I have an antique KC901H. I bought it when it first came out, seduced by what it could do, as a possible alternative to my boat anchor HP140 spectrum analysers ( I have three), complete with all three RF options (!).
Athough I subsequently bought a KC901S as well (which I have just got back into working order; see my other post), the KC901H is still useful as a "loan" machine and a backup.
1) Any firmware updates for it.
2) an Instruction manual, as the control is a bit more awkward than the 901S and trial and error control can be a pain.
As a final thought.....
I no longer need to immediately get a 901v, now I have got my 901S working, but there must be a market for version of the 901V, which only goes to 1 or 1.5ghz, like the 901C, but has a resolution bandwidth in spectrum analyser mode down to 100hz. Then I could dump all my boat anchor spectrum analysers.
I have an HP 141 based analyser, -actually three of them. They take up huge amounts of bench space (so they are on the floor in various rooms) and some time to warm up if you want the tight resolution bandwitdths at higher frequencies. If I am looking with 100hz resolution bandwith with these machines the scan would only be a few tens of Khz at the most, otherwise you got very broad peaks. I have vowed to avoid buying any more boat anchor spectrum analysers and oscilloscopes.
I have located where to tap an output on my old 901h to feed into a small box containing the mixer to feed to a phone audio analyser, but there are many projects waiting which must be done first (machine shop, model steam engines, vintage 1960's computers, several old cars....). Too much to do.....
Must say firstly I have enjoyed following your repair efforts noted on the forum. I have memories of using the old HP141 with all the available modules in my early career. Rather antique now and eventually the persistence tubes die. I tested the KC901S and was very impressed but got the KC901V for its higher top range covering the WiFi bands and agree with you that having 100Hz bandwidth would be nice however there is a catch.
The frequency span that you get with 450 points 100Hz wide is only 45kHz if you don't want to miss anything. Increase the number of sample points to 3400 then the maximum span without gaps is 340kHz. On the plus side you could easily observe Bessel nulls on FM with 100Hz RBW.
Might I suggest you consider getting a HP 70004 mainframe, with modules HP 70904 2.9GHz RF stage, The 300kHz to 10Hz IF section and the HP70900A or preferably B version LO. (you can also swap to the 3MHz to 300kHz IF if you need it that wide. )
It will complement your current KC901S generator capabilities very well.
The big advantage of the KC901, whatever model, is its portability and it is still very useful if you work within its limitations. A laboratory is only good if you can take the RF problem to it!
Thank you for the links to the circuits for the 901h.
They are very useful, in particular the rf schematic.
My thoughts of obtaining a tighter resolution bandwidth by mixing the small frequency band of interest down to audio and then using an audio fft program on a tablet......
The output of the second filter F2 before the AD8307 logarithmic detector could be tapped and brought out to an external connector. A mixer with an appropriate fixed LO frequency could be used as a small dongle input to the tablet running the fft. I think the analyser if frequency is 45mhz.
The analyser sweep is set to pick up the frequency of interest with zero sweep.
Steve Laurence (with a prospect of being able to ditch my boat anchors).