A simple VOX interface for WSPR.
Having recently acquired an FT-817 I was interested in trying it in WSPR mode. It didn’t take much research to discover that the DATA connector on the rear panel has bi-directional audio, labelled as data. PTT is also available on the same connector. Unfortunately there is no VOX capability when using this port.
I already had a couple of USB soundcards ( $5 on eBay ) so I decided to utilise one of them as an audio interface to the USB port on the laptop. I removed the USB plug and replaced it with a socket. A standard USB to USB connects the interface to my laptop. The audio jacks were also removed and the mini DIN was wired directly to the exposed pads.
Since the soundcard can produce a few volts of audio during transmit, I decided to use a simple voltage doubler to convert some of the audio signal to DC for the transistor switched PTT control. The audio is delivered directly to the voltage doubler, but is potted down for the transmit drive to the radio. A series resistor also helps protect the mic input of the soundcard. You should set the mode to DIG.
To my surprise, the whole thing worked first time and spots from Australia and USA were reported during the first 500mW transmit cycle. WSPR really is an amazing mode. The most difficult part was getting it in the box, neatly !
The box is the smallest from Jaycar. Shown without the lid. The braid simply bonds all the ground points with a low impedance path.
Took a little time to get the layout ‘safe’, so that none of the parts touched.
No box. Maybe some heatshrink tubing.
My favourite construction method, with NO GLUE !
I am forever tinkering with circuits of one kind or another. Usually receivers. Etching a PCB for a one off project is too time consuming and hardly cost effective. On the other hand, strip-board is not the best medium for RF construction. I am also not a fan of “ugly construction”. So for many years I manually cut squares and oblongs onto my PCB’s using a craft knife and a steel straight edge. Then I discovered ‘Me Squares’ and ‘Me Pads’. My first few project using these pads took up more space than I had bargained for as the pads were spaced out to accommodate the components. Also it was a bit messy getting just that tiny amount of super glue on the pad. Then one day I accidentally knocked over a half full bottle of glue. It was difficult to put things down for a while !
Later, while building a classic post mixer amplifier, I drew the pad layout on squared paper. The individual pads were just a few mm apart. I quickly realized that if I stood some of the resistors upright I would not need to separate the pads at all. A little further planning and I had the whole circuit module on pads, in one piece. I recommend spending a little time on this, as the result is well worth the effort. Just follow the schematic layout from left to right. Try to get at least one grounded component on each side of your module.
This example uses the 8 pin audio amplifier the LM380-8. Here is the schematic.
Here is the module built on pads and squares.
Here is the same module mounted on the PCB. There are usually sufficient components going to ground that NO GLUE is needed to hold the module down to the copper substrate.
The grounded components are holding everything in place. I’m sure there will be the odd occasion when a pad will need to be glued down. For me this is a last resort, and I now use double sided adhesive tape if really needed.
Most of the projects posted here are constructed in this way. You should try it, it really works well, and it undeniably look good.
73 from ZL4SAE