always like the better antenna, even when it is the
same antenna. :-)
To avoid the G5RV effect when making A-B tests, I never said which
antenna was actually A or B. I also would randomly change A or B
around in different tests. Just watching reports without changing
antennas at all is interesting.
73 Tom
_______________________________________________
Topband reflector - topband@contesting.com
_______________________________________________
Topband reflector - topband@contesting.com
|