[TowerTalk] 259 Dip Coils

[Tom Rauch]

> I have just ordered the tuning stubs for the MFJ 259
analyzer. I believe  one
> or more of the traps on my A3S may have gone south.

I'd NEVER try to dip anything with those things that modify
a 259 to be a "dip meter".
It's one of the poorest products I've ever seen.

It was copied from a QST article (that I think won an
award!) but it's a bad idea. In a regular dip meter the coil
is part of an oscillating resonant circuit and has extremely
high flux levels surrounding the coil. This allows it to
couple to things around it with very good coupling even at a
modest distance. In the antenna analyzer, the coils have
very low flux density and have to be coupled so tightly to
whatever you are measuring they hose up the resonance of the
thing you are testing.

It's actually more accurate to use a T connector, a dummy
load, a small 12V light bulb, and a hunk of PC board or some
other groundplane to measure trap resonance.

Run a rig through a T connector to a dummy load. Tap off the
center pin of the T with a small 12V bulb, and go to one end
of the trap. Ground the other end of the trap to the
groundplane.  Ground the shell of the T to the groundplane.
Turn up power until the light lights, and sweep frequency
for dimmest light. That's where the trap is parallel
resonant. Works as good as a network analyzer for finding
parallel resonance.

73 Tom