[TowerTalk] Trap resonance - Down Under

[Peter Cattell]

Gi'day from down under again,

Thanks to all those who gave me (a newcomer to all this) advice.  Most said
to shove the Dip Meter coil up the hot end of the trap after removing it
from the antenna and look for a dip.  Perhaps I have an insensitive DM but
in no way could I get a dip this way.  In any case, removing the black
sealing cap from inside the hot end tube to enable entry of the DM coil was
very difficult.  I tried blowing and sucking with 2 vacuum cleaners after
sealing all holes with no success and finally had to just about destroy it
to get it out!

I then remembered an old article I read about traps that was aiming to give
advice on how to work out their resonant freg. when you have no fancy
equipment.  It said to connect the output coax from the back of the
transceiver to hook up wire and form a loop from the centre (yep - that's
how we spell it down here) conductor to shield, wrap about 3 turns of this
around the trap hot end, and place a fluro tube next to the trap and using
very low power look for slight lighting of the tube as the transmitter freg
is altered. I figured this was fairly safe with my TS 690S seeing it should
shut off prior to any damage to the finals - hopefully!!

I modified this procedure after reading the instructions that came with the
DM about using it as an absorption meter (in the OSC/OFF position) instead
of the fluro.  I found 2-3 watts was sufficient to get almost full
deflection of the meter (with the DM coil just outside the position of the
nasty seal I had just taken 1/2 hour to remove!) and altered the DM
rotating dial to get a max and then the transmitter freg to get a bigger
max and iterated this until both adjustments gave a combined max.  The DM
read 20.25, the Tx read approx 21.060 (+/- .020) for both 15m reflector
traps so I guess both traps are OK!  I take it that the Tx read-out is more
accurate than the DM and that both resonate at about 21.060.

Is this procedure reliable if you can't get a dip using the instrument in
its Dip Meter function?  If not, is there another way short of spending yet
more money on testing equipment?  (My wife is starting to add up the
dollars!).

Peter



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