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

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

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

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

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.