Thanks very much John !
You are right on 15 m boom interaction with 20 if mounted 90 degrees apart.
My 1st plan was to use 3 element 15 and so with short boom on this tower (as
I will have another 15 on other tower anyway). That would probably be OK,
but currently I'm planning to go with 155CA, and then its boom resonance is
probably somewhere around 20 m band and it could be an issue. I forgot it.
OK, so assuming that 40 m LL yagi would not resonate on 15, then actually
best thing to do would be to align all 3 booms same direction and create as
much as possible separation between 15 m yagi on top and other 2 lower
antennas. I do have long chromoly mast already inside tower which after
rotor is installed would stick out about 18 feet, so there is good length
available. I don't intend to use entire length of it due to mechanical
concerns, but still I think it would be possible to get something like 14 ft
separation from 40 and maybe around 8 ft from 20 in middle, this would have
20 and 40 still 6 feet apart from each others.
73 Marko n5zo
-----Original Message-----
From: john@kk9a.com [mailto:john@kk9a.com]
Sent: Wednesday, August 13, 2014 4:18 AM
To: towertalk@contesting.com
Cc: marko.l.myllymaki@gmail.com
Subject: re: [TowerTalk] 204BA boom resonance, problem for 40 or not ?
The 204ba boom will have no effect on the 40m beam if parallel. Regarding
15m, the linear loaded 40m beam is not resonant on 15m so there should not
be problems mounting it 11 feet above and parallel. The only issue for it
would be the 20m beam 3 feet below which would severe interaction.
Turning the 15m beam 90 degrees may cause other issues depending on the boom
length. I model all of my antennas and mount them on the tower so that
interaction is minimized, I suggest that you do the same.
John KK9A
To: <towertalk@contesting.com>
Subject: [TowerTalk] 204BA boom resonance, problem for 40 or not ?
From: Marko L Myllymaki
Date: Tue, 12 Aug 2014 21:57:24 -0700
Hi,
Would anyone have any insight to offer on this or real life experience of
this combination you could share:
I know some of the tribander booms+end elements such as KT36XA with
non-insulated elements can resonate on 40 meters and so messing up with 40 m
yagi if mounted on same mast nearby. There was great article of this in NCJ
while back. KT36XA boom is 32 ft long.
Does anyone have insight if same issue happens with 204BA with its
non-insulated elements and 26 ft long boom, or does its boom+elements
resonace fall outside of 40 m band ? Is there someone who has modeled this
?
If tribander boom+end elements resonance actually does fall on 40 m band,
then is this even problem if booms of 40 m and tribander are aligned, or
would it be problem only if antennas are 90 degrees off each others ? Have
heard various opinions on this and I don't have yet my own experience on
some of these things.
I'm considering what combination I will put on one of the 2 towers. Current
plan is now to have M2 40M3L linear loaded yagi at the bottom of mast, then
maybe around 8 ft above that 204BA and some 15 m yagi another few feet above
20 m. Booms of 40 and 20 would point same direction and 15 at the top would
be 90 degrees off in order to minimize coupling between 40 and 15 m
antennas.
I have 40M3L already in my possession, but I'm trying to decide what to do
with 20 and 15 on that tower. There are other possibilities, but above is
what I'm currently considering.
Need to decide path to proceed fairly soon, and I'm not planning to start
learning modeling SW right now.
I would very much appreciate any insight and experience on this combination.
73 de Marko N5ZO
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