Notes on installing the Cumbria Designs
X-Lock 3 into the Kenwood TS120S Amateur Bands Transceiver.
Roger Wincer, ZL2RX
Varactor Coupling Capacitance
varactor circuit to the VFO was fairly simple once I had established the
coupling capacitance values. The coupling capacitor to the correction
varactor circuit consists of two 5.6pf capacitors in series and connects
to the hot side of C17 and C18. This arrangement required only a
relatively small adjustment to L9 to bring the dial setting back to
original. Using more coupling capacitance than the 2pf or so that I used
may result in some warbling of the received and transmitted signals. As
I am using my TS120S with WSPR slow data mode and as WSPR is very
sensitive to any type of frequency shifting, I set the X-Lock's "Correction Rate" to minimise the "warbling" effect of the correction
process. I had previously removed C18 (15pf) and C18 (12pf) from the
VFO in an unsuccessful attempt to stop temperature drift, these were
replaced these with 18pf and 5.6pf capacitors to restore the VFO circuit
to it's original state. These capacitors are in parallel across the main
tuning circuit which includes TC1, L9 and the main tuning capacitor.
(Note: In an unmodified rig C17 and C18 should not need
to be changed).
The varactor diode circuit was mounted to the
VFO by using an old recycled 3 terminal tag-strip soldered to the
chassis. The RF output was taken from the back of the VFO RF output
socket using a screened wire. There was a handy hole in the rear of the
VFO outer screen for the two wires for the X-Lock board.
Mounting the X-lock board is tricky as there a
no spare space in the rig, so the loudspeaker had to be sacrificed! The
board was hot glued into place using thin cardboard spacers as can be
seen in the photograph. The power was taken from the cold end of R14 the
large 2 watt resistor on the AF Gen board, as this point provided about
+11.5 volts. I had to solder connections directly onto the plug socket
inputs because there is no headroom for the plugs! Any movable wires and
solder joints were stabilised with hot glue to prevent shorts etc. One
more advantage of removing the speaker is that the indicator LED can be
monitored from outside the rig, through the gauze cloth.
I have tested the rig
on transmit and receive using WSPR and it appears to work wonderfully
well and is stable day after day after day. I have also used it on CW
mode where the Tx frequency is shifted 800 Hz from the Rx frequency and
it works flawlessly. I have set the "post tuning" to about 8 seconds,
which seems a reasonable time.