The "Chirpy" 14 parts QRP 10m transceiver video

This is a short video showing "Chirpy" (XBM10-2), my 14 component 28MHz CW transceiver. More details can be found at my website http://sites.google.com/site/g3xbmqrp/Home/xbm10_2.  Best DX is still IT9QAU/QRP but I am hoping for further soon. This is a simple project and, as with all very simple radio projects, it is a compromise between cost, complexity and performance. Nonetheless it DOES work remarkably well for something so simple. AM breakthrough is almost non-existent too, which was a bonus. Couple the audio into a PC rather than a crystal earpiece and  as a bonus you have an SDR receiver capable of copying from about 28.040-28.080kHz. Why the name Chirpy will be evident when you hear the keying!

Chirpy (XBM10-2) improvements

28MHz "Chirpy" Transceiver with tuned antenna match

In the last day I  have made some changes to my ultra-simple CW transceiver for 28MHz. Power output now is around 120mW (was 60mW) and the RX sensitivity about 3-4dB better. Both changes are a result of better matching the tank of the oscillator/mixer to 50 ohms using a tuned circuit with a suitable tap rather than a 100uH choke. At the moment the component count is 14 total (excluding crystal earpiece and key). although this could be reduced to 12 if a suitable single component inductor/capacitor with link winding was substituted for the only tuned circuit. The receiver is working and I copied an SV station and K1TG on 28MHz just now. The TX still chirps though. Now I am looking for some further 2-way QSOs (3 so far with best DX IT9QAU/QRP at 1414kms).

XBM10-2 Micro-transceiver boxed

This afternoon I rebuilt the XBM10-2 28MHz micro-transceiver onto a small piece of copper laminate and put the whole transceiver in a small diecast box. The transceiver still chirps far too much, but it is in a state where more DX contacts will be possible and I can't see an easy way of reducing the chirp without making it more complex. Maybe I should call it the Chirpy-10?  I'm particularly pleased that the TX-RX offset is just perfect for operation on 28.060MHz CW.

I have just realised that by replacing the earpiece with my PC soundcard I can use several SDR packages to allow me to look either side of the QRP calling frequency. This rather defeats the simplicity though!

Getting the shack back

Tomorrow evening my house grows about 200% in size. Actually my 2 delightful young grandchildren and their mums and dads go home meaning I can restore the shack to its main use! At the moment it is a bedroom for the two grandchildren, so amateur operation is impossible. One thing on the agenda is the CQWW SSB contest at the weekend. This is one of the contests I enjoy as it is a good way to work lots of US states and Canadian provinces, even with 5W QRP. Another task is to further optimise the XBM10-2 tiny transceiver, put it in a tiny case and work some more countries with it.

2 countries worked with the 28MHz XBM10-2

Well, off to a good start today with a couple of QSOs with the 2 transistor XBM10-2 60mW 10m CW transceiver. Much to my surprise I got 439 from IT9QAU/QRP at 1547z today.  Distance was 1414km.

Then 599 (with chirp) from M0DRK, who is in the same village as me. So 2 DXCC countries worked already.  On receive, the oscillator will not always start in the latest circuit version in which I've reduced the component count by a further 2 parts (just 11 parts plus crystal and earpiece now).  Still, a very promising start for something so ultra-simple.

UPDATE 1850z 20.11.10: To get the oscillator to always start on RX, to get TX spot-on 28.060 with the right offset for RX I had to revert to the earlier design and put 2 parts back. The revised schematic is shown here. This IS such fun.

2 transistor transceiver for 28MHz CW

This afternoon I built what is probably just about the simplest CW transceiver possible for use on 10m. Based on my XBM80-2 design for 80m, this is essentially the same circuit redone for a 28.060MHz fundamental crystal.

Depending on how much chirp one is prepared to accept (there is quite a bit) the power output is around 50-70mW, which is enough to cross the Atlantic on a good day. With less output the chirp should be reduced. The receiver audio output into the high impedance crystal earpiece is low, but I can hear down to around 2uV (-100dBm) in a quiet room. The circuit is a colpitts oscillator used as a TX oscillator with the key down and as a direct conversion receiver with a single stage oscillator-mixer and separate audio gain stage with the key up.

The rig is full break-in going from RX to TX when the key is pressed. It works as I have already heard Ws on the band today. Broadcast breakthrough does not seem to be an issue. I hope to have a few local QSOs soon, but really believe it will get much further.  It could do with tidying up and boxing and it really needs a small low pass filter for serious use.