[Elecraft] Testing traps with a GDO

[Don Wilhelm]

Dan,

I don't know the specifics of that antena, but traps are quite similar
electrically (a parallel tuned circuit) - so here are some guidelines.

First, you must be able to couple the GDO coil to the trap coil to obtain a
dip - some traps are enclosed in a metallic shield (part of the capacitor)
making coupling difficult while other traps have the coil exposed and
coupling is easy - just place the dipper coil parallel to the trap windings
and tune for the dip.

The trap must be removed from the antenna if you intend to measure the real
trap frequency - connection with the antenna elements will modify the trap's
measured resonant frequency.

OTOH, if you want to just perform a 'sanity' check, you can compare the
traps on each side of the antenna without disassembling things- the pairs
should be quite similar in resonant frequency readings even if the resonant
frequency is not that of the trap itself, and if you note a pair that is not
the same, you will know the problem lies in one of the two traps of that
pair - disassemble and measure both from that pair to determine the real
culprit.

There are methods other than a GDO to determine the resonant frequency of a
parallel tuned circuit, but you asked about the GDO specifically.

It is also possible to couple the GDO to the center of each antenna element
and determine that the trap dipole is resonant at the correct frequency.


73,
Don W3FPR

----- Original Message ----- 
>
> I know there are some pretty knowledgeable folks here so please allow me
> to tap some of that knowledge.
>
> I have a troublesome beam (TE-33) and I suspect one of the traps.  Being
> a tuned circuit, I would like to try using a GDO to check the trap's
> resonant frequency.
>
> I have found nothing on the Internet on how this is done.
>
> Can anyone tell me or, send me a link, on the correct technique for
> testing a trap?
>
> danl@internode.on.net
>
> Thanks in advance.
>