Dear Readers,
I have a similar setup to that of SP5EWY, but minus the extra 30mx piece of
wire. The tower is 16mx high with a A3WS and a 204BA on top (plus a 146mhz
collinear vertical).
I run three 1/4 slopers off the tower from the 15mx mark in three
directions. The slopers can be tuned for 80mx (natural length) or have
inductance and extra wire at around the 1/3 length mark from the end added
for 160mx, with good SWR results.
I also shunt feed the tower with an omega match and usually leave the
configuration as: shunt feed on 160mx and slopers on 80mx.
I HAVE ALWAYS FOUND THAT THE SECRET TO SUCCESS IS AS FOLLOWS:
(1) Each unused sloper is left floating from the tower by relays - I have
tried grounding the unused slopers but find more reliable results when floating
(2) ALL cables etc. come down INSIDE the tower right to ground level - so
what you see on 80mx is one tower with top loading, one sloper off the tower
and two other wires floating. On 160mx you see one tower with top loading,
three slopers floating and a shunt fed, omega matched feed up to the 15mx mark.
NO pieces of rotator cable, odd lengths of coax etc., leaving the tower half
way up the tower and off to the shack. All cables are run in 90mm conduit
underground back to the shack.
There are a few radials in the ground of indiscriminate length to establish
a suitable earth reference point.
The system works well, and more importantly, remains with the same tuning
regardless of weather, wet or dry, windy or calm.
For those having trouble with 1/4 slopers, remember you have several variables:
(1) length (usually slightly longer than 1/4 wavelength)
(2) angle of slope (usually about 45 degrees)
(3) height of attachment (the higher the better up to about 3/16 wavelength)
(4) what area of metal above the feed point (the more the better)
(5) height of end above ground and clear from obstacles (preferably clear
from metal)
(6) minimising the points I have alluded to above.
ONE INTERESTING THING TO DO IF YOU HAVE GENERAL COVERAGE TRANSMIT, IS TO DO
A SWR/FREQUENCY PLOT FROM 1.5 to 20Mhz ON EACH SLOPER. YOU SHOULD BE ABLE
TO SEE RESONANCES FOR 1/4, 3/4, 5/4 WAVELENGTH PLUS OTHER RESONANCES OF THE
COAXIAL CABLE UP THE TOWER TO THE FEED POINT. A GOOD LOOK AT THE SWR PLOT
WILL OFTEN GIVE A CLUE AS TO WHAT IS HAPPENING IN YOUR PARTICULAR SITUATION.
Cheers
Peter VK3QI
>Re: SP5EWY's posting on this reflector about half-slopers.
>
>I'm no expert on them, having only used one on 80m for a year. It was a
>very effective antenna, but it totally messed up my 160m shunt feed for
>the tower it was hung from. For that reason, I took the half-sloper down
>and shunt-fed the tower on 80m. The slight effect this had on 160m was
>easy to correct.
>
>I also shunt-fed my other tower on 80m, and the array is definitely
>superior in performance compared to the 80m half-sloper.
>
>Many think the half-sloper is the radiator, when indeed it is not. The
>main radiating element is the tower from which the sloper is hung, as any
>modeling software will show. Apparently the half-sloper acts something
>like an elevated radial, causing the tower to radiate. The pattern is
>nearly omnidirectional (with low-angle radiation), but favors the
>direction of the sloper by 4 or 5 dB. Perhaps three or four
>half-slopers, equally spaced around the tower and fed in phase (one
>feedline), would circularize the pattern (I'll have to try that one in
>my modeling software).
>
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