Sunday, August 03, 2008

Building a BITX20 20m SSB transceiver

The current project on the bench is a single sideband transceiver for 14Mhz. It's a kit from Hendricks.


I'm following the instructions and testing as I go rather than one big "smoke" test at the end. So far receive/transmit switching works, the audio amplifier and mic pre-amp and mixer work. Very encouraging.

I first heard about this design on the Soldersmoke podcast. It's by Ashhar Farhan VU2ESE, his article is here.

There is much to commend this circuit, coming out of India it is designed to use low cost easily obtained components. Ashhar comments that if you can't get (or afford) torroid transformer cores, tap washers may be substituted.

amp.gifThe circuit is "bi-directional" in that it uses the narrow crystal filter for both receive and transmit and switches amplifier stages using diode switches. The amplifier stage is pretty much the same throughout so despite the switching it's pretty easy to see how it works.

The kit I'm constructing is revision 3 and has push pull IRF510s in the output so it should deliver about 10 watts which is quite substantial with a reasonable antenna on 20m.

I plan to build this into a box including the frequency counter from Doug N3ZI mentioned earlier.


Construction is going well although I found a few missing and substituted components in the kit.


I'm looking for a signal on 20m to use for receive alignment.

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