[TowerTalk] 80 Fone/CW ant reply de K0FF

[K0FF]

Tom I have the same problem myself and have found no automatic or remote
controlled gimmick to be reliable under full power transmitting. The stub
idea may have some merit, but only at the feedpoint, not the ends. To
dangerous to fool around out there. Look in the ARRL Handbook at the array
of sloping dipoles for 40M, they used a similar technique to lengthen the
undriven elements and make reflectors out of them. Perhaps you can do so,
and still feed the antenna with another cable. I never tried that.
Also I refer you to the April 1989QST article by AI1H entitled _"The Coaxial
Resonator Match and the Broadband Dipole". Franks' article has been
reprinted in the Antenna Compendium Vol. 2, as well as some of the more
recent Antenna Handbooks. His approach produces an inverted V  dipole which
is useable at both ends of the 80M band. This one is on my "A" list of
projects to try.

Further:

My own approach is simplistic. I use a 1/4 sloper, and put a switch at the
bottom end where I can get at it. This way I have an natural antenna that
will exactly hit the 2 spot frequencies that I use there (SSB DX "window",
and low end DX CW area)
At the end of the antenna, most relays will be way over stressed when in the
open position. The voltage at the end of the wire is just too high.
Fortunately my sloper is close to the house and a suitable switch can be
made from a ceramic fuseholder block. I used the 6" variety to bring in the
needed wire length to reach the bottom of the band. The switching element is
a 6" piece of 1/2" copper water pipe. Over the top fits a soda bottle (2
liter, plastic) with the bottom cut out. A small hole in the top allows it
to easily slide up and out of the way when changing the switch, and when in
the down position, it keeps most of the rain and snow off the contacts. This
arrangement is quick, reliable and will handle full power. This is the best
arrangement (weather durable) that I've tried so far, and has worked DXCC in
one season. The SWR is flat at the two frequencies it is set to, and being
naturally resonant, it has a fairly wide bandwidth.
I too am still looking for a novel remote switch that can handle the end
voltage (2-3kV maybe more?).
If a kW at the 50 Ohm point develops 273Vat about 5.5 Amps (V= the square
root of P times R), and the end impedance is say 3300 Ohms, the voltage
there must be on the order of several kV.

Pic at:
http://homepages.dstream.net/K0FF/75-80switch.jpeg

When at home, all my antennas are set up for coax feed. When /MM, I can
vouch
for the effectiveness of an end fed wire (500', long, 100' above sea water).
In the first 2 photo's below the copper tubing IS the antenna, and starts at
the
large insulator on top of the rig, goes thru the bulkhead via a ceramic
insulator, and converts to heay braided wire all the way up the topmast and
then flat,
most of the length of the ship.A large neon bulb is clipped to the tubing to
indicate RF.

P.S. the bearded chap is yours truly.
http://homepages.dstream.net/K0FF/9V1.jpeg
http://homepages.dstream.net/K0FF/HP.jpeg
http://homepages.dstream.net/K0FF/ZB2.jpeg


73 Geo>K0FF

-----Original Message-----
From: Tom K Osborne <w7why@juno.com>
To: towertalk@contesting.com <towertalk@contesting.com>
Date: Sunday, September 10, 2000 10:36 AM
Subject: [TowerTalk] 80 Fone/CW ant


>
>
>Hi All
>
>I have an 80 meter inverted "V" and when going from fone to cw, I have to
>let the end down and add a jumper to lengthen it out.  Is there a way
>(not with a relay) to do that from the shack?  Is is possible to use a
>half wave stub and short it at the end in the shack to do the same thing?
> 73
>Tom W7WHY
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