In a message dated 10/17/01 11:58:49 AM Pacific Daylight Time,
w5kp@swbell.net writes:<<
I have a C3XL (33' boom) at 80' on a 45G. It works like absolute gangbusters
by itself (have yet to call anybody more than twice to get a comeback, and
even twice is unusual), but naturally I'm greedy and want more, and would
especially like more Africa in the log. After hunting for weeks, I've about
given up finding another used one just like it to stack at 40' or so (F12
wants over $1300 + shipping to build me a new one - gulp). Have received
dire warnings from several folks about trying to stack my C3XL with a
dissimilar tribander below it (you'll never get the phase right, will never
work, bad idea, etc.) So I need to ask the audience, I guess: What's your
take on a new C3 or C3S or something instead of a C3XL at the 40' level,
using a Stackmatch and a swinging gate? Is this more hassle than it's worth?
Is it a phasing nightmare? I'm very reluctant to give up this great single
antenna just to have two alike on the tower.
73, Jerry W5KP
> With a 60 to 80 ft tower, I would go with two antennas,
> one at 40 ft, the other on top. The bottom antenna could
> be a simple trap dipole or 2L tribander with a bigger antenna
> on top. The top antenna WILL have nulls in the ranges
> supported by the ionosphere on 10 through 20M.
>
>>
The warning that "you won't get the phasing right with a dissimilar beam
below" to me is without foundation. If any phasing problem exists or even
connecting unknown lengths of feedline between 2 similar antennas--there is a
simple solution I've used. Set up a FS measuring set up say 10 WL away and
ground wave ham friends where ever they are. Make up short lengths of
feedline and insert them in series for a 1/2 wavelength. Some additional
length is going to give maximum gain. Remove the short lengths and add one
length equal in length. Or if you are like I am, I'd make up one length with
no joints.
The only other problem is with a different beam to phase with what you have,
you will not get the same balanced free space pattern as with identical
beams. Usually it will have less than the typical 2.9 dB stacking gain when
at the right spacing. But it's worth a try.
You can easily see in Eznec these variations with different beams in stacked
arrays even with correct phasing. I've run 18 different combos. One is to
have the highest gain beam on top and the bottom beam one tuned for best F/B.
It will have the broadest vertical pattern that will fill the higher angle
lobs of the reflection factors for maximum signal strength for 2-5000 miles.
A 2 element beam say 100' high will work very well with a few less dB that
those typicall used at that height. But it's much broader vertical pattern
will also fill all the additional higher angle Reflection Factor secindary
lobes with maximu RF for that height and give max signal at more areas. It
receives max signal from those areas also. A 2 element beam at 100' or
higher is far easier to keep up there also compared to the 5&7 beams. The
rotator and tower needs are far less. A Tri-band Raibeam weighs 36 lbs. 2
element beams do a great job at 100' and higher and are a good investment in
particular for the retiree. An expensive crane isn't needed to intsall it
either. A skilled person on the tower can and have installed one all by
themselves. You sleep beter on windy nights also. Repairs if needed are
very easy to make on the tower.
The last 5 element 20M beam I worked on of K2IEG weighed 175 lbs. I came up
with a way to shift the boom 8' to one side and back to repair a coax
connection on the DE the morning of a contest which he usually won and did
again--the CQ 20M DX Contest. He had a great 90' self supporting tower I'd
use even with a TV antenna on top.
For the bottom beam the 2 element quad, Raibeam or Hex beam (also Moxon 2
element) are ideal at around 40' as N4KG has suggested for universal use.
Phasing them with much higher gain beams on top will produce some interesting
results and I will be testing this. I have a stacked beam switching harness
using 3 -1/4 wave stubs attached to a coax switch that allows one to select
the top or bottom beam or both (with additional bandwidth) that I use for
comparisons.
Dissimilar stacked beams hasn't had much play but has interesting advantages
and affects. This is another example of the Poo Pooer's throwing "Cold RF
Water" on something they didn't do right--or in many cases didn't try. There
is a sickening pattern in every area that the better the new idea or design,
the longer it takes to shoot down the "it won't or can't work anti progress
misinformed often educated beyond their limited intelligence crowd." I think
they should be forced to live in a cave. New ideas are needed for any
technology to advance. Patriotism to ones country has finally returned to
the US for survival. We need a "New Idea Patriotism" in the Technical Fields
without the equivalent disaster to occur. We need another "Spudnick"
(however it's spelled.) K7GCO
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