Cumbria Designs X-Lock

The X-Lock VFO Stabilizer kit that I ordered from Cumbria Designs arrived today. It is a Huff and Puff frequency stabilizer that is intended to be used to give long term frequency stability to older radios with non-synthesized radios, and it has been used with transceivers such as a TS-520. I hope to use it to cure the drift in my MFJ Cub.


As you can see from the picture above, it's a pretty small board, though it is about as tightly packed with components as it is possible to be. The X-Lock uses conventional leaded through-hold components, so no special skills are required for construction. Some of the solder pads are pretty small, but the board is high quality and well screened and I found no tendency to create solder bridges. It took a good two hours to fully populate the board.

Plug in connectors are provided for all external connections, which is very convenient. Besides power, you will need a buffered feed from the VFO to be stabilized at a level of 500mV or more, and you will need to connect a compensation varicap into the VFO tuning circuit. I'm hoping to use the existing varicap in the MFJ Cub, but some experimentation may be called for. There is also a tri-colour LED that is used to indicate status.

The board worked the first time it was powered up, with the LED flashing as described in the manual. I then applied some RF using my AA-200 antenna analyzer as the source. The LED indicated that the stabilizer had lock. When I changed the frequency of the antenna analyzer signal, the X-Lock unlocked to allow the frequency to be changed, then locked again a couple of seconds after the frequency was steady.

These days I find circuit construction hard on the eyes, and on the back due to bending over the desk for two or three hours, so I am quite tired after building and testing the X-Lock. Trying it out in the MFJ Cub, and installing it permanently if it does the job, will be a task for another day.