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Old October 30th 03, 08:56 AM
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Thank you Richard!

N8KDV: Why?

Goals:
- single antenna setup
- little or no need for tuner, or at least little need of re-tuning
every 3 kHz
- effective broadband response, i.e. low likelyhood of really dead
spots thru the spectrum
- unlike a T2FD, still very usable on MF/LF for listening using an
ultrabroadband double-transformer impedance adaptor (receive-only
types, confirmed usable for QRP)
- compromises accepted for efficiency, radiation pattern

It is really telling that professional setups hardly ever optimize for
narrowband coverage. The cage-discone is a prime example.

If you trawl the web, you find many examples of very rough "vertical
monopoles", and I have seen they fall into 2 main categories:
- multiple vertical masts (usually 2 or 3), with a symmetrical
horizontal crossbar, fed from a broadband transformer, cold end
grounded to ship deck
- cage designs, either cage-discone or just a huge paunchy
ellipsoid-like cage.

Either way, SWR may wag a little, impedance mismatch is roughly dealt
with by transformer, and a big whocares for rad pattern etc etc. This
is what you need for spreadspectrum, ALE, multiplexing etc. Multi-kW
transmitters help. Some of those commercial military designs are
rated for tens of kW continuous. At most, I'll put 5W into this
thing. Maybe.

Richard, your design seems to favor a lot of parallel wires, but the
big improvement in broadbanding seems to be going from 1 to 2-3 wires.
Does the model confirm that? I have no modeling SW - what do you use?

Also, everyone,

- any hints at to whether wire diameter matters? Commercial antennas
have EITHER lots of wires OR thick masts. Is that out of mechanical
or electrical considerations?

- what are the dimensions of typical HF multiwire monopoles in actual
use on ships?

and

- don't u thing a multiwire cage sloper looks ubercool too?? a real
neighbour-pleaser!
 
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