Jim Yanik wrote:

On Thu, 30 Apr 2009 07:23:28 -0400, Michael
wrote:

Hi,
I regularly repair and restore vintage CB and ham radios. Older CB
radios often have had their crystals drift off frequency usually to a
lower frequency. When I use my frequency counter to align the crystal
back to it's intended frequency via a trimmer capacitor the frequency
changes as soon as I connect the counter. In other words what good
does it do to adjust the PLL reference oscillator to 10.240 MHz if the
frequency changes slightly when I disconnect the frequency counter?

snip

Using a scope with a 10X probe or FET probe may decrease the loading,if you
have a CH.1 output to pass to the counter.
Or perhaps a pickup loop might give a smaller load on the osc.

When a pickup coil doesn't provide enough signal, I use a broadband CATV
distribution amp (~1MHz - ~900MHz) which has surprisingly flat response
and can also be useful as a scope preamp. These are often found cheaply
at hamfests, local e-waste dumps, or from cable TV plants (shmoozing
required). Use with a pickup coil or tank circuit on the input.

Michael