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Old 11th Dec 2020, 3:50 am   #1
majoconz
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Default ITC Instruments SA1300B Spectrum Analyser

Hi all - probably not quite vintage but it's reasonably old. I bought this on our local auction website for a pittance - stated as not working properly as the vertical calibration was 1dB out (?) and the frequency display was in error. Well, after a couple of hours investigation into what control did what, I succeeded in getting a trace showing our VHF FM band. However it is quite obvious that the frequency display is not true.
Unfortunately searching for any info comes up with nothing - except in Radio Museum where a different model is shown but nothing other than some very small pix.
The construction is quite novel - it even looks homebrew-ish with all those Eddystone die-cast boxes.
Any info would be gratefully received as this thing show some promise if not quite HP standards - it even has a tracking generator built-in! If I could find the sweep generator it would help. The frequency display is just a straight counter with a 10MHz OXCO on the board.
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Old 11th Dec 2020, 4:32 am   #2
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Default Re: ITC Instruments SA1300B Spectrum Analyser

I think it uses a free-running local oscillator. The 'coarse' and 'fine' tuning controls will be simple pots and the digital centre frequency display will just be a DVM reading the tuning voltage as a rough indicator. So don't expect too much frequency accuracy.

There seems to be no choice of bandwidth, so I guess there's only one, and that's probably not too bad, the range of scan widths from full down to 1MHz/division isn't going to allow you to look into the modulation spectrum of signals other than video ones.

It should be good for looking at band activity and checking for spurious oscillations.

I think it's similar to one of the DIY designs a few radio amateurs have built and published, but prettied up.

It'll teach you a lot about analysers and how to drive basic ones. It's not a full general purpose one, they will go down to kHz wide scans and will have a range of IF bandwidths from perhaps a MHz down to 1kHz in a 1-3-10 sequence. You'll have to navigate in frequency using that marker more than the digital display to have any accuracy in the frequency dimension. If you're lucky it'll be a crystal oscillator for the marker source.

The HP 8558A was their most basic one. Covering 0-1500MHz, it too had open loop tuning from a 10-turn pot with an added fine control pot, and it used a DVM chip to give an rough tuning indication where previous generations had a pointer and string. Bandwidths were 300kHz down to 1kHz though, and there was a lot wider range of sensitivity steps. It still used a YIG tuned oscillator (fairly linear in frequency, but kilodollars expensive) and it drifted about 1kHz per second!

So, the frequency reading being somewhat out is to be expected. It ought to be good for harmonic and spurious checks on transmitters, if you use it with a reasonably good power attenuator, and the tracker ought to let you look at wide-ish filters.

So, for a pittance, I think you've got yourself a good buy. There may not even be anything wrong with it other than just discovering its limitations. It just depends on the magnitude of the errors.

Should give you some fun, but the danger is it'll whet your appetite for a more comprehensive one.

David (One of the designers of some of the HP ones, many years ago)
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Old 11th Dec 2020, 6:21 am   #3
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Default Re: ITC Instruments SA1300B Spectrum Analyser

Mid 90's, 1.3GHz, made by Advance Instruments in the US (now out of business).

Apparently there is only one manual that covers all their range which also has the schematics, if you can find one.

The front panel looks familiar in that it "may" have been from a commercial 'scope, possibly Gould (with a new overlay), with the 'spectrum' bit added - possibly based on a TV Tuner front-end.
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Old 11th Dec 2020, 7:39 pm   #4
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Default Re: ITC Instruments SA1300B Spectrum Analyser

You might find this of interest an advert from 73 magazine published Aug 1994. It gives few pointers to the specification and options.
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Old 11th Dec 2020, 8:16 pm   #5
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Default Re: ITC Instruments SA1300B Spectrum Analyser

Thanks everybody for the info. The advert in 73 magazine makes it look really good - but that's what ads are supposed to do! That pic is of an "A" model which looks slightly different. A search for more info turned up blank, but I'll delve a bit deeper. The guy I bought it from thought there might be a power supply defect but with no specs and nothing printed on the board it's going to be tricky.
Thanks all.
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Old 12th Dec 2020, 12:13 am   #6
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Default Re: ITC Instruments SA1300B Spectrum Analyser

The internal picture shows a proper commercial pcb assembly for the scope section and, as you say, a somewhat amateurish implementation for the rest.

Have a look on the scope pcb for any discernable numbers that might lead to the identity of it and possible info/schematics for that part.
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Old 11th Jan 2021, 2:10 am   #7
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Default Re: ITC Instruments SA1300B Spectrum Analyser

Terry VK5TM sent me a private message saying that he recalled Jeff Wallach N5ITU had the service note for this SA but this was some time ago. I sent a message via the ARRL email service and Jeff kindly came back to me saying that the info was probably lost in a hard drive crash, but if he could find the backup he would get back to me. A couple of weeks later I had an email from Jeff with attached documentation which was of great help but unfortunately didn't go quite deep enough into the service notes, more like an operator's setup. Never mind, thanks to Jeff and to Terry for their good work - any time I can return the favour, don't hesitate.
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Old 11th Jan 2021, 2:21 am   #8
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Default Re: ITC Instruments SA1300B Spectrum Analyser

Two things have shown themselves - the boards behind the frequency display are a frequency counter which I can make to count -25Hz right up to 1.3GHz. Immediately behind that is an input attenuator which should be fed fro the buttons on the front panel but I actually suspect those buttons control the logarithmic attenuator. Behind that on top which had me baffled until I found a circuit diagram that matched the components and so I deduced it was a sawtooth generator. There's three potentiometers on there - the diagram says they are sweep width, amplitude and linearity. Twiddling one at a time (so that I could return them to their original position) affects the frequency display - but now I need to find the oscillator that it's sweeping. There's a 555 timer on that board which probably resets the sweep rate so I'm hoping if I stop the timer I might get one fixed frequency, I suspect at the start or the end of a sweep. We'll see!
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Old 11th Jan 2021, 2:57 am   #9
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Default Re: ITC Instruments SA1300B Spectrum Analyser

If there's a frequency counter showing the centre frequency, then it will have to pause in the centre long enough for the counter to run. Maybe it stops mid-sweep, or maybe it runs an uninterrupted sweep, goes to the centre and runs the counter in the retrace blanking period.

With a simple prescaler in the counter, the gate time will be that factor greater than the reciprocal of the frequency resolution.

The other question is whether it counts the actual LO and computes the first IF offset, or does the counter work from the tracking generator? If the latter, those tracking generator controls will affect the counter result.

David
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