I've got a customer that wants to build a low power monopulse radar sensor. I've told them they need to buy some equipment. I think at a minimum they need a network analyzer for testing antennas and a fast scope for poking around in their prototype circuits. They only have $20k to spend and this includes needed fittings and active probes. They're talking around about 200 ps rise times. Any suggestions for equipment? Can anyone suggest a favorite used equipment vendor that offers warranties?
Not a used equipment vendor, but using highly-available parts...
Tom McEwan's patents have schematics for his various radars, including the SRD-based ones which have rise times like that. He even lists preferred vendors for some parts. I'm looking forward to having time to play in that space myself.
Wait a minute ... for a project like this you're going to need people that know how to do it. Those people will know what equipment they need. It just seems screwy that somebody wants to do a project and doesn't know what equipment will be needed.
Ebay Tektronics 11801 scope and a sampling head. The SD22 head is good, low noise and 14 GHz. But the SD24 head does TDR, which means it basically has a built-in 30 ps pulse generator. I've seen a signal from one SD24 channel into the other, through a pair of wideband antennas.
There is a probe head for the 11801, the SD14, 3 GHz at the tip.
If you're working wideband, you could stay in time domain and avoid the VNA.
That gear is relatively cheap, a few per cent of what new stuff would cost.
The 11801 is overkill for 200 ps, but a good deal anyhow.
John Larkin Highland Technology, Inc
picosecond timing precision measurement
200 ps isn't hard--you can do that on a dead-bug proto.
Starting with an 11801-series scope is a good idea--you can get one for
1-2k at the moment. I'd want to spend another $3k for a TDS 694C, if possible, because sampling scopes like the 1180x are a bit frustrating if you don't know when exactly your signal is going to arrive.
For the OP: The reason is that all the input circuitry of a sampling scope is hidden behind the sampling bridge, so whatever happens between samples is invisible to it. That means that you can't trigger a sampling scope from its signal inputs, the way you do with an ordinary scope.
Jim Williams points out that that makes samplers just the ticket for measuring the settling transients of fast amplifiers. They're also good for an amazing number of other things, if you can get the trigger pulse from somewhere.
The TDS 694C has about 125 ps rise time, 10 Gs/s simultaneously on all four channels. It's an amazing amount of bang for the buck.
Oh, one other suggestion: an HP 70820A Microwave Transition Analyzer, about $800. I have no idea what moron gave it its name, but the gizmo itself is astounding. It's a sampler-based, 40-GHz vector network analyzer / spectrum analyzer / dual channel oscilloscope.
It's a wonderful piece of gear for the sort of job under discussion, and very very cheap because nobody knows what it does!
Yes, we are. Don't forget you can also *hire* network analyzers which might be a better idea than lashing out BIG DOUGH on an outright purchase. Last time I looked there was some guy on Ebay hiring VNAs and a all sorts of other high-end test equipment from the best manufacturers: Agilent, LeCroy n' shit. :)