[TowerTalk] Cap/Inductance meter

[Jim Lux]

At 12:56 PM 4/5/2007, jacobsen_5 at msn.com wrote:
>Has anyone any info on capacitance/inductance meters? A google 
>search turned up a  PROTEK CL200. I can't seem to find any reviews 
>on it or any others. Would seem that it would greatly speed up 
>antenna set up for home brewers. You could use a variable broadcast 
>type cap to set up a shunt feed for a tower or trap, read it with 
>meter, and then substitute fixed doorknobs. The same with coils. 
>Just a thought. (Few and far between at my age)

A lot of inexpensive DMMs these days have C or L measurement capability.

The problem with most L and C meters is that the measurement 
frequency is very different from where you'll be actually using the 
component, so things like parasitics can really change the effective values.

Imagine, for instance, measuring a 40 uH coil with a few pF of shunt 
C.  At 1kHz (a typical low frequency for L and C meters), the few pF 
is nonexistent, but at 10 MHz, it's definitely an issue.

Something like a RF impedance bridge (which can use an excitation at 
your actual frequency) would be good.  One of the ubiquitous MFJ 
antenna analyzers could also work.  If you're working with a C, you 
can put a fixed series L in the circuit to bring the Z into an area 
where the MFJ works better.  Especially since you're just looking to 
match a variable device with an array of fixed, absolute accuracy isn't needed.

Jim, W6RMK