[amsat-bb] Re: DTMF on HF?

[kc6uqh at cox.net]

Howie,
The original Marine selective call used two tones which toggled controlling
a mechanical escapement. At 
the end of each 0-9 digit the hold tone was kept on & a pawl would hold the
escapement wheel if a pin was placed for that number in the wheel. The next
digit would then be dialed. If it was the correct number the escapement
would move around to a fixed contact that would sound a bell. If it was the
wrong digit the wheel would return to the start position. This system was
used on Marine and land mobile phone systems until the SS revolution in the
70's

Art,
KC6UQH



-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Howie DeFelice
Sent: Friday, January 10, 2014 12:18 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] Re: DTMF on HF?

Bob,

I don't have any experience using DTMF on HF but back in the day before
satcom, commercial marine HF SSB coast stations used a dual tone selective
calling system made by Lorain Electronics. The encoder used 11 tones, one
each for the digits 0-9 and a carrier tone. Each digit was transmitted along
with the carrier tone and the difference in frequency was detected to decode
the digit. This compensated for small frequency variations. These worked
very well. You could probably do a similar thing with a single row or column
of DTMF if you didn't need more than 4 digits. 

Howie AB2S 		 	   		  
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