By Brian Justin, WA1ZMS
wa1zms@arrl.net

The early history of wireless contains the names of many great pioneers. While Marconi’s name is the most well known, the names of Fessenden and Heising are only rarely mentioned. As early as 1900, Reginald Fessenden was experimenting with the direct transmission of human speech. During World War I, Raymond Heising was developing a method of constant-current modulation that was one of the earliest forms of AM. Since I have been one of the active CW 600 meter stations as part of the ARRL’s Experimental License project for some time now, I decided to take a step or two further into the realm of early radio transmissions. One of the transmitters I have used for 600 meters CW and QRSS work has been a vintage homebrew design that could support traditional CW and Heising AM. Since the ARRL’s Part 5 license only supports CW and narrow-band digital modes, the Heising modulator went unused until a new idea came to mind.

Fessenden’s early work includes a unique 1906 Christmas Eve transmission of him playing the violin, a recording of Ombra mai fu and a reading of a Bible verse. An idea was thus born to apply for an FCC Special Temporary Authorization (STA) for 600 meter operation that is for amplitude modulation, in particular the Heising modulation. With the cooperation of commercial coastal CW station WNE and the FCC’ Office of Engineering Technology, the STA with call sign WF9XIH was granted for AM transmissions until March 1, 2012 with a center carrier frequency of 472.5 kHz. The plan is to begin a series of evening test transmissions the week of December 18, 2011 with a special recreation of Fessenden’s Christmas Eve transmission at 0200 UTC on December 25 (9 PM EST December 24).

Since it is unlikely that a 5 W AM signal could be heard beyond a few dozen miles, a 500 W solid state linear power amplifier will be used for best DX. WF9XIH is licensed for up to 20 W ERP, just like the WD2XSH stations, and every effort will be made to run as close to that ERP as possible. The same antenna -- a 160m dipole feed as a Marconi-T against ground -- that has been used for WD2XSH/31 will be used for WF9XIH.

Commercial station WNE is currently running CW marine weather transmissions at 0100 and 2200 UTC daily. So you can sharpen your 25 WPM CW skills at those times, too. WF9XIH transmissions are being coordinated with WNE, and any changes to the WNE schedule will alter the WF9XIH operating times. The current plan is to at least make a Heising AM transmission most days at 0200 UTC. Audio loops of speech and a series of stepped audio tones will be used most of the time. The stepped audio tones will make it easier for DX listeners to demodulate in CW or SSB mode, even when they are well beyond the range of the AM signal.

If you copy any of the transmissions, please be sure to log them at www.500kc.com.