Built the new LARCSet US$39 40m 5W SSB Transceiver from HFSignals

The LARCSet is a 40m 5W SSB Transceiver Kit from hfsignals.com. It's just US$39. The VFO is analog and it's a descendant of the bitx40 line. Ashar Farhan says you can build it in a day and I can cornfirm that promise.

The board comes with the vast majority of components already fitted.

The work that needs to be done by the builder is winding a few toroids (although happly the three trifilar ones come pre-wound), assembling the front panel, fitting potentiometers, soldering crystals and a few transistors including the IRF510. The manual is very clear.

The front panel is held in place by the little screw nuts from the 3.5mm panel mount sockets and I found that there wasn't enough thread on these to hold it in place. I sanded down the front edge of the board and ended up gluing the nuts to better hold it in place.

My VFO toroid needed one extra turn to get it in the right range so bear that in mind when winding.

The varactor tuning is quite sensitive and I think a multi-turn pot or an additional fine tuning pot might be good idea. I like the idea of a totally analog VFO but amusingly QRP-Labs has just announced a compact digital VFO that could be suitable for radios like this. Here's a video showing unboxing, stages of the build, receiver testing and final completion.

I enjoyed the build and it received first go. 

The radio has some rather serious problems. CW produces about 3W but the signal is modulated with a tone. Sideband is extremely weak - it seems that the single transistor microphone amplifier produces vastly too little audio for the mixer. I shorted R73, the feedback resistor in the mic amp, and got a bit more gain.

I found that the bandpass filter, L2 & L3, peaks a bit low - at 6.9Mhz - and I plan to remove a turn to improve sensitivity. Others have pointed out that the output low pass filter is a too aggressive.

Because of the low cost of the kit, shipping is a significant part. HFSignals is offering a pack of five and I'm going to suggest it as a group build project at my local club.

Here's a bit more of it receiving. The VFO is quite stable but tuning is very sensitive. I plan to add a fine tune control.

Here's a better quality rendering of the schematic (click to enlarge):

After following the instructions, rather than the board marking, I've got L4 and L5 in the right spot and now I'm seeing about 2.7W CW out which is a little disappointing but better than before. 

Fine Tune Knob

The main tuning is quite course so I've added a 1K in series with the hot end and this makes tuning much better. Here's a demo:

I've developed a simple 3D printed case which is working quite nicely.

Conclusion

As much as I like this project, I'd have to say I would not recommend version 1. I hope Farhan will work to produce a better revision.