[CW] Speed vs Bandwidth

[David J. Ring, Jr.]

Gerry,

The speed of the keying is the frequency of the modulation of the carrier.
Morse Telegraphy by on/off keying is a full carrier, double sideband
transmission.

If you take a signal and key it at a rate if 5 dots per second and compare
it with a signal keyed at a rate of 800 dots per second, you would notice a
large change in bandwidth.

An ICW signal which is a CW signal with an interrupter (a "chopper" or
device which keys the r.f. wave) set at 800 times a second will send with a
bandwidth of over 1.5 kHz wide.  If you switch off the chopper, the signal
will be very narrow again.  This is just done with the speed of the keying.

As the frequency of the modulation goes up, the width of the sidebands goes
up.  A 60 wpm signal is keyed at 25 dots/second, a 6 wpm signal is keyed at
2.5 dots/second.  Since the frequency by which the carrier is changed
(modulated) the bandwidth is changed.

On SSB (or AM or FM etc...) bandwidth doesn't increase when you speak
faster, but if you increase the audio frequencies (modulation frequencies)
you will change the bandwidth, just like on CW when you change the
modulation frequency.  However having a wider bandwidth does mean you can
convey more "intelligence" in a second - even if that intelligence is more
fidelity or multiplexing signals.

When you key a CW signal faster, you increase the pulse rate at which the
signal is modulated, thus increasing the bandwidth.  The higher the "Pulse
Repetition Rate" the wider the signal.

But bandwidth on SSB (voice) does go very low when you don't speak!

73

DR
----- Original Message -----
From: "Gerry Maira" <gm@netsync.net>

> There is no difference in bandwidth if the only thing changed is the speed
of keying.
> It's the same as SSB - Talking faster doesn't increase bandwidth.
>
> 73, Gerry KA2MGE