[TowerTalk] Identifying Cushcraft A4 traps

[K3GM]

>
> Can anyone help in distinguishing between the 15m traps (TB vs. TC) and
the
> 10m traps (TD vs. TE)??  My e-mail request to Cushcraft stated that "we do
> not offer Trap diagnostics or identification as part of our Technical
> Support Service" and that I should use the book "Troubleshooting Antennas
> and Feedline", MFJ part number 3301 to help identify the trap.  Any advice
> or experience in how to do this?  Unfortunately Cushcraft does not mark
> their traps...  nor was the technical advice particularly insightful.
>
> -- Rich K1CC
>
Rich, the text below is the response I got from Cushcraft when I asked the
same question of the A3.   Cushcraft states that there is only one way to
determine which is which, and that is to use a grid dip meter.  Actually,
the best way is to put them on a HP network analyzer which is what I did.
The network analyzer revealed that I had chosen the wrong traps using the
grid dip method.  The problem I had with the grid dipper was that it was too
coarse to separate the minor differences in trap resonance frequency.  Just
remember that the director traps will resonate at a slightly (I mean
slightly!) higher frequency that the other ones.  Now, you have one more
element that I do, but just remember to put the higest resonating trap up
front, and work your way back.  To check the trap resonance, put the trap on
a non-conductive table, and place the grid dip meter against but not
touching the trap tube.  Don't be suprised if the traps seem to resonate at
a frequency other than what you expect them to,  My guess is that they must
interact with the rest of the antenna when it's assembled and on the tower.
BTW, according to a former Cushcraft engineer, they use to have a test
fixture which was used to find the correct traps for antenna owners who were
in the same predicament as you and I.  He told me that he suggested kapton
labels be used instead of the paper stickers, abut was voted down due to
costs.  I wish you luck in finding the right ones and hope you have access
to a network analyzer instead of resorting to the grid dip meter.  I can't
tell you how many time I have seen this question appear on the different
reflectors and news lists!  A simple plastic sticker or engraving mark at
the factory would easily solve the problem.

Tom K3GM

Cushcraft's "official" response:

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.



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