[Boatanchors] Modern AM Modulation techniques

[Rob Atkinson]

All of the AM medium wave broadcast rigs are solid state with class D
RF modules producing various power levels that are stepped on and off
by a streaming binary coded signal derived from an A to D circuit
sampling the program audio.  This is fed to a logic board that steps
on and off needed combinations of RF modules that are paralleled with
each other to provide the needed RF level at any instant.  A 50 KW rig
will have 50 to 100 modules, each using two FETs in power blocks of
500 to maybe 2 KW.  The modules are hot swapable.   Harris can make
rigs up to one or two megawatts by simply building bigger boxes with
more FET modules.
The master mind for this design was now deceased Harris engineer
Hilmer Swanson.  These rigs are about 90% efficient.

here's a brief description of how it works:

http://hawkins.pair.com/wabcnow.shtml#digmodsect

73

Rob
K5UJ

On Mon, Oct 5, 2015 at 10:31 AM, Sheldon Daitch <SDAITCH at bbg.gov> wrote:
> I don't think there is a modern AM MW transmitter in the broadcast world that uses the typical Class B audio modulator with a Class C RF amplifier anymore, well, not many produced in the last 10-15 years or so were built that way.
>
> Most of the modern MW broadcast band transmitters are solid state and even at the higher powers found in HF broadcasting, even with the tube RF amplifiers, many of those transmitters now have solid state modulation sections.
>
> The PEP to carrier power ratio still applies, just the way the transmitters work are different.
>
> 73
> Sheldon
>