At the May 4th Business Meeting, Joe Tavares, KC1BGF, will give a Tech Talk on the “One Transistor Marvel” transceiver. It is a Dave Ingram K4TWJ design that Joe found in a QRP builders book.

The circuit is a one transistor crystal-controlled CW transceiver. The oscillator puts out about 200 mW in the 40-meter band. On receive, a hi-Z crystal earphone across the emitter resistor picks up signals that beats with the oscillator.

This is basically a crystal set with a BFO.

When the code key is pressed, it becomes a transmitter and transmits on 40-meters.

It can be connected to a full size 40 meter antenna. A one or two foot length of wire will work just fine for experimenting.

Shown in the upper right is a pi network you can add to the transceiver.  Its function is to filter out unwanted frequencies.  IJoewill eventually add one to his unit but it will work without it.  Joe needs to find the right toroid to wind the coil for 40 meters.  Joe’s unit is built into an Altoids case.

Joe found that when he connected the earphone, the transmitter won’t work.  He then decoupled the earphone with a 10 uH coil in series with the earphone; and the transmitter started working again.  He figured it would have a high reactance to RF; but it does allow audio to the earphone.  That is the only change he made to the circuit.  Joe hopes his addition doesn’t cause the oscillator to chirp

These are the values for the pi network:

40 m   470pf    16t  #28 wire on T-50-2 toroid
30 m   330pf    13t  #28
20 m  .220pf    12t  #28

 

Joe Tavares, KC1BGF

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