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
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