[Test-Equipment] Test Equipment 101: measuring the variable cap

[Ron W4BIN]

On 9/18/22 11:27 AM, Doug Hensley wrote:

>  From time to time I wonder about the capacitance value of a vintage
> variable capacitor: the multi-plate unit typically used in receivers.  Seems
> like the older the receiver (sort of) the more plates the cap has.

   Back when tubes had plate caps the coil was wound in slots in the 
back panel,
made of Masonite.  That wasn't much inductance so it took a lot of 
capacitance
to resonate at one mega-cycle. (plus and minus half a mega-cycle)
As progress marched on ferrite antennas created much more inductance so 
less
capacitance was needed to resonate at one mega-cycle (plus and minus 
half a mega-cycle)
and many in between variations.

> My Dah-shing "measures all" unit usually repeats the value printed on
> a good electrolytic or disk ceramin. When it comes to the variable cap,
> I am not sure at all.
>
> Input from someone whose "been there, done that" please 🙂 ....

   In addition to the "measure all semiconductor" testers my VNA measures
the capacitance of any part that I connect it to, nicely.
-- 

    Ron  W4BIN - Understanding is much better than
                                       knowing how.MX