[600MRG] inductor measurements

[Edward R Cole]

Thanks everyone for comments and advice.

I looked on e-bay and there is a range of instruments listed.  The 
HP4342 is the Q-meter (not a 432) and a couple listed in the $450 
range.  Some old Boonton one's $100 and under but about $50 
shipping.  Some other modern meters in middle range $200+.

I noted that they range down to 50-KHz and up to 30-MHz (or 
higher).  Also apparently one needs calibration plug-ins for them.  I 
guess these are basically comparison bridges and probably one could 
build their own.  But like most commercial instruments stability is 
the key for good operation.  I recently obtained open/short/50-ohm 
calib terminations for power meter use and calibration of directional 
couplers (note: my ham operations go up to 10-GHz).

I really don't need one, at present, and do need to spend money on 
more important things (like repair of my MFJ analyzer which I use 
frequently).  I have the inverted-L successfully tuned using the MFJ 
and will need it to move from 495 down to 475 (-3/+4) KHz.  The 
Fwd/Ref power indications in the shack thru the RG-213 coal line from 
the base loading coil is different so I'm guessing their is common 
mode currents on the coax (It parallels one of the radials), though I 
did use four large ferrite beads on the coax (probably not near 
enough to choke <500 KHz).

Upgrading my Elecraft K3 to operate below 490-KHz cost me $468.95 but 
has other benefits other than just enabling operation down to 
100-KHz.  It benefits operation in highly crowded HF bands (which I 
don't do much) and lowered VFO phase noise which improves weak-signal 
performance (which I do).

It may even be at the PO today!

73, Ed - KL7uW

At 10:34 AM 9/28/2015, Rudy Severns wrote:
>Frank is right on the mark.
>
>
>
>You have to be careful when measuring inductor characteristics if you want
>accurate results.  If you have a Q-meter it's very instructive to mount the
>coil in place, measure the Q, and then place a sheet of copper board or
>aluminum at various distances around the coil.  When you place a conducting
>sheet close to the coil the Q-meter reading will drop dramatically but
>that's mostly detuning from resonance.  You have to re-peak the Q to see the
>actual effect on inductor Q.  You can also use this approach to check on
>coupling between coils, etc.  This can be of great help in selecting an
>enclosure and for layout within filters.  The Q-meter will also let you
>determine the inductance at a given frequency.  Even in an air wound core
>the inductance will vary with frequency and there will be issues with
>self-resonance.  This can be an issue with the large inductances needed for
>very small antennas.  The Q-meter is a multi-purpose tool.
>
>
>
>73, Rudy N6LF
>
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73, Ed - KL7UW
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