Reg Edwards wrote:
There are inumerable uses for solenoidal wound coils.

Over the years there have been been hundreds of discussions and
contributions to newsgroups about the Q of single-layer solenoid
coils. But what is ENTIRELY missing is the measured data for
particular coil dimensions and frequency.

Does nobody have a Q meter? It would appear nobody has any confidence
in Q meters in the HF range.

I just purchased an old Boonton 160A Q meter that seems to still be
working, correctly. It supplys test waves from 50kHz to 75 MHz.

It was made in 1949 (the same year I was), is a 3 tube design,
including the supply rectifier, and probably last calibrated when I
was wearing diapers, but everything on it still seems okay. I have
been using it to compare different coil and ferrite rod designs to
improve my ability to build optimal rod antennas.

QUESTION:

What is the measuring accuracy of the best commercial Q meters in the
ranges of 1 to 100, 100 to 500, 500 to 2000 and above?

Absolute accuracy is hard to quantify, because the connection losses,
radiation losses and near field losses vary a lot, depending of the
setup. The 160A has made a valiant attempt to have a low loss tuning
capacitor available to resonate the coil at various frequencies, but
if I pad this with an external capacitor, I never achieve as high a Q
reading as I do with just the internal cap. The best I can do is
compare variations with a single setup. In other words, if i can make
two tests with a single setup, I can clearly tell which variation has
the higher Q. But if I sit closer or further away from a large coil,
it changes both results. At high Q, very little things count a lot.
Measuring a large coil that is 6 inchs from any metal surface, and
then putting it in a metal box, an inch from the side, kills the Q,
anyway.

The scale on the 160A ranges from 20 to 200, but you can double that
with another setting that cuts the excitation. However, at Qs above
100, the tuning is so touchy that I often can't find the exact peak.

Or do not manufacturers state measuring accuracy? Are they themselves
uncertain of what its all about?

A subsidiary question is what use is made of Q values after a
measurement has been made? Does an inacurate Q value matter very much
anyway?

For tuning and filter purposes, it predicts the bandwidth. For rod
antenna purposes, Q gets into the region of space the antenna couples
to. The higher the Q, the larger volume of space the antenna pulls
energy from.

I have also had some success at low frequency (below 1 MHz) measuring
tank Q by driving the tank through a 10X scope probe, and measuring
the resonant voltage with an AC volt meter through a second 10X scope
probe. I find the frequency that produces the peak voltage, then tune
up and down to find the two frequencies that produce .707 of that
peak. The Q is the square root of the product of those two
frequencies divided by their difference. I don't know if it is the
loading effect of the probes, or lack of calibration for the Boonton,
but I consistently get lower Q by this method than the Boonton shows.
The Boonton may be 1.2 to 1.5 times higher. But, at least both
methods allow comparison of variations, so I can have a "getting
warmer" indication of which variations are better.