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?

Is there a way to minimize or eliminate the oscillator frequency
change when the counter is connected? My frequency counter is a Protek
B-818.