[Icom] IC-756 or an Original Pro

Thu, 19 Dec 2002 19:56:53 -0800

Hi Jim,

As I recall, the transatlantic radiotelephone link used by President
Roosevelt and Prime Minister Churchill during WW2 was ISB with reduced
carrier (-20 dB relative to PEP). The carrier served as an AFC pilot tone
for the receivers. The system used filters similar to those encountered in
telephone multiplex channel modems.

ISB is still widely employed in the Fixed radio services, and for HF
broadcast relays. Two stacked voice channels on the upper sideband, and up
to 10 50b/s RTTY channels on the lower sideband, are a fairly common
configuration.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of res075cz
Sent: Thursday, December 19, 2002 07:46
To: [email protected]
Subject: Re: [Icom] IC-756 or an Original Pro

It is interesting  how things that seem new have been around for so long. In
1955 I was teaching at the Air Force school at Scott Field. At that time I
taught the Western Electric LDT-2 using a technology that was first
developed in the mid thirties. It used double sideband with two voice
transmissions on one sideband and four RTTY signals on the other. The
signals were multiplexed. There was a coil that brought the two sidebands
together while eliminating the carrier but I cannot  for the life of me
think of the name of that coil. The rig used two 4-400 tubes in the final
and was a fun rig to teach and operate.

73 de Jim, K5ROV...