Dave, Another meter is the Cambridge LOM-510A. I am not sure if it is in your budget but there has been a review made on EEVBlog. There is one currently on eBay with a current amplifier that I have never seen before today. It may be worth reviewing if it meets your needs.
Todd On Mon, Sep 18, 2017 at 12:31 PM, Dr. David Kirkby (Kirkby Microwave Ltd) < drkir...@kirkbymicrowave.co.uk> wrote: > On 18 Sep 2017 00:43, "Charles Steinmetz" <csteinm...@yandex.com> wrote: > > > > > Also, since you said the waveguide is aluminum (and didn't say anything > about plating), be aware that aluminum exposed to air is covered by a thin > aluminum oxide layer (Al2O3), which forms within seconds after a new > surface is exposed. This layer is thin -- generally about 4 nm -- but the > bulk resistivity of Al2O3 is very high, so there is a finite and variable > resistance across the interface between two joined pieces of aluminum > (depending on the area of the joint, the joining pressure, and the extent > to which the joining method produces a clean [oxide-free], gas-tight > interface between the joined surfaces). > > > > Best regards, > > > > Charles > > Thanks. You have confirmed what I was thinking - it is *probably* the > oxide causing the problem. > > It's not a waveguide in the normal sense of the word, transmitting a TE or > TM wave down a hollow tube, but more like a coaxial line transmitting > something close(ish) to a TEM wave. The outer conductor is uncoated > aluminum and rectangular in cross section. The inner conductor is brass. > See pictures attached (I made them small, so quality his not great, but it > should not too use much bandwidth) > > Attached are a couple of pictures, and also S11 measured on a VNA, with one > connector shorted Since this is a reflection measurement, the EM wave > travellels along this twice, so about half the loss would be in each > direction. It is only a rough measurement, but a transmission measurement > showed similar results, but half as much attenuation, as it is only being > attenuated one way. > > Maybe I need to use brass, or silver plate the aluminum. > > The purpose of this was to measure the loss of a very low loss liquid > dielectric, but from discussions I had with someone at NPL, such a > structure is not suitable if the loss is very low. > > Anyway, I have put it an offer on a Keithley microohm meter. I notice there > are a lot of Chinese ones at quite low priced. I've no idea how good/bad > they are. But they are much more modern and cheaper than an *affordable* > Kiethley meter. A Keithley 2002 is well outside my budget. > > Dave > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/volt-nuts > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
