K1TTT wrote:
On Sep 6, 11:41 pm, Art Unwin wrote:
On Sep 6, 2:00 pm, Roy Lewallen wrote:

On 9/6/2010 8:59 AM, K1TTT wrote:
magnetic coupling to the stream seems kind of odd, but it appears to
work for him. i wonder what happens if you go qro? i would expect
some heating of the water and maybe even some ionization or corona
that might cause instability in the stream. i would also guess the
tuning would be difficult in high winds.
Wind would seem to be a weak point. The top of the conductive stream
would dissipate at different heights depending on the wind velocity, so
a gusty wind would be constantly altering the effective antenna length.
Roy Lewallen, W7EL
Part of the speal given talked about the scarecity of real estate for
the many antennas on ships! Why don't they use non frequency dependent
antennas so antennas can be shared, especially when in combat? And
what do submarines use for antennas
when in the stealth mode?

i would tell you, but then i would have to kill you!

Naahhh.. everyone knows they drag an insulated wire, which is why NEC
was updated some years ago to handle insulated wires in a conductive medium.

Now.. when their periscope is up, indeed, there's a lot of special stuff
that goes into shared apertures. Look to the work of Jaumann in WWII..

And with sharing apertures.. it's not so much non-frequency dependent
radiators that is the problem, it's isolation between the Tx and Rx.
Multimegawatt pulses from your radar tend to raise cain with your
sensitive receiver, even if your diplexer does have 100dB isolation.

Finally, it is challenging to make something that can efficiently
radiate at a frequency while not reflecting that same frequency (i.e.
re-radiating). Brings a whole new meaning to "match at the feedpoint"
when your RCS has to be a tiny, tiny fraction of the physical size.
(for reference, the RCS of a resonant dipole with shorted feed is about
0.2 lambda^2)