[TowerTalk] [Bulk] Rehash of 80 CW/SSB Switchable Dipole/Vee

[Grant Saviers]

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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