CW Transmitter w/Superhet Receivers

This circuit evolved from the desire to have transceiver operation when using my homebrew superhet receivers.

The superhet receiver design I use feeds the VFO into the first mixer, which converts the incoming signal to the IF crystal filter frequency.

Going backwards with this design, taking the VFO and mixing it with the IF crystal filter frequency yields the same frequency that is being heard on the receiver.

The circuit that started the design process was "A VXO-Controlled CW Transmitter for 3.5 to 21 MHz", 1988 ARRL Handbook, pp 30-43 to 30-45. It uses a pair of MRF472/MRF476s in the output for about 5 to 6 watts output.

The VXO transmitter uses a VXO as the VFO, which works perfect for using the IF filter crystal feeding into a mixer.

The basic circuit of the VXO transmitter was expanded to include a mixer, with additional filters, buffers and amplifiers as needed to maintain the 5-6 watts output.

One other design criteria was absolutely no pulling of the VFO frequency in the receiver. This made the design a little more complicated, but the results made the additional circuits worthwhile - there is no change in the VFO frequency when transmitting - period!

The circuit values shown in the schematic and pictures are for 20 meter operation, and is currently used with the Super Receiver.

Some additional crystal switching and filters would be needed to obtain the full four band coverage with the Electroluminescent Receiver, and that will be tested and added to this circuit as the work is done.

This circuit is mainly shown at this time for those that want to add transceiver capability to the Electroluminescent Receiver, and have the experience to build the circuits shown "dead bug" style with the modifications needed for the bands you want to cover.

A kit will be designed for the Electroluminescent Receiver with the circuit simplified to bring down the parts count, without compromising performance. The 2N2222 amplifier circuit, as used in the original VXO circuit, will probably be substituted for some of the 2N5109 amps in this design.

W6BKY has a receiver article at Hamradio-online that shows how to build this circuit on a universal printed circuit board. Very compact and includes a diode mixer and crystal filter. Check out http://www.hamradio-online.com//1999/jun/w6bky-16.html

"A VXO-Controlled CW Transmitter for 3.5 to 21 MHz", 1988 ARRL Handbook, pp 30-43 to 30-45.

"A VXO-Controlled CW Transmitter for 3.5 to 21 MHz", 1982 ARRL Handbook, pp 6-34 to 6-36.

The VXO article is probably in all the Handbooks between 1982 to 1988, and maybe beyond. I didn't have any of the 1990's ARRL Handbooks to check.