Systron-Donner Spectrum Analyzer
Type 809-1 (10MHz - 12.4GHz), page 6

With the analyzer working again I have to admit that I’m of the opinion that it is now performing better than before. The photograph on the right shows two signals in the region of 7MHz as received on my Inverted-V connected directly to the analyzer input; no external amplifier. Also, when this photograph was taken, the mast was down at half-height because of gale-force winds. So the average height of the antenna would be around 3m. In the past I had only been able to see signals like this with an external wide-band amplifier at the analyzer input. Note that this is also below 10MHz; the analyzer’s specified lower limit. There is a drop-off in performance at the lower end of it’s frequency coverage but only about 6dB. Previously the drop-off was dramatic, with sensitivity below 100MHz being about 20dB down on that at 1GHz. I replaced the faulty GPD-462 with a GPD-405. Both are spec’d at 13dB gain. I measured the gain of the GPD-405 as 14dB. As previously said, the GPD-405 is a more robust device, capable of delivering a higher level of signal with greatly improved noise figure. However these enhancements would not produce the perceived performance improvement. Thus I have to conclude that the 260MHz amplifier had been faulty for some time and only failed completely two years ago.

Why the need for a Spectrum Analyzer anyway? Used correctly, a spectrum analyzer can show the user the exact spectral output of a transmitter, amplifier or oscillator. Even sophisticated power meters, like my HP 436A are broad-band and do not distinguish between wanted and unwanted signal content. Connecting a badly tuned oscillator/multiplier to a power meter might give an indication of 10mW, but half of that or more might be unwanted harmonics and spurii. This is where the RF spectrum Analyzer excels. It allows the user, at a glance, to check if unwanted signal content is present. I don’t know what the rules are these days, but back in 1976 when I applied for my Amateur Radio licence there was a section on the form where I had to list what equipment (including model number and serial number, if known)  I intended to use to ensure that my transmitter was not likely to interfere with other services. Because of where I worked at the time, I was able to list quite a lot of RF test equipment including a Hewlett-Packard HP8558B spectrum analyzer, which I remember drifted very badly. In the 1930s it was a different story. The following is a quote from Wireless Transmission for Radio Amateurs published in 1938 …

‘Applicants must satisfy the Postmaster General as to their qualification and intention to conduct experiments of scientific value or public utility. If scientific investigation is intended they should be certified as competent investigators by a Government Department or some recognized scientific body. Authority to use wireless sending apparatus, even with an artificial aerial can be granted only if the nature of the proposed experiments and other circumstances warrant that course.’

Basically, one had to demonstrate the proposed experiments to a representative from the Post Office. … How times change!

Download the Service Manual

Systron-Donner became part of Thorn-EMI, possibly as long ago as 1980. Consequently replacement parts and manuals are hard to come by. So when I began writing this piece, I envisaged that it would only be a matter of time before someone asked for a copy of the manual. So I have made it available for download. It is a copy of a copy so the quality is not brilliant.  The sections that are scored out are my doing (30 yrs ago) and refer to the -2 version. The files are large so I would suggest ‘right-clicking’ then ‘saving as’.

                             Operation and Service manual: PDF of 121 pages, 50MB                            

                                    Schematics and ‘pull-outs’: Zip file of 25 Jpegs, 6MB

                                                               Items List: PDF of 79 pages, 26MB

Please DO NOT re-sell this manual