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From: "John Jardine"
Subject: Re: Comb/Harmonic Generators
Date: Thu, 5 Dec 2002 23:35:41 -0000
NNTP-Posting-Date: 5 Dec 2002 23:23:28 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Glen Walpert wrote in message
> In article , "John Jardine"
> >Vance wrote in message
> >> Howdy,
> >> Please forgive the dual post - I'm not familiar with the traffic.
> >> I'm from Picosecond Pulse Labs and we've cobbled together a comb
> >> generator which displays some very interesting characteristics. I'm
> >> making this post for a little market feedback, as we're not systems
> >> designers who use these components.
> >> These devices are not SRD based, so they're not tuned. This means
> >> their input frequency can vary - like 500Mhz to 15Ghz. The harmonic
> >> content is quite strong due to some proprietary technology and we see
> >> more than -10dmb at 40Ghz for a 2Ghz, +10dbm input. The device
> >> consumes about 1.4W.
> >> My questions are these: Are these three characteristics (variable
> >> input, input frequencies to 15Ghz, and significantly higher harmonic
> >> power) of significant value to designers? Are there other
> >> alternatives? Does this enable other trade offs in the design?
> >> Thanks for your feedback.
> >> Vance
> >What's "SRD"
> Step Recovery Diode
> >Otherwise, sounds to me like you've invented a diode ;-)
> No, they have invented a non-linear transmission line edge compressor!
> I saw these advertised in one of the trade rags a while ago, and have been
> trying to figure out how they work ever since. My guess is that they work
> a method analogous to accoustic edge compression - the effective
> constant of the transmission line either decreases with increasing voltage
> (for positive edge compression) or increases (for negative edge
> causing the higher voltage parts of the pulse to travel faster (or slower)
> than lower voltage parts. (In sound propogation the higher pressure part
> the wave travels faster than the lower pressure part, an effect only
> observable at high sound pressures when adiabatic compression causes
> significant heating, usually ignored in basic acoustic primers but very
> important in non-linear acoustics.)
> There is a diode built into these transmission lines, and apparently the
> effective dielectric constant of the transmission changes with the bias of
> diodes? Perhaps Vance could tell us something about these?
> Sorry, I can't think of a good use for them at the moment. Interesting
> devices, though.
Glen, Fascinating stuff, thanks for the links. John's soliton description
seems apt. It's a shame the idea can only be effectively realised by
micro-spaced varactors. This 'preferential addition' process seems very
similar to an idea I saw to break a transmission line into a number of
mis-matched segments. If the calculations were made correctly the forward
pulse edge would steepen as intersegment reflections added cumulatively as
the edge travelled along. sort of like how a tsunami is created.
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