Re: Test input for an SD-32 sampling head


Reginald Beardsley
 

Mark,

Thanks. I have to drive 150 miles round trip to access IEEE papers. I'll be collecting lots of NLTL papers the next time I go to Little Rock.

At the moment I'm working on deriving the equations for a transmission line with impedance steps designed to steepen the leading edge. Purely a passive linear pulse shaper using a coplanar waveguide with an air dielectric with no components if possible. After I have explored that I'll look into the magnitude of the improvement I can get using non-linear elements.

What I have in mind is a coplanar waveguide which starts with a 10 ohm impedance and then in a series of steps rises to 50 ohms. The concept is to apply a phase delay to the low frequencies which is greater than the delay applied to the high frequencies. My biggest concern at the moment is how to make the Q of the low frequency sections low enough to be physically tractable without resorting to coaxial cable.

Each step in impedance produces an infinite impulse response, so the mathematical notation can quickly get out of hand.

I have copied all the stuff from KH4HTV's website and read through most of it. Very nice stuff.

Leo Bodnar uses a Maxim 3949 LED driver in his pulsers. That is specified as 22 ps typical, 36 ps maximum Tr & Tf. That's already quite fast.

A fascinating aspect of this is that the mathematics are closely related to the normal incidence plane wave response of a layered medium in reflection seismology, the design of anti-reflection coatings in optics and to ultra wideband antenna design.


Have Fun!
Reg

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