[TowerTalk] Re:TowerTalk] Cushcraft A3 help

[Tom H]

> A CC A3 followed me home from the swap meet yesterday and I need a
> bit of information, if someone could help.  I have downloaded the
> manual from CC Web page, but I still have a question.  It seems that
> there is a difference in the 15 mtr traps, 4 being alike and 2 being
> different (the ones for the director). Well looking at them I can
> find no markings and they look identical. So how do you tell them
> apart ??????
>
 Hiya Art,

 When your A3 was new, the traps had a paper sticker indicating which was
which.  Why the traps weren't engraved or marked with a permanant sticker is
a mystery that only CC can answer.  Funny, I had an A3 follow me home from
Dayton on the roof of our van whereupon I discovered I was in the same
situation as you.  You have a couple of choices.  Taking them apart though
is not one of them though! Inside, they still look the same.

 1) Atach them using very short leads to a HP network analyzer and punch up
 the Smith chart.  Start around 18 Mhz , and crank the frequency up until
the
 readout on the display switches from inductance to capacitance.  Note that
 frequency.  You will find 2 whose frequency is about 150Kz higher than the
 other 4.  Not everyone has a 100 grand piece of equipment at their disposal
 though, so try method #2.

 2) Use a grid dip meter placed end to end on a non-conductive table to
 determine which 2 resonate higher that the other 4.  This was very
difficult
 for me to do considering the small difference in frequency you have to look
 for.  Using this method initially, I picked the wrong ones.  The network
 analyzer was a much better approach.

 Calls to Cushcraft went unreturned, but I did get this responce via e-mail:

 "The traps of the A3 and A3S can only be separated one way. First of all,
 the 10 meter traps are the same and you can use them in any position. Be
 sure the end with the contact screw for the body to element junction is
 nearest the boom. The 15 meter traps can be identified by the fact that
 they are "swagged" to a smaller tubing size on the outboard side. There are
 2 different types of 15 meter traps. 4 of the traps are used in the
 reflector and driver elements. There are two 15 meter traps that are used
 in the director and they have a higher frequency of resonance. That is the
 only way to tell the difference. Check the traps with a dip meter and that
 should tell you which are which."

 Real technical, huh?

 According to an aquaitance who is a former CC employee, they used to
perform
 this service often for a nominal fee, but it dosen't look like they do this
 anymore.

 Wichever way you try, Art, you're going to find a different resonant
 frequency for each trap.  They aren't all the same.  Also, the traps on an
 assembled antenna resonate at a different frequency than when they're
 sitting out separately on a bench. So, don't be alarmed if you see them
 resonate outside (lower) the 15M band.  Good luck to you.

 7 3,
 Tom K3GM
 http://users.snip.net/~biskit/thomas_j.htm



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