[TowerTalk] Re: [Antennas] Dipole

[Larry Crim]

ATanner283@aol.com wrote:
>Hi all.....I am putting together a rotatable dipole for 40  meters. I am gg
>to mount it about 10 feet or so above a HyGain TH-7. What are the thoughts
on
>this??? Should I mount it at 90 deg to the tribander or 0 degrees?? I just
>cant get it much above that. Have Rohn 25 tilt over tower at 60 feet.
Thanks
>for any help..............Al/W8FAX

Al,

You already have a great 40m rotary dipole...your TH-7.  Check the archives,
or NCJ articles about gamma matching your boom for 40m.  Most of these
articles are written by N4KG.  I also believe someone has a web site with
pictures depicting their matching method.

I've used a gamma matched TH-6 boom on 40 for years....I works great.  No
need to go through all the trouble of installing an additional dipole...much
less any interaction problem.


73,
Larry K4AB
-----Original Message-----
From: n7ws@azstarnet.com <n7ws@azstarnet.com>
To: ATanner283@aol.com <ATanner283@aol.com>; antennas@qth.net
<antennas@qth.net>; towertalk@contesting.com <towertalk@contesting.com>
Date: Sunday, October 22, 2000 21:36
Subject: [TowerTalk] Re: [Antennas] Dipole


>At 06:37 PM 10/22/00 EDT, ATanner283@aol.com wrote:
>>Hi all.....I am putting together a rotatable diplole for 40  meters. I am
gg
>>to mount it about 10 feet or so above a HyGain TH-7. What are the thoughts
>on
>>this??? Should I mount it at 90 deg to the tribander or 0 degrees?? I just
>>cant get it much above that. Have Rohn 25 tilt over tower at 60 feet.
Thanks
>>for any help..............Al/W8FAX
>>
>
>
>Al,
>
>A couple of thoughts:
>
>1) Have you tried modeling this?  You can do a reasonable job with the
>Eznec demo available at www.eznec.com.
>
>2) You say "tilt over tower" do you mean fold-over?  If so, have you
>considered the extra moment that the tower will be subjected to during
>raising and lowering.  The moment will be the weight of the element times
>the length of the additional mast length (10 ft?) plus the weight of the
>mast times half of its length.  If in fact you have a Rohn model FK-25 58'
>tower, a (very) old data sheet I have before me shows the "Safe Load at
>Apex, Lbs. as 100.  I don't know what the combined weight of your TH-7 and
>rotator are, but I'd guess you're close to the limit already.
>
>Regards,
>
>Wes  N7WS
>
>
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