Super-QRP CW Transmitter

Par / by: Bertrand Zauhar, VE2ZAZ

Do you really believe that with 5 milliwatts you can make a QSO? And How about using a simple computer TTL oscillator as transmitter?!!! Well yes, it is possible! and it works. This transmitter is without doubt the simplest ever built.

The picture above shows the kind of TTL oscillator used in this circuit. It is powered with 5VDC.

Refer to the schematic diagram below.  My circuit is rather simple. You will find oscillator X1. I purchased it in an electronics surplus store. Any amateur frequency can be selected. Mine oscillates at 28.142 MHz. As a matter of fact, the 10 meter band is best for this kind of operation.

In order to ease operation with a shortwave receiver, the proposed circuit includes an antenna transfer relay between the receiver and the transmitter. This relay is energized as soon as the operator depresses the morse key. A release delay is generated by an RC circuit made of C1 and R1. And that is it!

The circuit assembly is not critical. Just keep the wiring as short as possible. You can use a universal perforated board to mount the components.

On the schematic diagram above, positions J1 and J2 will get the coaxial cables for antenna and radio receiver. The preferred coaxial cable for this application is RG-174. It has a small diameter and is more flexible.  J4 will get the 5 VDC supply cable. 

For those of you who can fabricate PCBs, here is my PCB design. It is visible on the figure below. In order to reproduce exactly the PCB, I provide a compressed Postscript (.eps) file. This file can be printed on any postscript laser printer. The resolution obtainable with the postscript file is much better than the figure below.

         Parts List

C1     47uF, electrolytic capacitor
C2     1000pF, ceramic capacitor
D1     1N4148 diode or equiv.
J3      1/8" Stereo jack
K1     5 VDC DPDT miniature relay
Q1     NPN Transistor, TO-92 case
R1     4.7K, 1/4 Watt resistor
X1     TTL oscillator

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