Yaesu FT-902DM Instruction Manual - page 2
Question #2: How to interface the x-lock to the rig ?? The minimalist approach is to sample the RF
input from the Counter unit and wire the control voltage to the RIT line. Tried both and FAILED
miserably .... Most likely because the composite frequency presented at the counter input is
inversely related to the VFO frequency !! he he That way the stabilizer instead of stabilizing the
drift, made it worse!
Anyway, the minimalist approach as simple and innocent as it seems is neither and most of all does
not work.
Reluctantly then decided to try the real thing: getting my hands into the heart of the VFO ... And
indeed this proved to be both easier, less risky and much more tidier approach. Most of all it
WORKED beautifully!
First of all, one must remove the VFO assembly from the rig. Carefully done is straight forward. It
would be very useful, before removing the vfo, to align its analog dial according to the digital
frequency display, and be careful not to disturb the analog dial throughout the modification process.
This will be the indicator of the frequency difference imposed by the presence of the x-lock varicap
circuit (1n4004 and 1pF in series and parallel to TC801).
More on that later.
After extracting the VFO, remove its aluminum cover. You can identify the main tuning variable
cap, above it the vfo board and in the back the coil and a second variable cap TC801. This cap is
used to adjust the linearity of the analog scale in the vfo, and that is where the varicap circuit of the
stabilizer should be installed.