Bolstering the Beacon

Having received pleasing reports for the 30m beacon, it was time to consolidate a loose affiliation of components on a breadboard into something a bit more permanent. I also fell victim to the dreaded "specification creep" and decided to make some "improvements"...

First, I wanted to improve stability of the VXO, so I added a regulated power supply to the oscillator stage. At the same time, I realized it would be easy to kludge together a "power down" option for the VXO - no need to have it pumping out a signal (particularly one in the 80m band) when the beacon is running in WSPR mode.

Here's the revised VXO, which certainly doesn't deserve to win any prizes for circuit design - yet has the attractive property of working rather well!


The 2n3906 implements the brute force power-down and the two stages before it are about level conversion from the ~12V circuitry to an active high (5V) control line for the PIC.

The beloved EAGLE produced a pcb design, which was quickly translated into copper. Drilling the myriad holes in a pcb like this is by far the most tedious part of the process...

... perhaps I'll get into surface mount!

Anyway, to cut a long story short, a new PCB takes the stand-alone beacon idea one step closer to reality - here's the VXO in detail...


and here's the balanced mixer - I hope you like the technicolor tri-filar windings on the toroid...


The whole system, seen below plugged into the band-pass filter and Si570 USB Synth (Radio Times amp and LP filter are off to the right) does indeed offer the sought-after improvement in frequency stability on-air...


The loop-back seen at the bottom right corner of the board is where I will have option to switch in the "IF" signals associated with my DSB WSPR Station when I get around to it - all I need is a 2 pole change-over switch; one pole to select the appropriate IF signal and one to signal to the PIC to power down the VXO (when in WSPR mode). I've retained the in-circuit programming interface (at top left) so I can plug in the PicKit2 programmer/debugger and make software changes.

Notice how useful blobs of Blu-Tack are in stopping wayward circuit boards skating all over the bench.

Next steps include...

• remembering how to power up the USB Synth locally (so I can completely sever the funiculus umbilicalis from the PC)
• putting the whole shooting match in a box of some kind
• setting up a dedicated beacon antenna to free up the main station g5rv

...-.- de m0xpd