Message-ID: <25511.200101301252@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Tue, 30 Jan 2001 12:56:23 +0000
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Subject: LF: Beacon signals / CW
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Dear LF Group,

I transmitted my usual beacon signal (5 x 110sec dashes and 
spaces, followed by a 400sec space containing 6wpm station ID) 
from about 2000 until 0240 last night, on 135.923kHz. Later, I 
received VA3LK - weakly around 0445, but good copy from 0650 - 
0800, as observed by others. Although in the last week or so 
Larry's signals have probably been strongest at times between 
0000 and 0300, they are more erratic and suffer greater QRN 
during this period. On balance, most consistent copy appears to be 
around dawn here.

Reading through some of the older radio literature, it is apparent 
that the term CW came about to distinguish it from the many other 
types of morse code telegraphy that existed at one time or 
another. Spark transmitters were apparently quite distinctive 
according to how the spark was produced, eg. quenched spark, 
synchronous and asynchronous rotary gaps, etc. The "musical" 
note of the resulting signal seems to have made up to some extent 
for the wide bandwidths, and lack of receiver selectivity. The 
Poulsen Arc transmitter had to use a type of FSK, in order to avoid 
switching the arc off. The only CW transmitters were HF 
alternators.

The early valve transmitters were often anything but CW; rectifiers 
did not come until later, and the transmitter was basically a big 
oscillator fed from whatever DC-ish supply was available. The only 
truly "continuous wave" signals would have been produced by 
battery supplies, but these were the exception. Most transmitters 
seemed to get HT power via some sort of rotating machine, with 
inevitable ripple, or even raw AC, so most of the transmitter signals 
would have been modulated to a greater or lesser extent, in 
frequency as well as amplitude. In those times,  the "T" of an RST 
report would have had more meaning!

Even after well smoothed DC supplies were available, there seems 
to have been operational advantages to having additional 
modulation to the on-off morse keying. So there was modulated 
CW, and interrupted CW. I think MCW of a sort lives on in some 
MF beacons. MCW was also supposed to have advantages on HF 
under selective fading conditions. Also, a non-oscillating detector 
(eg. a crystal) could be used. But I expect some of the older 
subscibers to this reflector know more about this.

The last lot of transatlantic tests in the 1920s saw quite a bit of 
debate about the relative technical merits of new-fangled valve CW 
and trusty dependable spark transmitters. CW won the day that 
time!

Cheers, Jim Moritz
73 de M0BMU