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From: peter@imtec.co.uk (Peter Rushworth)
Newsgroups: sci.electronics
Subject: Re: Does anyone remember the Phantastron tube and how it worked?
Message-ID: <600@imtec.co.uk>
Date: Mon, 10-Aug-87 07:43:08 EDT
Article-I.D.: imtec.600
Posted: Mon Aug 10 07:43:08 1987
Date-Received: Wed, 12-Aug-87 05:02:20 EDT
References: <3574@sdcsvax.UCSD.EDU>
Organization: Imtec Computers Ltd, Peterborough, England
Lines: 19
Summary: TWT's as well


In article <3574@sdcsvax.UCSD.EDU> brian@sdcsvax.UCSD.EDU (Brian Kantor) writes:
>
>It was explained to me that the phantastron tube was basically set up
>so that an electron beam travelled from cathode to anode as in most
>tubes, but that there was a large magnet clamped around the tube to
>force the beam into a helical path to make it longer.  Apparently
>there were a set of electrodes that stretched or compressed the length
>of the helix, thus changing the time it took for the electron beam to
>traverse the tube, thus phase modulating the signal.
>
What you describe sounds similar to what I think is called the "serrodyne"
effect (spelling from memory). I once worked on a system which used
a travelling wave tube to modulate a (GHz) signal like this. I don't recall
magnets, but there was a sawtooth input (<10Khz) to the helix, as you
increased the amplitude, the signal freqency reduced. ( My instructor gave
strict instructions that the helix was never to be disconnected or
the TWT would blow. I subsequently found out that the TWiT's cost
over 1K pounds. :-) )