I was describing the phasing system for my 3-stack of 2ea
C51XR-Hs and one C31XR-H (in the middle). The phasing
may be coherent but my phrasing was not, hi! I said:
" the center C31XR-H is fed with a line
VF times the difference in horizontal placement of the 20-15-10 feedpoint
in the C31XR-H vs. the equivalent in the 2 C51XR-Hs"
what I should have said is (trying again):
" the center C31XR-H is fed with a line SHORTER THAN THE C51 FEEDS
BY VF times the difference in horizontal placement of the 20-15-10
feedpoint
in the C31XR-H vs. the equivalent in the 2 C51XR-Hs"
In other words, the middle C31XR launches a bit early but the wave should
be essentially aligned with that of the C51XRs, which launch later but are
farther forward. Without looking back, I think it works out to 85% of 9
feet.
73,
Jim, VE1JF
***************N4ZR wrote:
Message text written by Pete Smith
>>Would take a heckuva tower -- I'm not sure even Rohn 45 would be heavy
>>enough, but otherwise I agree.
>>The only issue I can see is that running the C51s and C31s together for a
>>4-high stack could be problematical because of the horizontal offset of
the
>>C31 part of the C51 array -- might somewhat degrade the pattern on 20-10.
>>It'd be interesting to model, though.
>>Doesn't VE1JF have something similar? Jim, you out there?
>>73, Pete N4ZR<<
******************VE1JF wrote:
>Yep, I'm out here, and have 2ea C51XR-Hs and 1ea C31XR-H. Because
of tower problems to be detailed when they're settled and hopefully I am
satisfied with the way they eventually were handled, only the top C51XR-H
is presently up and it will come down in order to mount all three on a new
tower.
The phasing arrangement is as recommended by Jay, WX0B: stacking is
37', phasing by StackMatch, and the center C31XR-H is fed with a line
VF times the difference in horizontal placement of the 20-15-10 feedpoint
in the C31XR-H vs. the equivalent in the 2 C51XR-Hs. The feedpoints are
more or less the same for all 3 bands and I'm told this arrangement will be
close enough. This is not an issue for the two 40M feeds.
As I read the proposal for a 4-stack with 2ea C51XRs and 2ea C31XRs,
I was convinced it would work well but as Steve, K7LXC pointed out, the
spacing is tighter than F12 recommends--mine is the minimum, so I more
or less fill up 112' of tower with a 3-stack. Only modeling and an
analysis
of how much you would get in performance for the extra bucks could say
for sure.
On a slightly separate issue, the 20-10 section of the bottom C51XR-H is
fed through a WX0B splitter so it can be fed either through the Stackmatch
or via a separate feedline (for SO2R, M/S).
The first C51XR-H alone, at 112' over the land and 317' over salt water to
the horizon, is performing very well on all bands 40-10, despite being over
2wl above the salt water even on 40. I'm looking forward to experiencing
the entire array, but it looks like it may be summertime. I'm proud to
have
convinced Tom to build me the first C51XR-H. So far, its elements look
just great even in the midst of shrieking high-gale-force winds. It loads
well (tuning by K7LXC) and seems quite potent in pileups and running.
The VE1JF array design, saga of construction (!) and modeling and practical
results will be covered in a forthcoming CQ Contest article which I will
write
when the returns are in from the outlying precincts (the tower re-project).
This
will include the F12/ComTek 4sqs on 80 and 160. The 80M can be seen on
p. 9-13 of ON4UN's new edition of Low-Band DXing, above the caption "The
Dream QTH of VE1JF".
73,
Jim, VE1JF<
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