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From QST October 1916: Undamped Wave Transmitters

Posted: 21 Sep 2016 12:18 PM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email


I often scan the column 100, 50, and 25 Years Ago in QST. Its a real
treasure trove of both historical and technical information now that all of
QSTs back issues are now online.

Normally, Id find an article from each of the issues that I think would be
interesting or useful to todays hams and write short reviews of them. This
month, I highlighted several articles, but when I started researching, I
found the first article—an editorial titled Undamped Wave Transmitters—so
fascinating that this blog post will be devoted entirely to this topic.



In the editorial (shown above), QSTs editors ponder how amateurs are going
to make the switch from spark-gapÂ*transmitters and receivers to
undampedÂ*wave transmitters and receivers. In the process of researching
what this really meant, I learned a whole lot about spark gap transmitters
and what the term CW really means.

First, lets take a look at how spark gap transmitters work. I wont go into
detail on that here. There are several good Web pages that describe how
they work: How Spark Transmitters Work ARRL, Spark gap transmitters
Wikipedia, and Spark Tranmitter (Hammond Museum of Radio).

Suffice it to say that spark-gap transmitters produced damped
waves—orÂ*rather a series of damped waves—as shown below. When the spark
fired,



the amplitude would be high and then decrease over time. A series of these
damped waves would make up each dit and dah.

There were several problems with using spark-gap transmitters. One was
that Â*high power was needed to get any range at all, and as we all know,
high power can be dangerous. Another was that the transmissions were very
widebandÂ*and there was really no way for stations to avoid interfering with
one another.

Now, getting back to the editorial. What theyre talking aboutÂ*when they say
undamped waves are continuous waves, or CW. The signal being transmitted
from an undampedÂ*wave transmitter isnt a series of damped waves, but rather
a single continuous wave. From a mathematical point of view, its not really
continuous, that is to say its turned on and off to make ditsÂ*and dahs,Â*but
in comparison to the damped waveform transmission, its certainly a
continuous wave. (Credit to Jacobo Tarrio for explaining this.)

Apparently, the receivers used for receiving undampedÂ*wave transmissions
did not work very well for receiving undamped,Â*or continuous, wave
transmissions. If an amateur decided to convert his station to
undampedÂ*wave transmission, presumably hed also get the appropriate
receiver, and thereafter not be able to communicate with hams that were
still using dampedÂ*wave transmitters and receivers. That kind of sounds
like the changeover from AM to single sideband,Â*doesnt it?

In the end, of course, the better technology won out. UndampedÂ*wave
transmitters caused less interference than damped wave transmitters, and as
noted in the editorial, they were becoming available for a reasonable
price. Im sure this transition ruffled the feathers of the damped-wave
operators, just as the transition to single sideband ruffled the feathers
of the AM operators back in the 1950s.

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