Network Analyzer Query

Do you have a manual? I would suggest reading it or getting it. HP (Agilent) are amassing manuals (service and operation) on-line for their older instruments. If you give the model number, perhaps someone could help you get a PDF copy of the manual.

Normally, the instrument and test fixture(s) are normalized each time you turn the instrument on. Normalization will null phase and amplitude issues. Some HP instruments allow registers to be set for cable length, impedance references, ... The operation manual should have this information.

You should be able to find a specification table for the VNA parts from the supplier or from the Internet. I also assume you really are going for the higher frequencies as the cable length will be critical.

Most VNA's have a calibration or normalisation process. This means it should be possible to compensate for basically any length of cables ( within reason of course!)

The electrical length should not be that critical after you recalibrated your VNA. Make up your cables yourself but be as thorough as possible and look for ready made Belkin rigid or semi-rigid cables.

Cheers

Dan

Okay, thanks Dan (and qrk). Yes, I would like to cover up to the full 1300Mhz if possible so need to be as accurate as I can be.

AFAIA, the interconnects (which is all I'm talking about here - they interface the VNA with the transmission/reflection bridge) can be compensated for electrical length variation from the control panel of the VNA by a couple of centimeters either way; that's all.

Ideally, yes, rigid would be best. In practice, I'm stuck with whatever I can get. I've seen these N-type (coax-feed) plugs on e-bay:

which looked great until I saw the part about "UR43 cable entry." UR43 is a pretty skinny, flossy cable. I know the cables only need to be 2 feet long, however, so I guess that's not worth worrying about? - or is it? Is the cable capacitance figure relevant? Will it give rise to undue phase shift? I'm a bit out of my depth with these finer points. :-(

Paul,

You should be able to get away with very crude cables.

Added capacitances etc. You null them while calibrating. Should not be anything you need to know about!

What kind of VNA is it?

Cheers

Dan

Thanks, Dan. Yeah I know it's practically DC by today's standards, but to me with 150Mhz being the fastest thing I've ever worked on, it's very unfamiliar territory, believe it or not!

It's an old HP 8754A dating back to '79. There's a photo of it here:

I like it because 4-1300Mhz is way enough for me and the thing is totally repairable - no custom chips or SMDs to screw things up and for two hundred quid it was an absolute snip. I basically bought it simply to get a better intuitive understanding of how the properties of lumped and distributed reactances change over frequency and see how components *really* look at higher frequencies. Whilst this doesn't require any absolute degree of accuracy, I'd still like to do all I can to minimise any measurement errors. I might want to measure some active-device S-parameters at some point. Thanks for your input on the subject.

IIRC i actually used one back in the mid 80's. you had to tell the instrument the physical length and it would calibrate and analyze out the rest of the electrical length and residual impedances.