Andreu wrote:
I have several small measuring instruments in my shack, but I have
always been unable to find plans to build a DIP METER for use in
LF Freqs. I already have a LEADER DM that begins at 1.5 Mhz but I
would like to be able to measure resonant circuits at say 40 Khz
or 470 Khz. Is there a thecnical difficulty I should be aware of ?
Any help or reference appreciated.

Andrew.


I've built a few dip meters, most with the circuit using a dual
gang variable cap. The Millen dip meter is the same circuit.
The variable caps are usually around 100 to 200pf per section
giving a total tuning range of 50 to 100pf across the coil.

This works well up to about 1mhz tops, below that feedback
drops off as the reactance of the variable cap is too low.
IF the tuned circuit is ac coupled to the tube (plate blocking
cap in place) you can ground the center of the coil to provide
additional feedback. The Millen coils DO have a third pin
for this purpose. (My dipmeters used the 'Heath' method of
an RCA plug for the coil connecter so they lacked the means
of providing the ground).

My coils were wound on 3/8" dia plastic tubing (like Heath)
and I could get down to about 2mhz with a single layer coil
wound with #36 wire. To get down to where you want to go
will require a larger diameter coil form, and a "Pi" winding
(like on rf chokes). Litz wire would also be a good idea.
The tuning range even with a 200pf / section variable cap
will be less than a 2/1 frequency range due to distributed
capacitance across the coil. Coupling should not be a problem,
if you can get the dip coil close enough to the inductor in the
circuit under question. This is where a small dip coil has an
advantage....Try getting those Millen coils close enough to
a modern solid state circuit!

Surf my web site (www.qsl.net/wa2mze) to see my mini gdo built
with a 6cw4 tube.