Measure the voltage from one of the three pins circled with blue color.
On receiver VCO (VX) card the tuning voltage is present on the leftmost (3)
and on the transmitter VCO (VZ) card it is on the rightmost pin (1).
If the tuning voltages are not satisfactory on the whole of desired frequency range,
you can raise the voltage by disconnecting the feedthroughs one by one on the
stub lines (circled with red). Do not drill the hole through the pcb.
To lower the voltage you can reattach the feedthrough to the ground plane.