I've got a late model 8410B with option H91. Anyone know what H91 is? It's not mentioned in the manual I have. There are also some custom modifications made at MIT which I suspect were for adapting the old beast for use with a more modern digital sweeper that didn't provide the control signals sent by the old 8620C for multi-octave sweeps. It would help to know what H91 is to sort out the custom stuff from the factory work.
Thanks!
Jon