Dick:
I know you are trying to wrap up your recommendations on the half sloper, but
will add my 2c for what it is worth. I had a half sloper off my US Tower 72ft
motorized tower for about 4 years. I worked about 60+ countries with this
antenna and recently took it down in favor of a Inverted L suspended between
two of our plentiful Northwest fir trees. I found the sloper to be a very
noisy antenna, and slightly directional in the direction of the sloper wire,
but fairly omni. Almost all of the stations I worked were with QSB and in and
barely out of the significant noise level that is usually there. I had a lot of
ESP contacts. I live a good distance from the metropolitan area, and feel my
ambient noise levels here to be below average.
The only rub with the Inverted L is the big radial field you have to lay out,
but that part is done. It is a much better antenna than the sloper. As far as I
am concerned, the best approach to 160 is to use either of those antennas for
transmitting as both are good transmit antennas, but you will be much better
off with a separate receive antenna. I have no experience with the K9AY loop
antenna, but understand it is very good. A Beverage antenna would be better in
the E-W direction and reversable using DX Engineering gear. That takes a lot of
real estate, but people I know who have them do very well.
I have been experimenting with a 1/2" hardline coax loop antenna lately and am
pretty impressed with what it does. It makes almost all of the white noise go
away, and leaves you with a weaker received signal, but at a better S/N ratio.
It is 6ft in diamater, and I have it sitting on top of my satellite antenna
array as you do want to rotate it for optimum results. Basically you are aiming
the antenna in the direction that cancels the greatest amount of noise. Check
out the following reference for this kind of antenna design.
www.w8ji.com/magnetic_receiving_loops.htm
The design shown about 2/3 down the page showing a split shield at the top, and
with a variable cap at the bottom is the design I built. I got my hardline coax
from the local cable video supplier as they usually have scrap left over when
they do pole installations. They gave me about 30ft for free. It is much
stiffer than RG8U, and holds its shape pertty well. The cap should be a
variable with a range that includes around 900pf at center range (mica
compression). The same antenna will work on 80M with a capacitance value of
around 300pf. I built it in an easel configuration using schedule 40 PVC. If
you are interested, I can provide additional pictures and reference info to
build it. The important thing is that the coax loop be symmetrical and rigid so
that it retains the circular shape.
It is amazing that this tiny little antenna can provide such good results. I
rarely use anything else for 160M receive. I am now working countries in EU
which was very difficult with the sloper and Inverted L. It does resonate at
1.820 which is where I want it for CW operation. I do not miss the 160M noise.
A friend of mine lives within about a block of a major power substation, and
500KV power distribution towers and he was trying to operate 160M with a very
nicely installed inverted L antenna. It was hopeless. He is now working many
stations on 160M with the coax loop antenna for receive.
John Owens - N7TK
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