On Sun, 12 Sep 1999 08:36:12 -0700 Arthur Moe <kb7ww@chatusa.com> writes:
>
>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 ??????
>
>
>Thanks for any help
>
>Art
>KB7WW
I asked the same question about a year ago, and below are
excerpts from two messages on the subject. Cushcraft does
NOT recommend disassembly of the traps, so the best way is
to use the dip meter. You want to have the coil of the dip
meter as parallel as possible to the coil in the trap, but
you will probably be forced to tilt it off axis a little
because aluminum tubing gets in the way of the case of the
dipmeter.
Dave Hachadorian, K6LL
San Diego, CA
K6LL@juno.com
----------------------------------------------------------------
Even though the 15 meter Tb and Tc look the same and have the same 31
turns , there are two ways to identify them. First use the Grid Dip
Meter and carefully compare the dip frequency of all six 15 m traps.
There are 4 Tc and 2 Tb traps; the Tb's for the director only. You will
find the two Tb traps tune 200 Khz higher in frequency than the Tc's.
If you take them apart (prefer the first method), you will see the only
difference is the overlap of the outer sleeve and the inner tube. There
is 6.5" for the Tc and 6.0" for the Tb. That little bit of difference
in the overlap changes the resonant frequency by the measured 200 Khz.
I measured, for reference on the Millen GDM, 18.05 Mhz for the Tc and
18.25 Mhz for the Tb. The Ta, 10 meter, trap tuned near 24.7 Mhz on
meter. The Millen, however, was not checked for frequency accuracy, but
I was satisfied with being able to measure the change. Also all traps
have there "shorted" end assembled nearest the boom.
All you need to do is lay the open
end of the trap to the end of the Grid Dip Meter coil and tune for the
dip. This means the trap and the GDM coil are on the axis. I was amazed
at the sensitivity of this measurement! I didn't bother to calibrate the
GDM for exact frequency; just compared the meter scale frequency from
one to the other and the sensitivity of the dip.
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