[TowerTalk] TowerTalk Digest, Vol 81, Issue 48

[AB5MM]

Lloyd, what are your thoughts on this?


Today's Topics:

    1. HB 3 ele 40m Beam (David Jordan)
    2. Re: HB 3 ele 40m Beam (Stan Stockton)
    3. Re: HB 3 ele 40m Beam (David  Thompson)
----------------------------------------------------------------------

Message: 1
Date: Mon, 21 Sep 2009 13:22:01 -0400
From: "David Jordan" <wa3gin at comcast.net>
Subject: [TowerTalk] HB 3 ele 40m Beam
To: <towertalk at contesting.com>
Message-ID: <008301ca3ae0$082fb4f0$5a688f45 at DTSFBXZ441>
Content-Type: text/plain;	charset="us-ascii"

Hi Folks,

Finishing up final mechanical plans for the antenna and was wondering if
there is any consensus with regard to insulated parasitic elements. The 
2" OD elements I'm using fit nicely into Electrical UV resistant PVC 
which would allow for insulating the elements from the mast.  I also 
thought it would aid in final tuning if I utilized a small amount of 
inductance at the center of the director and reflector to fine tune 
those elements.
Thoughts welcome,
Dave
Wa3gin
P.S. boom 48ft., Full-size or slightly less to accommodate center tuning
coil inductance.
------------------------------
Message: 2
Date: Mon, 21 Sep 2009 12:34:43 -0500
From: "Stan Stockton" <k5go at cox.net>
Subject: Re: [TowerTalk] HB 3 ele 40m Beam
To: "David Jordan" <wa3gin at comcast.net>,	<towertalk at contesting.com>
Message-ID: <248A0EF1DFCD476FBB005D2077C5A761 at n42qnuurv8xdmc>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original
Dave,

My strong opinion is that if you use a good modeling program you can
build it and put it up without any need for adjustment.  Also, in order
to add the inductor you will need to not only insulate those elements
but split the halves as well.  I think the potential problems as a
result of having another thing that could go wrong outweigh the
potential benefit of being able to do some tuning at the center of the
element.

My elements are all insulated using element plates made from G10.  The
driven element is also split using a solid rod of fiberglass.

With elements that start at 2 inches OD, you will need to have some
pretty good trusses, depending on how much wind and ice you want it to
handle.

Stan, K5GO


Message: 3
Date: Mon, 21 Sep 2009 14:00:03 -0400
From: "David  Thompson" <thompson at mindspring.com>
Subject: Re: [TowerTalk] HB 3 ele 40m Beam
To: "Stan Stockton" <k5go at cox.net>, "David Jordan"
	<wa3gin at comcast.net>,	<towertalk at contesting.com>
Message-ID: <007901ca3ae5$5e1d22d0$f45f9a04 at yourxb2x7j77gn>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

Be careful.  The antenna modeling program is great when you don't have
interaction.  I finally decided to build a 12 meter beam in 1992 and put
together a W2PV 3 el that looked great that was to mount 5.5 feet below the
KT-34XA.  Well up it went and the antenna was centered on 24.500 not 24.930
plus the KT-34XA 10 and 15 shifted too.

I pulled that down and was reading the material Brice W9PNE had 
published on
a 2 el X beam.  I was familiar with the X beam as Dick Bird G4ZU designed
that along with his G4ZU birdcage quad.  Moxen and others stated the problem
with the X beam was side radiation.  Brice came up with side back wires and
his design calculations are in one of the first ARRL Antenna Compendiums.  I
used the lower spider and aluminum from the G4ZU birdcage, cut the antenna
to 24930, used a Collins coax balun and it came out to just above 24945 and
was below 1.2 across the narrow 12 meter band.  Changed the 10 meter
frequency on the KT-34XA slightly (both in SWR reading and on the MFJ 259
analyzer.  15 stayed right on 21.200 as before.  My DXCC count went from 
114
in 1992 to 320 today.

There used to be a program by K6STI that also modeled interaction and this
would be needed too
if other antennas are nearby.  I had to put the X beam where it is and the
alternative was to continue using the 40 meter beam with its cloverleaf all
or virtually nothing pattern.

73 Dave K4JRB