CW vs. DW

Let's break out the acronyms today: CW and DW. Unless you are a ham or a radio engineer, these two short acronyms are meaningless. They don't stand for Creative Writing and Data Window. These are continuous wave and damped wave and as you might suspect... they are related.

CW stands for Continuous Wave sometimes written as "continuous waveform."  This describes an electromagnetic wave with both a constant amplitude and a constant frequency.  Rather, that is the text book definition. CW is also the name used to an early form of radio transmission. In CW the carrier wave itself is switched on and off. With this method data is encoded by varied durations of  on and off time intervals. This is a classic implementation of Morse Code.  To further complicate the history of CW these were also called "undamped waves."  Interestingly it has a very modern use as random keyed modulated CW. It is a common source of radio jamming against both radio facsimile and CW transmissions.

DW stands for  damped wave. In DW the amplitude of oscillation decreases over time dropping eventually to zero.  This term also refers to another early method of radio transmission. DW was generated by spark gap transmitters: make/break circuits. These created a series of damped electromagnetic waves. Here information was carried on this signal by telegraphy, turning the transmitter on and off (on-off keying) to send messages in Morse code. Damped waves were the first practical means of radio communication, used during the wireless telegraphy era which ended around 1920. In radio engineering it is now generally referred to as "Class B" emission. However, such transmissions have a wide bandwidth and generate electrical "noise" (electromagnetic interference) which interferes with other radio transmissions.

In nature, amplitude rolls off.  Only in Matlab can we see a hypothetical square wave. So what's the difference again? While CW sounds like it's just perfect Lego™ blocks of RF it's not.  Both waves still have peaks and valleys, but DW has attack and decay. If you look at the two images it's a lot more clear. DW hits and then diminishes like an acoustic wave, CW has more or less equal amplitude until it drops to zero.

The Glory of the CW Keyboard

They just don't make these anymore.  A CW Keyboard was a device which could produce Morse code from a typewriter-like keyboard. Today we have Raspberry Pi and Arduino board kits that can convert the output from a PC or keyer or both. In short, these have long been obsolete... and are rapidly becoming arcane.

The Codetyper above is from the March 1952 issue of CW Amateur Radio Magazine. It was a very early  CW keyboard, it actually predates the term.  For the record, CW stands for "Continious Wave," a term that hearkens back to the very beginnings of radio. The Codetyper was designed by Nathaniel Dorfman and it was written up in CW, Radio and Television News, QST, Radio-Electronics. Even MARS the Army signal Corps Bulletin wrote it up. The Codetyper went for $500 which when corrected for inflation is over $4,000 in today's dollars.

The device broke down the 43 different sequences of dots and dashes into units of time. The dash for example is three units long, and the dot is one. Units were strung in sequence the longest unit of time is the number "0" which is made of 5 dashes in Morse code. Five dashes, at 3 units each is 15 units plus the 4 spaces between them makes 19 units. Everything by definition has to be a subset of that sequence. To accomplish this, the Codetyper had 40 tubes... yes it was tube driven.

But the Codetyper vanished into obscurity by 1953. Hams, even the industrious bunch, were making their own. Catalogs carried kits that subtracted labor costs from complete units like the Codetyper. By the 1960s solid state electronics were widely available and Hams attached pin switches to manual typewriters to bridge the gap. By the 1970s they had integrated circuits, memory and buffers to play with.

With cheaper components in the 70s complete units began appearing on the market again: the Info-Tech M-300, the Picking Keyboard, the HAL MKB-1 and the MFJ-494 Super Keyboard (pictured above.)  The Heathkit HD-8999 came out in the early 1980s, and may have been the last one. MFJ actually still makes a CW Keyboard today: the MFJ-452, but the keyboard is external and connected by a PS/2 port.  There are few if any models on the market today with an integrated keyboard. More here and here.