On 10/06/2011 06:51 AM, Jerrold Jones wrote:
Yes, I have the original coil specs, but only in frequency and the
schematics do show whether they are coil only or have an internal
capacitor present. The problem I'm facing is that I know the new
frequency I want to use, which is about half as high as the current
frequency, but I don't know how to figure out the correct number of new
windings I'll need. The coils are all Toko in shielded cans, so there
are a lot of unknowns. Even knowing the frequencies they are on now, I
still haven't been able to measure it and that is where I must start. I
guess if I have to remove each one, break the internal capactor, and
then form a loop around the dip meter coil with a new cap in parallel
with the coil, I could, but I was hoping for a simpler way.

Jer


"Michael Black" wrote in message
mple.net...
On Wed, 5 Oct 2011, 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?

So if it's a commercial receiver, the information may already be out
there, but nobody would know until you reveal the receiver, and the
stage you want to modify.

Michael VE2BVW


If you have an L/C meter or bridge you can connect the unknown shielded
coil in series with an inductor of known value and measure the two in
series. Then subtract the known inductance from the reading. (works
for coil without parallel capacitor). For a parallel LC combo with a
bridge you can measure the combined L C reactances at different
frequencies and work out the L and C values, but the math is a bit involved.