[Elecraft] Another K2 Capacitor Question....

[Ron D' Eau Claire]

Jonathan, K1RFD, wrote
> All of this discussion makes me think it would be great to have a
> capacitance meter on the bench, yet this is something most hams probably
> don't have.
>
> Has anyone seen a simple circuit which would allow capacitor values to be
> checked using, say, a signal source, an RF probe, and a DMM?  In other
> words, a "capacitance probe"?

Testing caps "in circuit" with some sort of probe is pretty hard since the
stray capacitance of the other components and PCB often exceed the value of
the capacitor being checked. More commonly a 'bad' capacitor is detected by
its effect on the overall operation of a circuit.

Out of the circuit, a capacitance checker is very useful. You may be right
that many Hams lack one although I have gotten used to a capacitance testing
feature in most modern DMM's. I have two DMM's and both of them, a Fluke and
a relatively inexpensive (about US $70) Radio Shack unit provide capacitance
checks. The Radio Shack meter does a good job on anything from electrolytics
of hundreds of microfarads down to values of a few pf, if you subtract the
stay capacitance reading of the meter itself.

So if you are thinking of upgrading your DMM, getting one with a built-in
capacitance meter might be the way to go.

Also, I've gotten "spoiled" by the newer DMMs that let me plug in an unknown
bipolar transistor and it immediately gives me both the hfe and the pinout!

Ron AC7AC
K2 # 1289