The AM Forum

Every year Marconi day is celebrated around the world, how dose it work? All the info I can find dose not explain it very well, you don't use spark-gap transmitters do you. they are not legal.

John W9BFO

You are correct that spark transmitters would not be used, so instead, the spirit of International Marconi Day is celebrated by contacting Marconi event stations using more modern modes such as CW, SSB, FM, AM and available Digital Modes i.e RTTY, PSK31, JT65, and SSTV. The exact mode depends on what the event station you wish to contact is using. This year's event is on April 22.

This website seems to offer the most details:

http://gx4crc.com/imd-award/

I think it was back in the 1970s, but the Marconi Memorial Station on Cape Cod got special permission from the FCC to run an A2-ish transmission in the Amateur CW bands.  They modulated the keyed signal with some sort of harmonic rich audio that was reputed to sound much like a spark transmitter when received with a typical modern narrowband receiver.  But it was less than a kilocycle wide.  I seem to recall that they used the call KM1CC.  I have a QSL somewhere.
I worked them on 80 meters.  It was entertaining to hear fellows giving them RST 599 reports when their signal was not T9.  I think I gave them something like a 593 report.  Perhaps with a head start, the FCC could allow such an emission mode today for bonafide commemorative stations.  It only ran for a short time and didn't hurt anyone, and gave us at least a feel of what it was like to hear an old spark signal.
Years ago, I worked at a TV transmitter with Bob Thompson, the original holder of W1WM, since reassigned in the vanity program.  Bob was a retired shipboard sparks who had indeed run spark transmitters at sea.  Those guys had some stories to tell, and most of them are gone now.  It's fun to remember the technology from whence we have come.

I've been fascinated by the concept behind damped-wave "spark" transmitters (v.s CW) and how they use a spark discharge to trigger a much higher RF oscillation:

(http://w2pa.net/HRH/wp-content/uploads/2012/12/spark-wave-train-300x172.jpg)

By using a disc with several "points" on it rotated at high speed, the spark discharge frequency could be increased within the audible range of several hundred Hz. This effectively created a damped wave modulated by a tone which could be heard more easily than the much grungier sound of a lower rate spark discharge.

W2PA offers an excellent summary on his website:

http://w2pa.net/HRH/spark-radio/ (http://w2pa.net/HRH/spark-radio/)

These stations sent Morse Code. "CW" was sent by stations that used oscillating vacuum tubes that created a Continuous Wave (vs the damped wave of the spark transmitters). The CW stations were much more spectrum efficient although they required a BFO oscillator to be added to receivers. Ops had to switch their receiver modes between Spark and CW!

Bob W2ZM has run a sparker on special occasions !

http://www.w1vd.com/WE2XGR-6spark.html (http://www.w1vd.com/WE2XGR-6spark.html)