[Milsurplus] Re: mechanical modulator ... definitely not a wobulator

[Mike Morrow]

>So, this would have been in the category of an experiment,
>right? I mean, unless this was also a secret, there don't seem
>to have been US submarines generally with TTY equipment
>onboard.

I also have reservations about the concept of the USN using an AM broadcast station to transmit radioteletype (RATT) to WWII submarines, other than as an experimental episode.

To my knowledge, WWII US submarines carried no RATT gear.  US submarine operations were primarily in the far-Pacific, which would make a Florida station somewhat misplaced.  WWII submarines spent most of their sea time on the surface, so HF communications circuits would have been available and easily used.

The physical security that would be appropriate for such a shore-based installation and attendant personnel and equipment would deserve note.

One presumes that the AM station's carrier frequency would have been frequency shift keyed between the nominal carrier frequency and an offset at least 0.5 kHz away.  Since there are usually regions on the fringe of an AM broadcast station's coverage where a competing station on the same frequency may also be heard, a keyed 500 Hz beat note between the RATT carrier and the carrier of the other station on the frequency should have been easily observable in such regions.   

US submarine communications was a concern of mine as an officer on a ballistic missile boat, thirty years ago.  Our main communication receivers were AN/BRR-3 (14 to 30 kHz) sets, and one broader-coverage AN/WRR-3 (14 to 600 kHz) set.  Our goal was to maintain 100 percent copy, 100 percent of the time, of the applicable channels **while submerged** on patrol, using one of several antenna types.  The processing equipment made the radio room something like a computer center.  Unlike other submarines, all our patrol time was spent submerged, and VLF (or lower) frequencies were required to make the trip to us.  The communication channels available to a surfaced WWII submarine were much broader, even if more primitive.

With respect to my original post, I did not say that FM modulation of a MF signal was impossible (remember 160m ham NBFM from 50 years ago?).  I only said that a wobulator wouldn't be a very good device to cause it.

Mike / KK5F