19 Oct 2011

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.

5 comments:

Anonymous said...

Hi Roger

That design is so simple and easy to build. Thanks again for another future project. BTW with an overtone crystal oscillator could this idea work for six and four meters.
A simple CW transmitter with your NE602 converter would be a quick way of getting on Four meters.

Tony

Anonymous said...

Never tried a simple one transistor transceiver on four meters.

Tony

Roger said...

The amount of chirp on TX is really too excessive on 10m so going any higher would be pushing it Tony. I am still trying to think of other ways of making this rig simpler still!

David said...

Even simpler?

A car ignition coil and a very narrow bandpass filter ? :-)

73

David - G7UVW

Anonymous said...

Roger

Did you see this Months PW Carrying On The Practical Way The Rev. George Dobbs G3RJV presents two very simple receivers one a FET regen and the other using the mixing technique for your 28 MHz CW transceiver.

Tony