(click for a larger version, 200kbytes)
This transmitter was built using mosly components from the junk box, so the values shown are not mandatory. The oscillator is based on a 14000 kHz XTAL which by chance resonates on about 14002 kHz, then divided by-2 with a JK flip-flop to obtain the signal on 40m.
The power amplifier stage consists of 4 line drivers in parallel (4 out of 8 available on the 74HC240), always keyed. Frequency shift is obtained with the 1N4007 diode in reverse polarization in a sort of "on-off" fashion provided by the NE555 and the extra buffer stage.
You may achieve CW keying by controlling pin 1 of 74HC240, that is the /OE (active on low level) control.
You may remove the squarewave generator at all to obtain a single frequency signal.
You may keep 1N4007 and 220pF cap and substitute 100kOhm+1kOhm resistors with a 100kOhm trimpot to control transmitter's frequency to some extent.
Reception reports measured the frequency being 7001.19 kHz. A sample screenshot:
Since I am not an expert of 40m propagation, these reception reports teach me that it is possible to cover a 600-700 km hop during sunlight and after sunset for a couple of hours. 100mW TX power probably mean 25 milliWatt ERP in my antenna setup.