Hello Topbanders, just wish to tell you about my sloper system, I used some
years ago on 160.
This was installed by me on 160 after hearing of the success of such as system
from Roy, ZL4BO and Dave, VK3EW who both used it on 80.
It is four quarter wave slopers, fed at the top (no radials) as a four square
(NE, SE, SW, NW), each element fed with a quarter wave electrical 50 ohm coax
(I used RG213) and a switching box so that when one element is fed, the other
three are open circuit.
The top braid of each coax connected together, separation of fed points maybe
one metre.
The open circuit coax stubs are intended to load the unused elements as
reflectors (that is one theory, the other is that the quarter wave coax stubs
act as a phasing stub, signals picked up by the unused element travel down the
coax, see an open circuit and reflect back up and radiate in phase with the
driven element. Both explanations are probably saying the same thing, but in a
different way).
In Dave's case he had a tower with his TH6DXX? on top, in Roy's cases I don't
know if he used a tower.
In my case I used my pine tree 30 mtrs high which also supported my 160 dipole,
with open wire feeders.
In the shack I could switch between this system and my dipole to compare (the
dipole was detuned - not resonant when using the slopers, although I could not
detune the slopers when using the dipole, so some interaction this way).
Dave said his is at the 85 fth and was getting about 20 dB front to back on 80.
Being fed at the top give greater bandwidth, easy matching to 50 ohms (by
adjusting the slope of the wire) and lower local noise pick up as the feed
point is greater distance away from noise sources (wire fences and building
wiring).
In my case on 160 I was also getting 15 to 20 dB front to back, but only on low
angle and ground wave local signals. At high angle local skywave signals (100
km distance) or medium angle (200 to 1000km) not so much F/B.
The sloper system also produced many S points gain for long distance DX
compared to the dipole, but only when the band was just opening (long before
sun rise) and when the band had closed (long after sun rise).
Same effect before and after sun set time.
For medium distance DX the dipole was better or during the peak of the opening,
they both seemed to be the same on receive for signal strength (the sloper
system had lower noise due to its front to back) but the sloper seemed to get
out better on my transmit.
There were many times when I could hear stations on the sloper system who were
S7, but could not detect them on the dipole, less than S3 (my noise level on
dipole).
A great test signal at the time was the Loran navigational pulse beacon. Many
times I could copy this signal S7 with the sloper system and could not detect
it with the dipole. I presume the Loran had strong vertical polarization and
was coming in at a very low angle (less than 30 Degrees). I expect my low
horizontal dipole (only 30 mtrs high) has no pick up less than 30 degrees.
Unfortunately (or fortunately) this Loran test signal does not exist anymore.
After a few years of using this great 160 DX antenna, I had to take it down as
the possums or rats did eat through the coax and had always planned to put it
up again.
Now the strange new chapter to this story is that recently I did try to install
a similar antenna using RG58CU, which was hanging free from a tall overhanging
tree branches and held up with big ropes. I put systems up for 160 (29 mts
high) on one tree and 80 (28 mtrs high) and 40 (27 mtrs high) from another tree
(all three from one branch I though would be too heavy for the branch) and I
expected to have some great lowband DXing, even though the front yard is full
of wires and ropes, much to my neighbors puzzlement.
But to my surprise I could not get anything like the previous results.
I cannot figure out what could be the reason, I am still scratching my head.
There were times when my new systems seemed to be behaving like one driven
element and three directors. The best element was the one diagonally opposite
to the direction of the best received signal.
The long run of RG58CU to feed the 160 system (100 mtrs in length should only
result in 1 or 2 dB loss, so still no idea here.
This sloper system certainly works for others and it has worked before for me,
but I can't make it work now.
I have not given up yet and plan to build or buy a four square phasing box like
the Comtek and try and drive the four slopers that way to get the right results.
Any suggestions with my problem would be appreciated.
GL Ron vk3io@iinet.net.au
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