QCX assembly Rev 1.08
115
The simple key-shaping circuit used here
uses only a few components but produces
good results.
This circuit was derived by one published by
Don Huff W6JL, see
https://www.qrz.com/db/W6JL/
though as he
says, “
this integrator-type keying circuit is
found in many published homebrew designs
over the past 40 years or so, so it is nothing
new
”. It uses a PNP transistor (Q6) and R-C
integrator circuit. Don W6JL uses this key-
shaping circuit to drive a 600W Power
Amplifier.
On key down the Q4 switch is “closed” by a high signal coming from the microcontroller. In a really
simple transmitter, Q4 could just be replaced by a straight Morse key to ground! But in our case,
the microcontroller implements automated stored message sending, beacon modes, and Iambic
keyer
– so we need the microcontroller to be the boss of everything. The microcontroller reads the
state of the straight key or paddle, and processes it to produce a key output. When in straight key
mode the microcontroller transfers the signal straight through from the key input, to the key output
control line
– but in other modes the processor must generate the keying signal.
The component values set the rise and fall time. With the components shown, the rise and fall time
is about 5 milliseconds.
The following oscilloscope screenshots show a 40m band (7MHz) transmission, keyed with a
continuous series of CW dits at approximately 24 words per minute. The amplitude is
approximately 3.8W into a 50-ohm dummy load (with 12V power supply).
Summary of Contents for QCX 5W CW
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