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Date: Wed, 30 Jan 2002 22:08:27 -0500
To: rsgb_lf_group@blacksheep.org
From: "Steve Dove" <dsp@hifidelity.com>
Subject: Re: LF: Ampliphase
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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, G0MRF@aol.com wrote:

>   andre.kesteloot@ieee.org 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. 
>
>