Dan -
For years I used a setup similar to yours. I had three tribanders, a 402CD,
and 4 wires for 80 and 160 all on a single 90 foot tower. I built a 2X8
remote coax box which was installed on the tower and could switch any of the
eight antennas to either of two feedlines. In the shack I simply had two
rows of eight toggle switches to control the relays. There was a simple
lockout to prevent the same antenna on both feedlines and I could switch
multiple antennas to a single feedline for Upper/Lower/Both style
functionality.
The one wrinkle was that I had a 2x2 relay switch in the shack which could
switch either feedline to either radio/amp pair. This was used in
conjunction with yet another toggle switch next to my two rows of eight.
The purpose of this switch (I called it SWAP) was to automatically switch
feedlines so I could work the multiplier with the good antennas once I found
it. For example, when running on 20 I would listen on 15 or 10 on which
ever of the other antennas I could hear best. Sometimes, it was even a
short beverage. When a new mult was found, all of my key/mic switching was
controlled by the ALT-. function in CT which would also toggle the feedlines
if the SWAP switch was on. This way I could have some hope of actually
working the mult if there was a pileup. In the case of non-overlapping band
(20 and 40) I would have the SWAP off and I would stay on the 402CD for
working the mult.
I don't suggest for a second that this is as effective as separate
monobanders, but I could generally hear as well on at least one other
antenna as I could with a low dipole or vertical and it was much easier to
work multipliers if I could use my best antennas.
Of course all of this can be done manually at time of switching to the
second radio but I do not recommend it. The more things that you have to do
to switch radios the more likely it is that you will forget one and the less
likely that you will actually use the second radio. Alt-. was about my
limit.
On a slightly related subject, if you are going to do two radios be sure to
measure the returned RF power on for every combination of transmit and
receive antennas. A 402CD will return serious power when a TH7 10 feet
below is transmitting on 15.
Hope this helps
73, Tom W2SC
-----Original Message-----
From: Dan Levin [SMTP:djl@andlev.com]
Sent: Wednesday, April 07, 1999 1:18 AM
To: cq-contest@contesting.com; tower talk
Subject: [CQ-Contest] Second radio tri-band antenna options?
Ok - so the goal here is to increase my competiveness for medium
duty
contest
use. Primarily in domestic contests like Sweepstakes and the CQP.
I am
near S.F. in 6-land.
My "main" antenna system will be stacked 4 element tri-banders at
75' and
50'. I will have a rotatable dipole for 40/80 at 85' on the same
tower. I
want to add some kind of tri-band capable antenna for my second
radio to
use.
Space is at a premium, this is a suburban 1/4 acre lot.
The easiest thing for me to do is to put up some kind of vertical.
Since I
am worried about the front end of my second radio given that I don't
have
lots of room (or money, for filters), a vertical seems like it would
give me
the best receiver protection for the least effort. The base
would be about 15' up, the top can be maybe 45' up. The vertical
would be
about 50' away from the tower if it is a dipole, probably 40' away
if it
requires radials. The vertical will be to the south-west of the
tower, a
direction that I pretty much never point the beams in. The U.S. is
east-north- east from here (about 70 degrees).
Seems like the obvious options are a tri-band (10,15,20 meter)
vertical fan
dipole (not too much fan) or a tri-band 1/4 wave vertical with 3 or
4
elevated
resonant radials.
My gut and the computer both favour the vertical dipole, even if the
20
meter
radiator has to have its ends bent a bit (if I can't get 30' of
vertical
space
in total).
Would anyone like to comment, or suggest an alternative that I
haven't
considered?
Would anyone like to hazard a guess about the behaviour of my second
radio's
receiver, when I am running full power into the stack of beams? Is
50' of
separation and vertical polarization going to be enough, or do I
need some
kind of filter to protect the front end?
Thanks for your thoughts,
***dan
Dan Levin, N6BZA
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