Hi David:

It is hard to tell from the facts you gave us. It might be useful to feed a
signal generator into the scope and compare to factory specifications. The
1 pf coupling capacitor could be less capacitance, and simply let less
signal through. Or, your RG-62 could be lossier that expected.

I assume the input to the SB-610 is properly tuned to the correct frequency,
since there were different "front ends" available for the SB-610. If the
front end is not tuned properly, then the indications of the SB-610 will be
misleading, even though you have increased the gain.

73, Colin K7FM