There are two possible points (two green arrows) for controlling the Reference Oscillator. The
point with the dark green arrow should be more sensitive. Connect the NPN transistor with
Collector to whichever of these points you choose, and Emitter to ground.
Using thick double-sided foam adhesive tape, mount the XRef board either on top of a shielded
box or in some other suitable location near the Reference Oscillator.
Mount the board with the Ref/RF/Ctl connections closest to the Reference Oscillator area. The
XRef connection pads are double-sided, so check that the underside pads aren’t shorting to the
shielded box.
The next step involves soldering three short lengths of fine hookup wire to each of the
connection points circled in Figure 3. With a very fine tip soldering iron, it is possible to do this
with the board in place. Be very careful not to overheat the components as they can be easily
damaged. I normally apply a small blob of “normal” (i.e. not lead-free) solder to the connection
point first, and then attach the already-tinned wire.
Attach the wires to the XRef as follows:
Blue
connection to RF pin.
The base of the NPN transistor to Ctl pin.
Red
connection to Vin pin.
Also connect a wire from the XRef Gnd pin to a nearby earth connection, like the tin shield.
Finally, we need to bring 10 MHz in to the XRef. Mount a suitable connector on the back panel
of the radio and run some thin coax to the XRef.
Optionally, an LED can be connected from the XRef Lock pin to ground to indicate when the
radio is locked to 10 MHz. The LED could be mounted next to the connector on the back panel.
Before putting everything back together, carry out some basic tests.
With 10 MHz NOT connected, turn the radio on, select SSB mode and a higher band, and
tune to a beacon or carrier.
Adjust the Ref Freq Adjust control up and down and you should hear the beacon tone
change indicating the Reference Frequency is changing.
With Ref Freq Adjust set to say 75% of its travel, connect 10 MHz and you should hear the
beacon tone jump slightly. If there is no jump, try again with a setting of 25%. The radio
should now be frequency locked.
Finally, re-assemble the radio in the reverse order and enjoy your new frequency accuracy and
stability!
5. Operation
The board continually tests for the presence of the external reference. If 10 MHz is removed,
the XRef-PLL will automatically disconnect from the radio, leaving the radio to operate as
standard.
If you notice a warble on the signal indicating a marginal PLL lock, try altering the Ref Adjust
setting so that there is very little change in the radio’s frequency with 10 MHz connected or not.
The 10 MHz source can be a sine or square wave, but it is important that it is clean. The board
is, in effect, adjusting the radio’s Reference in step with the incoming 10 MHz, including
whatever imperfections there may be. The old adage
garbage-in, garbage-out
applies here.
6. Support
If you have any difficulties, you can contact David Smith VK3HZ by email :
