In article om,
Jim Mueller wrote:
On Mon, 04 Jun 2012 21:54:11 +0000, Hank wrote:

Heathkit made a Q-meter kit that was patterned after
the Boonton, but simplified. I had one of these for years, and got
quite a bit of use out of it, but the 260A is a step up in capability
and accuracy.


Hank

Since you mentioned the Heathkit unit, I have one that I haven't done
anything with since I don't have the special inductor to calibrate it. I
also don't have any way to measure an ordinary inductor to use as a
substitute. Do you know of some other way to calibrate it?

If you've got the unit, you can use a 455 khz IF transformer to check
out its functionality. Most of these used in AA5's had coil Q around
100. There are probably ten or twenty different ways to getting a
reasonable calibration, depending on what other test equipment you
have available and your knowledge and skill in methodologies for using
them. Also consider what your intended use of the Q-meter is. For
getting front-end coils and IF transformers in a receiver you are
bringing back to life, your primary need is to find coil inductance
and whether the Q is "reasonable" or "not reasonable." There is a
good discussion of Q measurements and a section on Q meters and their
vagaries in Terman and Pettit "Electronic Measurements" (2nd ed.,
McGraw-Hill, 1952). What that makes clear is that absolute
measurements with a Q meter have enough error that they're only
indicative of in-circuit performance.

Your first calibration point is to set up the injection oscillator.
That's a frequency measurement, traceable to NIST through WWV.
The second calibration point is the tracking of the resonating
capacitor to the panel calibrations.
The third calibration point is the oscillator injection voltage
across the metering resistor.
The fourth calibration point is the voltage developed across the coil
at resonance. "Q" is the ratio of that voltage to the injection
voltage.

If you've got something like an RF VTVM available, you can measure the
two voltages directly. You probably are not going to want to go
through the gyrations needed to refer anything but the frequency
measurement back to NIST.

A quick search on the net with Duckduckgo came up with this link:
http://www.jamminpower.com/main/260A.html
It's got links to 260A user and calibration manuals. The Heath unit
is a cheap knock-off of the Boonton design, so the Boonton material
generally applies to it. The Heath unit is quite adequate for
repair bench work. The unit I had did yeoman service before I got the
first 260A. While mine came with the standard coil, it got its
calibration checks with nothing better than a Tek 547 scope and
Tek signal generator, with a variety of coils used as a cross-check.

Hank

Thanks for the suggestions and especially the links to more information.
I haven't had time to read them yet but I did download and save them for
when that time comes. A quick glance at them already gave ideas on how
to get my meter going without a standard inductor, although that method
would be much easier!


--
Jim Mueller

To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.