HP 803A VHF Bridge Impedance And Angle

[oz2cpu]

any one know this one ?
very impressive unit

any ideas why my output level is a bit low ?
like 20-30dB too low

see all details here
https://youtu.be/oHWhDqUBWrM

[jwet]

Wow- that is a beautiful instrument.  I graduated in EE in 1982 and we had things like this in my RF course (EE353 at Illinois).  I remember using General Radio wheatstone bridges at lower frequencies that worked with buik L's and C's.  At higher frequencies, there were slotted lines used up to a gigahertz. This is basically a slotted line that is bent into a circle.  Not much can go wrong.  I can only imagine the contact to the slotted line (the wiper) is dirty but I don't think even that is a problem.  They are not lossless at all- the -40 db min insertion loss is a minimum and with a matched load, it could be well below 80db- this is your return loss and a very good match is -50 or more meaning your detector output would be 90 db below your input.  I think its essentially working.  In the old days, you would use bridges with a radio receiver- they can easily have a sensitivity down to -120 db narrow band.  This is way before spectrum analyzers.  This is the predecessor of the VNA- imagine those little $50 VNA's do what this does.  Button it and use it- its working.  In the corner of my all university lab, there was a brand new 8505 Network Analyzer that displayed Smith charts with little acetate overlays for the scales.  After you spent the semester doing all this stuff, they would show you the VNA and you'd be amazed.  I think its working!

[oz2cpu]

thanks a lot for your time and comment,
I read the manual about insertion loss, that is why i dare to ask about the values i see,
there is no way the resistors or couplings can be damaged, so it must simply be an error in the manual ?
back then, sensitivity was an issue, maybe they used a much more powerfull signal generator ?