[Elecraft] I'm Stuck!- counter hints

[Martin AC6RM]

Thanks Stuart.  I got this message after I took that counter back (I
tested it against my 2M HT and it was about 50khz off!) and got a
different one.  The new one is a small hand-held unit with an antenna that
attaches through a BNC connector.  It also measures relative field
strength.  It was almost three times the price -- $149.95.  It goes from 1
mhz up to 1.3ghz.  They had another one that goes up to 20mhz -- a
desk-top unit -- but it was $249.95.  I opted for the small hand-held; it
seems like it would be generally more useful in the field.

I tested the little handheld counter against my 2M HT on 146.595 and it
shows it as 146.59497.  Taking this reading gave me a reasonable level of
confidence in its accuracy.

I attached some RG174 to a BNC connector and I will try laying the coax
near the 4mhz oscillator area on the control board -- I am trying to
calibrate that 4mhz reference oscillator.  But I'd also like to have a
probe for the counter.  I am making what I'm hoping will be a suitable
probe -- BNC to RG174 to 10pf capacitor to tip.  Will that work or should
I add the 1 meg ohm resistor?  The spec sheet for the new handheld counter
specifically states "max input: 15 dBm," but I am not sure how that value
relates to the dBm I am likely to encounter on the board.

Many thanks es 73,

Martin

> Counters need a high impedance probe to connect to some circuits and not
> pull the frequency. Probes of 1 meg ohm (X1 Scope probes) or make your
> own with a VOM probe with 1 meg ohm resistor in series at the tip.
> Twist the Red and black leads to avoid extraneous mag field loop, and
> pickup therefrom.
>
> Sometimes, cheap counters may not be sensitive enough.  Try another
> range setting in that case.  But, usually, a simple oscillator will leak
> enough frequency energy to be picked up by a simple wire laid near the
> board and connected to counter input as indirect (inductive or
> capacitive) coupling.
>
> It is easy to try something like the above, even a 100 k ohm resistor in
> probe before buying a more expensive counter.  Also, some DVM counter
> combinations do not cover higher than audio frequency (20 kHz) or maybe
> 1 MHz.  Check the specs on what you have for its sensitivity and
> frequency coverage.  Low end counters maybe be less sensitive, (need
> more signal) at higher frequencies.
> 72,
> Stuart K5KVH