The mention of controlled carrier modulation brought back memories of my
DX-40 transmitter. However, controlled carrier modulation was used long
before WW II. The 1936 Radio Handbook had a number of transmitters using
controlled carrier, and some of the methods used have been almost forgotten.
One method mentioned was grid controlled mercury vapor rectifiers. This was
especially recommended for use in 3 phase power systems, because of the lag
reduction because of the smaller value filter caps.
Another method was "variactor" control, which uses the saturation of a
voltage-dropping reactor in series with the primary of the Class C amplifier
plate supply.
One of the advantages of the controlled carrier exciter was that it could be
used with a class B linear amplifier. With the reduction in carrier while
not talking, the plate dissipation requirements for the class B amplifier
was reduced. There were no 3CX3000 tubes available surplus in 1936.
There is an article on how to assemble and adjust the variactor core, if you
like to roll your own.
Colin K7FM
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