Hi David, and all,
There have been a few 'wet' Amplis.
Big L, probably the most 'pro' of the sixties pirates, had a 'G'. The most
bizarre
was probably the 100kW version on RNI's 'Mebo II', which had two of the mondo
PA tubes per phase; the rectifier stacks apparently weren't up to much so 40kW
was a good day. Of course, there was the 'H' on the Ross. And one on the
Nannell, which never saw light. (Ahem. I wonder which one you knew? Anorak
roulette. . .)
The worst part about them was the phase-modulator itself, which was a 24" rack
wide box full of dozens of tubes and tweaks, with inexorable, continual, alignment
creep evidently being the feature most striven for in its design. Mercifully,
someone came up with a solid-state replacement. On reflection, the same could
be achieved very much more simply nowadays. But it wouldn't use 807s in the
crystal oscillators(!); no fun.
The two carriers were held 135 degrees apart at 'no modulation'; obviously
they swung to in-phase for maximum amplitude and to out-of-phase for
minimum; as to be expected the raw modulation linearity was, well, not very,
but was corrected adequately by copious feedback, detected at the output. I
suspect that a measure of pre-distortion was contrived in the differential
phase-modulator stages, too.
Still, the basic premise of two class-'C's being more efficient than a 'C' plus an
'AB' was a good one.
Even bog-standard plate-modulated senders had a hard time, especially on 558,
where the high Q of the antenna system (which made modulating high audio
frequencies tough enough anyway) persisted in being high Q but definitely
'somewhere else' in frequency as the boat leaned . . . very audible on air,
assuming the thing hadn't ker-chonked in disgust.
Cheers,
Steve W3EEE
1/30/2002 1:04:58 AM, [email protected] wrote:
[email protected] writes:
interestingly, changing the phase to produce amplitude modulation was the
approach RCA followed in the 1960's with their "ampliphase" AM
medium-wave and
short-wave transmitters
I remember it well.
Worked fine on land, and then someone put a 50kW ampliphase transmitter on
a ship in the north sea. They saw some 'interesting' effects as the ship
rolled and the distance from the mast to sea (together with the feed
impedance) changed.
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