[TowerTalk] FW: Hy-gain 204BA element changes...

[Joe Subich, W4TV]

Running the scenario in YO results in a change to the tip lengths
of less than 1/16" to maintain the same resonance.

Shortening the 1.125" tube by 1" and lengthening the .875"
tube by 1" require the element tips be shortened by less that
0.02" each.  If the 7/8" tube is lengthened by 15/16" the tips
need to be lengthened by 0.05" each.  Either change in required
tip length less than the accumulated tolerances of the other
measurements in assembling the antenna.

In this case, I would increase the overlap of the 1.25" joint
and decrease the overlap of the 7/8" joint by 1" each and not
give it another thought.

73,

    ... Joe, W4TV



> -----Original Message-----
> From: towertalk-bounces at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Dino Darling
> Sent: Friday, February 17, 2006 11:07 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Hy-gain 204BA element changes...
>
>
> I have an older Hy-gain 4-element 20 meter mono band beam.  I
> downloaded the LJ-204BA manual from the Hy-gain (MFJ) website.  I
> took the antenna apart and verified that all the element lengths are
> the same in the manual.  Other than a different style hairpin, my
> older antenna is identical to the current version.
>
> Hy-gain makes use of swagged element tips.  I have a slight issue
> with the amount of overlap with the non-swagged elements
> closer in to the boom.
>
> I'm aware of the electrical characteristics of tapered elements and
> know you just can't shove one the second element in and extra inch
> and make up for it by pulling out the third element an inch.  The
> diameter of the tubing effects the electrical length of that
> half-element.
>
> Well, understanding, and knowing how to compensate for changes, is
> two different things and I could use your help.
>
> I can download a YAG file from the ARRL website
> (http://www.arrl.org/antmodels/), but need YO to play with it.  I
> believe YO compensates for tapers.  I don't have a NEC file
> of this antenna.
>
> So let me get specific...
>
> The second tube out from the boom (for all eight half-elements) is 1
> 1/8" x 48".  The instructions call for 46" exposed.  This leaves only
> 2" inside the 1 1/4" tube!  The 1 1/4" tube is NOT swagged.  The
> third tube out is 7/8" x 55".  The instructions calls for 50 1/2"
> exposed.  This leaves 4 1/2" inside the 1 1/8" swagged tube.  Here is
> the thing though, the 1 1/8" tube is swagged for the first 2".  The
> remainder 2 1/2" of the 7/8" tube if just floating inside the
> 1 1/8" tube!
>
> What I would like to do is move the 1 1/8" tube in one additional
> inch (3" overlap instead of 2") and compensate for the shorter
> half-element by pulling the 7/8" out...but by how much, I don't
> know.  I have 2 1/2" to play with since it is only floating in
> air.  This is where I need your help!  I do know that 1" of 1 1/8
> requires more than 1" of 7/8" to compensate.
>
> The rest of the elements have enough overlap per diameter.  My issue
> is that there is a lot of weight on only 2" of the 1 1/8" tube!  It's
> a good argument to say this is the way it's been done for years, so
> why mess with it.  My 1 1/8" tubes are bent at the 2" mark and I'd
> guess it would be better if there was a bit more overlap.
>
> One of these days I may get a copy of YO and learn to use it, or
> build a NEC file for use in Eznec, but for now, I'm useless!  :-)
>
> Dino...k6rix at earthlink.net
>
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