On Oct 5, 3:37*pm, "Jerrold Jones" wrote:
I have a project where I am going to modify an internal receiver circuit
that uses Toko style coils for the various stages. *I want to be able to
determine the resonant frequency of these coils. *I'm told I can do this
with a dip meter, but I'm not sure how. *The Toko coils are shielded. *If I
just bring the dip meter coil near, I don't get a response. *Am I going to
have to remove the Toko coils from the circuit, remove the metal shield, and
then move the dip meter close and adjust for the dip or is there a simpler
way?

Thanks in advance,
Jer

Are they just coils that you resonate with an external capacitance, or
do they include capacitors? If they are coils, you should be able to
resonate them with an external capacitor, and leave the leads long
enough (formed in a loop) to couple to the GDO. The leads add some
inductance that you can at least estimate and subtract out. If you
can't couple closely enough with a single turn loop like that, you can
use multiple turns, again estimating or measuring the inductance of
those turns and subtracting it out.

If the shield cans also contain capacitors (as is typical for IF
transformers), things get more complicated...

Removing the shield can is probably not a good idea. If the coil
inside is open (doesn't have a powdered iron tube around it), then the
inductance of the coil will be somewhat lowered when it's inside the
shield. If the coil inside does have a powdered iron tube around it,
you may not be able to couple well enough to the coil to measure it.

You may also have other ways to measure the coil/resonator...you can
do a lot even with a general-coverage receiver.

Cheers,
Tom