How can I test a sliding termination - also known as a sliding load?

I've got a Maury Microwave sliding load of unknown history which is fitted with an APC-7 connector. Is there any quick tests I can do to see whether the device is basically functional or not? A DVM shows 0 Ohms between the inner and outer conductors, which made no sence to me, as I was expecting a resistance of close to but not exactly 50 Ohms.

I then calibrated a VNA with an *N* caibration kit, added an N to APC-7 adapter, and connected the sliding terminaton to that. Whilst the return loss at low frequencies was really bad, when I set the span of the VNA from 2 GHz to 6 GHz, I see a circle close to the centre of the Smith chart, which is what I would have tought. But the fact the DC resistance is close to zero Ohms is worrying me.

sliding loads are NOT broadband devices. They are certainly not designed to go down to DC. In the older network analyzers, you would use the sliding load in a calibration of higher frequencies (maybe 1 to 18 GHz), and then use a fixed coaxial load for the low frequencies. The combined calibration would cover the whole frequency range.

Sliding Tuners have bandwidth,therefore it's normal to see 0 Ohm at DC.

I know they have a bandwidth and that related to the length, as you can only move the load over some distance, and that needs to be a significant fraction of a wavelength. Hence a 1 MHz sliding load would be a bit big!

But I thought the basic construction was of partically conductive material which slide as one moved the load in and out. That can't explain why I measure a DC resistance of 0.

as i recall, the hp sliding loads had a center rod that had a metal to metal contact with the case at the far end. That is why it appears to have 0 ohms DC. The sliding load material was a hunk of stuff that contacted the center rod, but capacitively contacted the outer coaxial shell. I assume maury is made the same way.

Did HP ever make sliding loads? I know a lot of their cal kits have Maury Microwave sliding loads, so I wonder if they were always made by Maury Microwave, and some have HP badges on them.

Dave

HP made none of that stuff directly, but they did buy it from Maury, alford, omnispectra, etc etc.