[Hallicrafters] Inductance measurements

[Roy Morgan]

At 02:02 PM 12/2/2005, Waldo Magnuson wrote:
>Hi Ed,
>    I have a Tektronix Type 130 L-C meter which does a good job of 
> measuring small-value L and C.  Inductance measurements are from about 
> 0.1 uH to 300 uH and capacitance from about 0.1 pF to 300 pF.  In both 
> cases 300 is the maximum value.  If you can't find a way to measure your 
> RF chokes I'll be glad to do it for you - no cost.

Skip,

Noble to offer..

I have not used one of those Tek LC meters, but it sounds just right for 
the lower valued coils and capacitors.  As I understand it, measuring such 
small values at audio frequencies and then using them in RF (HF) circuits 
leads to no big difficulties: the differences in actual value from audio to 
HF frequencies are very slight.

RF chokes such as the common 2.5 mH ones would need to be measured by 
indirect methods on your meter: measure a 250 uH one, then parallel the 
larger one, and compute based on the parallel value of the combination.

For measuring R, L, and C over a wide range of values, the Heath RLC meter 
works ok. Far better is the General Radio 650A bridge - an antique in 
wooden case but still offered on the auction place from time to time. This 
thing is not easy to operate, but it's a joy once you get used to it.

Better yet is the GR 1650A (or later B). It does all the earlier bridge 
does and a bit more, is much smaller, more portable, and somewhat more 
accurate.

GR made many other bridges, many of them more accurate than hams and 
experimenters *need*, and some dedicated to R, L, or C.  Some of them are 
not easy to run, and need external signal source and detectors. I have some 
of these.

For some $100 or so you can buy a modern, solly state, automatic gadget the 
size of a DMM that does it all.  I've recently seen one that baffles me 
with complexity. It's plenty accurate and measures most anything.  (Do 
*you* know what a milli Seimens is?)  I'm sure you do know what to do with 
it the day it does not work right anymore.

We have not yet mentioned the old standby: the grid dip meter. In it's many 
incarnations, from the very fine military PRM-10 and Measurements 
Corporation Megacycle Meter, to the much more handy EICO, Heath and Millen 
units, these things can be made to get results plenty good for ham work. 
They don't measure audio chokes and the like, though.

I like the old classic stuff. At my place it is both much appreciated and 
repairable.

Roy




- Roy Morgan
National Institute of Standards and Technology
100 Bureau Drive, Stop 8970
Gaithersburg  MD 20899-8970
Voice: 301-975-3254  Fax: 301-948-6213
E-mail:  roy.morgan at nist.gov --