[HCDX]: Re: [AmFmTvDx] Re: tuning the

[Allan and John Dunn <dunn@xxxxxxxxxxxx>]

Sheldon Daitch wrote:

>          New, state of the art high power MW tranmsitters from
>          Harris, do have processors that run things....even my
>          combiner, that takes the power from 5 power blocks, to one
>          output, has a processor, to realign the system when one
>          power block drops and it goes to a mnus 1 situation.  

I am so old that I remember when the way to modulate MW transmitters was
to feed audio from a push-pull vacuum tube stage through a modulation
transformer, the secondary of which is in series with the high voltage
power supply to the final amplifier.  But looking at WABC-770 in New
York City, they use a bunch of combiners of various power levels.  The
audio is digitized into a binary number, and the various bits turn on
and off the combiners in a binary fashion to vary the amplitude of the
carrier to provide modulation.  When no audio is present, it sits at the
50% power level.  When heavily modulated, it varies from near maximum on
for the positive peak to only one tiny bit on during the negative peak. 
It does not shut off completely because that would be in excess of 100%
modulation.  This scenario blows my mind.

Yes, I am also old enough to be proficient with a slide rule.

-Allan-
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