"Stefan Wolfe" ) writes:
"Michael Black" wrote in message
...
"Stefan Wolfe" ) writes:
"Stefan Wolfe" wrote in message
...
You use it to transmit from
your serial port directly to the AM commercial band (10000 Khs) and the
other side listens on a commerical AM radio.
http://sci-toys.com/scitoys/scitoys/...ansmitter.html
Whoops, typo....S/B 1000Khz.


And wouldn't it be A2? Or have they tossed out that designation?

A2 was/is an audio tone into an AM transmitter.

I think in this circuit pin 4 of the serial port connects to the power input
of the oscillator cihip. The oscillator 1MHz "carrier" is truely keyed on
and off, thus it is A1A.


I admit I didn't look at the link before, but having done so, they are
talking about a choice, modulating the oscillator with one of two audio
frequencies, or just on-off keying.

Since they are using one of the control lines of the serial port, rather
than the serial data line, they have full control (well depending on
the operating system) over that line, so they can switch it at a low
rate, for CW, or switch it at a fast rate such as 1KHz, and then doing
that on and off to match the code's on and off.

My expectation that it would be A2 is based on the simple fact that
the average AM radio doesn't have a BFO, and trying to decipher CW without
a BFO is difficult at the very least.

Hence, any project for building a "CW transmitter" in the AM broadcast
band (and the FM broadcast band for that matter, though I don't recall
seeing any of those) would be keying an audio oscillator that modulates
an RF oscillator, so you could hear it in the radio. It's been like
that since 36 years ago when I built one for a science project, and
long before that.

That webpage does acknowledge that you can send straight CW, but
then you'd need a receiver with a BFO, I think they said "expensive
shortwave radio".

Michael VE2BVW