An Introduction to High Speed CW Meteor Scatter (HSMS) & WSJT


High speed CW has been popular for meteor scatter communication in Europe since the early 70s (and maybe longer). It is now catching on here in North America with somewhat different techniques.. Here's a basic introduction to this mode and WSJT (FSK441).

HSCW: What and Why

When we say high speed CW we are talking about speeds over 200 WPM. We specify the speed in letters per minute, or LPM (WPM = LPM / 5). The lowest speed commonly used is 1000 LPM, but many operators use speeds up to 4000 LPM and even beyond. High speed CW has several advantages over SSB. Most important, it allows usable information to be copied during even the shortest bursts. On SSB, a 1/2 second burst is only enough to copy one letter. On HSCW, complete call signs can be copied in that same burst! Using HSCW, even bursts lasting 1/10 second are useful. This allows contacts to be made at any time of year, without having to wait for a meteor shower. It is also easier to copy weak CW signals than weak SSB signals, making for extended range and again, more contacts. This mode really works for the small stations, too!

How, then?

Obviously, nobody copies those speeds by ear! There are two basic types of techniques and equipment for HSMS work. The older method, still very popular in Europe, involves using modified tape recorders to record incoming bursts and then play them back at a slower speed, in conjunction with high speed memory keyers for transmitting. There are some pitfalls with this system but it has performed extremely well for many years.

The other way to do it is with computers. With a computer and sound card, it is possible to record incoming HSCW and them play it back at a slower speed. It is also possible to generate high speed CW and feed the audio tones into a SSB transmitter as a means of keying. The computerized approach seems to be fuelling the HSMS movement in North America. This technology is still in its infancy and there are not many programs available yet.

The basic technique involves the use of rather long transmitting periods (1 or 2.5 minutes are common) with the receiving station recording any pings or bursts that come in during that time. Then while you are transmitting, you can go back and replay what was heard during the receive sequence at a lower speed. Once you figure out what information was copied, you stop your transmission momentarily and adjust the content accordingly. This means a slight lag between what was heard and your response, but that is not a problem.

There are some problems. Most rigs will not key at these speeds without modification. Some have modified rigs for high speed keying, but most use a keyed audio oscillator and inject the tone into an USB transmitter. This works very well and does not require modifying the rig.

When slowed down for copy, the CW tone can become too low, often less than 100 Hz! A solution to this problem is to use an audio up-converter between the receiver and the tape recorder or sound card when recording. This takes incoming tones and converts them up to 5000 Hz or more. Then when they are played back at slow speed, the tone is "normal".

Where do I get information on software and hardware for this?

Check my Circuits for HSMS page for some schematics of audio osciallators for keying rigs, audio up-converters, etc.

I recommend spending a few moments checking out the following links. These are offered as starting points where you will find information and a lot more links.

LINK K0SM's Home Page. Lots of great info for getting started in HSMS. Andy is doing a great job with the page. Also includes links to software, files to download, etc.

LINK EME, Meteors, much more by W6/PA0ZN! An excellent page with links and info on HSMS. Info on software, hardware. Operating procedures. Info on HSMS mailing list. More.

LINK Make More Miles On VHF European and North American MS scheduling, links to software for MS, more.


WSJT is a new program by Joe, K1JT. It uses an encoding scheme called FSK441 to do high speed meteor scatter operation using a computer. Knowledge of CW is not required. Visit the WSJT Home Page for information and downloads.


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