[Boatanchors] Tribander question

[manualman at juno.com]

If you can't repair the trap, you can buy a new one from MFJ/Hy-Gain for
$39.50.

If I remember correctly, the Mosley driven element mounting to the boom
is different then on the Hy-Gain. Also the feed system is different. If
you mounted the Mosley driven element by itself (as a rotatable dipole)
it probably would work reasonably well. Obviously there was certain
design criteria to create the Hy-Gain beam and all elements are part of
that design. Element length, trap design, thickness of the elements, the
spacing between the elements, and in your case the adjacent elements on
each side of the driven element are all important dimensional
considerations. You generally can't just drop another driven element from
another manufacturer in place of another driven element without doing a
lot diddling with all the rest of the elements. Unless, of course, you
don't care about gain and front-to-back ratio of this cobbled together
beam.

Personally, I would either try to fix the trap (there's not much in there
to go wrong) or just go buy a replacement unless you have lots of free
time to screw with this Frankenstein antenna.

Pete, wa2cwa

On Mon, 30 May 2016 18:37:43 -0600 RAY FRIESS <rayfrijr at msn.com> writes:
> I have a question for the group that I need advice and thoughts on.
> 
> This is a tale of two tribanders.   One is a Hygain Explorer 
> Tribander ... the other is a Mosley Classic 33.
> I've been using the Hygain for years, but now it appears one of the 
> traps has gone bad.
> The Mosley was sitting atop a 50 foot tower until a couple months 
> ago.   A friend of mine moved from Utah up to
> the panhandle of Idaho.  He still owns the house in Utah, and among 
> the things he left behind was the 50 foot tower
> with the Mosley on top of it.  A couple months ago, in a windstorm 
> packing winds up to 85 mph, the tower snapped at
> the base and came crashing down on top of the garage.  Luckily no 
> damage to the garage, but the tower, bent in a couple of
> places when it crashed down on the peaked garage.  The Mosley, of 
> course, took a whallop, but the driven element
> remained intact.  My friend told me I could have whatever of the 
> tower and antenna I could salvage.  (We'll save 
> about 40 feet of the tower).
> 
> My question is this....  What relationship do triband parasitic 
> elements (i.e. the reflector and director) have with
> the driven element, if any.  What I am wondering is, can I take the 
> driven element from the Mosley 3 element
> tribander and just put it in place of the driven element on the 
> Mosley, which has five elements on it.  
> If  you are familiar with the Explorer, it is a three element beam 
> with an RF coupled element a few inches in front
> of the driven element and one a few inches behind it, plus the usual 
> reflector and director at opposite ends of the boom.
> 
> Since the driven element of both beams is tuned (with traps) for 
> 10-15-20, my thinking is that what I propose should
> be okay.  But, I'm not sure if the distance of parasitic elements 
> from the driven element has any relationship to the
> type of driven element or if a beam's length is basically whatever 
> the designers decided they wanted the boom length
> to be.  Do reflectors and directors care what type of driven element 
> they are near as long as the driven element is
> resonant?  I know that there are formulas for how far apart elements 
> are to be from each other on a boom, but
> I think that's a function of boom length, rather than the type of 
> driven element.
> 
> Ray  WA7ITZ