Systron-Donner Spectrum Analyzer
Type 809-1 (10MHz - 12.4GHz)

Actually, 809-1 is the designation of the RF section on the right. The manual describes it as a model 762-1. Alternatively it can be referred to as ‘Microwave Spectrum Analyzer type AN/USM-394’ which I believe is its US Military designation.

This piece of hardware has been in my possession since 1985, when my boss at the time said to me “If  you can put the boot of your car between the back door and the skip, I’ll give you a hand with the old analyser”. At the time it was probably 10 or 12 years old and was technically MoD property, having been purchased against a one-time top-secret contract. I first came in contact with it in 1979 when its sole purpose was to monitor 2 signals in the region of 9GHz and to verify that one was sweeping across the other. This task was done inside an anechoic chamber with the lights out because the trace intensity was so poor. By 1985 the test method had been refined and the analyzer consigned to storage since it was MoD property. At the time there was an MoD policy which deemed items of test equipment over 10 years old to be classed as ‘end of life’. The thinking behind this policy was based on the premise that they would become uneconomical to service or repair; thus they were disposed of and/or replaced. It was the belief of many at the time that this old analyser was faulty anyway … the fact that it had to be viewed in a darkened room. With the analyzer safely in my car I then paid a visit to the Calibration Lab to retrieve the service manual and showed the technician the paperwork which proved that the analyzer had been scrapped. Back home and with the help of the manual, I found an internal adjustment that turned up the volts on the CRT and the trace has been nice and bright ever since!

The analyzer came in very handy when I modified an Injection-Locked 9.6GHz oscillator for 10.224GHz. The fact that I had done this at home intrigued my boss who asked how I had managed it. When I told him that I had used the old Systron-Donner analyzer he was even more intrigued since he had assumed that I had stripped it for parts. He was even more surprised to learn that all that had been required to get it into working status was to turn up the HT. I think at that point he may have uttered something about the competence of the Cal-Lab technician.

Then about 2 years ago (2013) I noticed that it was ‘deaf’. I was working on a 10GHz transverter for a friend and discovered that the sensitivity of the analyzer had dropped to the extent that it was unusable. It then gathered dust in my radio room for about a year before being ‘shunted’ out into the hall-way to sit alongside other miscellaneous non-working items. Earlier this week (March 2015), I decided to embark upon a systematic approach to identifying the problem.   

March 2015: