Buying a cheap Spectrum Analyzer?

[Chris55000]

Hi!

I haven't had much need for a Spectrum Analyzer for quite a few years but I realise I'll be needing one when the time comes to repair my Marconi 2018 Generator, as I bought a part–damaged AC13 board cheap that will provide parts to upgrade mine to a 2019!

I am looking at several HP8558B modules (various prices) at the moment, – could Members who are experienced in r.f. give me some advice please if an 8558B isn't suitable?

If any Member has got an S.A. Repair Project (complete but faulty will do fine!) that's not too expensive they're willing to pass on please PM me – I'm looking at 1.5–2 GHz to suit a Marconi 2019!

Chris Williams

[Radio Wrangler]

The 8558 only tuned to 1500MHz.

There is no tuning stabiliser, so drift is a kHz every few seconds, typically.

The early 8590A is also a free running YIG snslyser. `there sre digital controls via DACs, but it can be a bit drifty. You have to get to later 8590 variants before you get stable LOs.

At the Telford rally, there was a stall (an amateur radio club) with a couple of 8591C analysers (the 75 Ohm video/TV optioned variant) going for £300 each These go to 1800MHz.

In general, it's worth finding your way around the different families so you can interpret whatever happens to turn up. This is more likely to be successful than picking a model and looking for one.

There's no substitute for good luck and being in the right time and place

David

[woodchips]

I have an Instek GSP827 not needed.

This was bought some time ago to save having to repair the HP 141 system I have. It is a few years old so digital, and I just can't get on with digital instrument! My TDS420 baffles me on slow sweep speeds, the 7623 works fine, digital, yuk!

It is 2.7GHz, no options, can download the manual off the web.

The problem is that with an analogue analyser there is always the trace across the screen, so it is easy to twiddle knobs to zoom in on the bit of interest. With the digital it just doesn't display anything so have to press buttons to find it then expand. Even the calibrator waveform just doesn't look like it ought to, can't narrow it down to minimum bandwidth. Of course the S/A might be dead, but came from BBC and the other items were ok.

Yours for £200 plus post if you want to gamble.

[Humber888]

The 8557/8558/8559 SA plug-ins were called the economy range by HP. As David says, they do not exhibit the ultimate in stability and also didn't have a tunable selective front end. So they are wide open to all frequencies and you have to be careful about any inputs that might overload the first mixer. I have both an 8558 and 8559 and generally prefer the 8558 so long as it covers the frequencies of interest. Drift is not too bad after warm up, particularly if you don't need the narrowest of bandwidths. There is a tracking generator that will work with the 8558 (8444A ,option 58 or 59 I think). Also the SA plug-ins will go into any 180 series 'scope but often came in a HP182T mainframe which had a longer persistence tube and different outputs on the back.

If you can find one, the 853A mainframe is specifically for these plug-ins and gives you the option of digital storage. So, IMHO, the 8558 is a reasonably cheap purchase for non-demanding tasks and doesn't give you an instant hernia when carried. However, beware the rotary switches where the wipers can fall off and end up at the bottom of the case (if you are lucky). This happens in a number of pieces of HP gear of the era and is repairable but check operation on all ranges before you buy.

[PETERg0rsq]

What do you want to do/measure with the spectrum analyser?

Only real value of a spectrum analyser when testing a signal generater is checking the output to minimise harmonics, therefore you need one that will cover about 10x the output frequency you want to test.

So you will be lookimng at about 10GHz spectrum analyser to be any real use.

A 1.5GHz analyser is only really suitable for testing at HF, or low VHF. They can be useful for peaking local oscillators, and peaking mixer products though, but unless you can see the harmonics could lead you astray!

Unless you are using it to make measurements, then even an old HP spectrum analyser will give enough information to check the output for harmonics, but you will probably spend more time working on the spectrum analysers than the signal generator if looking for a budget 10GHz instrument.!

Personaly, unless you sre going to do this kind of repair often, I wouldnt bother with a spectrum analyser.

Only instrument I could recomend, that fits under £500 and gives 10GHz+ is HP 8569A, but they are getting old and will probably require some work.