I often scan the column “100, 50, and 25 Years Ago” in QST. It’s a real treasure trove of both historical and technical information now that all of QST’s back issues are now online.
Normally, I’d find an article from each of the issues that I think would be interesting or useful to today’s 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), QST’s editors ponder how amateurs are going to make the switch from spark-gap transmitters and receivers to undamped 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, let’s take a look at how spark gap transmitters work. I won’t 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—or 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 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 wideband and there was really no way for stations to avoid interfering with one another.
Now, getting back to the editorial. What they’re talking about when they say “undamped waves” are continuous waves, or CW. The signal being transmitted from an undamped wave transmitter isn’t a series of damped waves, but rather a single continuous wave. From a mathematical point of view, it’s not really continuous, that is to say it’s turned on and off to make dits and dahs, but in comparison to the damped waveform transmission, it’s certainly a continuous wave. (Credit to Jacobo Tarrio for explaining this.)
Apparently, the receivers used for receiving undamped wave transmissions did not work very well for receiving undamped, or continuous, wave transmissions. If an amateur decided to convert his station to undamped wave transmission, presumably he’d also get the appropriate receiver, and thereafter not be able to communicate with hams that were still using damped wave transmitters and receivers. That kind of sounds like the changeover from AM to single sideband, doesn’t it?
In the end, of course, the better technology won out. Undamped wave transmitters caused less interference than damped wave transmitters, and as noted in the editorial, they were becoming available for a reasonable price. I’m 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.
Leave a Reply