Grant,
Great solution to broadband our 80M dipoles, thanks for sharing !
I am going to try it on my 80M inverted V.
73,
Bob
K6UJ
On 4/25/16 2:49 PM, Grant Saviers wrote:
I think the simplest broadband 80m dipole is the one W6RNL/W6NL
proposed. Resonate at 3675, then 1/2wl of 50 ohm coax to the
feedpoint, then 1/4wl of 75 ohm coax, then any length of 50 ohm you
like. My EZNEC/autoez otimized design came out 129.2' dipole, 107.3'
RG8X-LL, 44.2' Belden 8281. Less than 1.6:1 3.5 to 3.9 then rising to
2.1 at 4.0. I cut the coax to length with an antenna analyzer, since
the velocity factor can vary quite a bit from nominal spec. This is
being built as a Field Day antenna so the swr voltages on the matching
sections aren't a concern, but for QRO RG11 and RG8 sizes may be
needed, lower loss is better. (although w/o the swr the small coax is
fine for QRO at 80m, so they might be worth a try given the weight &
cost savings)
Modeled better than 2.1:1 swr for the full band, w/o any complications
of jumpers, raising/lowering, switches, caps, inductors, etc. For
pluggable cw vs ssb stubs near the dipole ends, there can be some
mighty voltages and opportunities for corona or arcing with jumpers at
QRO.
http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1993/09/page27/
Fans, bowties, staggered designs, etc. can all be a PITA with the
multiple wires, strings, spacers, etc. but will have lower loss than
the coax resonator match. Some of these are also very sensitive to
height and shape.
EZNEC with AutoEZ driving it are an amazing tools for finding an
optimal design, running hundreds of design trials automatically.
ac6la.com
For a pluggable cw stub addition to a ssb dipole , the suggested
banana plug on the stub is the way to go and a jack on the dipole.
Then there is no high voltage wire waving around in the air. I
drilled Budwig HYE-QUE HQ-2 insulators (small, light & deep ribs) to
fit a 10-32 screw for the wires to the plug and stub and slightly
larger for a cheap Chinese banana jack w/o an insulator on the ssb
end. That worked fine for multi-band tuned radials for an "on the
beach vertical" at 500w.
Grant KZ1W
On 4/25/2016 9:57 AM, CJ Johnson wrote:
Howdy-
I have been working on rebuilding my 80M dipole setup for camping and
the
fall/winter contest season.. My one main question is I know that I
can make
the ends for SSB, tune it where i want (most likely 3800).. then on the
other side of the insulator, add the extra length for CW and tune that
portion (~3550).
I *don't* have a pressing need to have this remotely switchable or other
things as discussed in the archives -- a semi fancy matching setup, etc.
Given that the dipole is temporary in nature, it doesn't pain me to walk
outside and clip on the CW section when I want to.
That brings me to a couple questions maybe someone can help:
1) The dipole is being constructed with materials to handle 1500W
(balun,
wires, etc.) -- Will this extra length of wire for CW arc where I
"clip" it
on to add the extra length at the end of the SSB wire running 1500W?
2) Given that it's "temporary", how would one suggest constructing the
point where I switch from SSB to CW.. Alligator clips? There may be a
potential for exposure to the elements (mostly rain and some snow).
Thanks,
WT2P
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