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
--
CQ-Contest on WWW: http://www.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST@contesting.com
>From Dick Green" <dick.green@valley.net Wed Apr 7 08:36:46 1999
From: Dick Green" <dick.green@valley.net (Dick Green)
Subject: [CQ-Contest] Re: [TowerTalk] Second radio tri-band antenna options?
References: <017b01be80be$6cbb2c20$b3288ad0@mediacity.com>
Message-ID: <016901be80c9$6b4ad240$1ca473c6@tpk.net>
> 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.
I use a multiband vertical with my second radio and it works reasonably well
for gathering multipliers. However, I lust for a second tribander, either
rotating or fixed S or NE.
Do yourself a favor and build your antenna switching system to be able to
use any antenna on either radio. You'll be glad you did. In addition to that
capability, I have a special switch that swaps the tribander and vertical
between the two radios.
> 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?
It would certainly be a guess. Separation is probably the biggest factor,
but there are a lot of things that affect how much interference you will
see, including types of antennas, gain, F/B, F/S, typical directions of
operation, the type of radios in service, and the specific band combinations
you expect to use. Basically, you have to build it to find out how bad or
good it's going to be. 50' is not very much separation. Most of my antennas
are 70'-100' apart, and I still get some interaction, although considerably
less than I feared. My minimum separation is about 35', between the vertical
and the 80M vee, and those antennas just can't be used together.
Fortunately, I never use that combination (if one radio is on the vee, the
other would use the tribander, not the vertical.) I get virtually no
interference at low power. The problems are strictly at high power. There
are only a handful of unacceptable band combinations. I built a pair of
automatically switched bandpass stubs that fixed that. In general, I can get
within 1 or 2 KHz of the harmonic -- not bad. Others have used transmit
and/or receive bandpass filters with good success.
My advice is to build the best antenna setup you can afford/fit, try to
separate the antennas as much as possible and worry about the interference
later (and think hard about making that second multiband antenna
directional.)
73, Dick, WC1M
--
CQ-Contest on WWW: http://www.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST@contesting.com
|