Trombones

That trombone looks far from rusty!

There was a microwave phase shifter at the FEL that was a big trombone. Much more massive than those wimpy things. :^)

George H.

John,

Nice.

Have you made it on your own (highland tech) or purchase this elsewhere ? May be a analog model (spice) ?

Habib

I think I got them at flea markets or surplus places, a long time ago. They show up on ebay.

LT Spice has a transmission line model.

Never heard about a trombone in order to tune a delay line ... after all it seems natural. Thank you for the topic John.

Best regards, Habib.

Colby makes programmable delay lines, based on combinations of RF relays and motorized trombones.

Cool pic there.

I need a programmable delay for an upcoming experiment, but I'll probably hack something myself. Those Colby things are expensive.

If you just need a small adjustable delay you might keep an eye out for one of these:

Look for the full kit with the several range jumpers.

I've used them - they work well. Cost something like $12K for the one I got.

There is an expired patent which explains ho Colby's trombones work. Good source of tips on what to be careful of.

Joe Gwinn

There are also extremely high quality trombones / line stretchers in the test sets for old HP network analysers (HP8740A and HP8742A) - before they used computers, the way to do "port extensions" was... to extend the transmission line with a trombone. Since they didn't have computer error correction, they had to be really well made so that the measurements were still accurate and good to 12.5GHz.

These test sets can be had for maybe $50 on e-bay, which is a real bargain. It would be easy enough to take the line stretcher out of one of these (and if desired you could add a stepper motor to make it computer controlled), but it seems wrong to slaughter such a beautifully made instrument for parts.

Chris

Ah, found the discussion about this that I vaguely remembered: