Can a SpecAn Tracking Generator be used as an RF signal source?

[jgalak]

I'm planning on buying a less-expensive SpecAn with TG like the Rigol DSA815TG or Siglent SSA3021X (leaning towards the latter).

I've also been needing an RF signal source for various things (mostly in the 100-500MHz range). 

I'm wondering if it's possible to just use the TG from the SpecAn, in some sort of fixed mode.  Would that work?  Or is that not an adequate substitute?

[BillB]

I don't think you can do that with the Siglent SSA3021X.  I believe its TG is automatic and can't be manually adjusted. 

[metrologist]

Maybe in zero span, you can get a pulsing CW signal. It may shut of the SG during retrace blanking. Not sure.

[TheSteve]

Some analyzers do allow the tracking gen to be used as a signal source - often the precise amplitude is not guaranteed though. One option as already mentioned is to set a zero span which will usually get the tracking gen to sit at a fixed frequency. If you then set a really long sweep time the CW source will remain constant with a brief dropout at the end of each sweep. Most of the time you also get a very limited amplitude range and the signal won't be super clean.
Hopefully someone with the Siglent SA you mentioned can comment.

[usagi]

pick up a used R&S cmu200 off ebay, it makes a wonderful RF signal source.

[BillB]

Check out this review from The Signal Path:

https://youtu.be/Fn7uaEVeOPk?t=1541

Starting at about 25 minutes, he discusses and demonstrates using the TG standalone. 

[jgalak]

pick up a used R&S cmu200 off ebay, it makes a wonderful RF signal source.

That seems a bit overkill?  Not really sure what one would do with that.  I don't have any reason to work on GSM, 3G or EDGE communications systems.  Mostly I'm doing amateur radio stuff, voice and digital.  Focusing on APRS right now.  What does something like that accomplish beyond being an RF source?

[usagi]

pick up a used R&S cmu200 off ebay, it makes a wonderful RF signal source.

That seems a bit overkill?  Not really sure what one would do with that.  I don't have any reason to work on GSM, 3G or EDGE communications systems.  Mostly I'm doing amateur radio stuff, voice and digital.  Focusing on APRS right now.  What does something like that accomplish beyond being an RF source?

it's a full blown 10mhz-2.7ghz spectrum analyzer as well. it's extremely high quality, rugged, and can be had very cheaply. it is one of the few spectrum analyzers that can safely tolerate significant power on the input (50W).

it has a very versatile signal generator suitable for RF testing that you would spend lots of $$$ just to get that functionality alone. the spectrum analyzer functionality is just a free bonus.

[Mr. Scram]

I've never seen anyone call it a spec an before. After coming up empty in more than one search engine it finally dawned on me it's an SA.

[usagi]

Used spectrum analyzer buyer's guide - cmu200

[jgalak]

I've never seen anyone call it a spec an before. After coming up empty in more than one search engine it finally dawned on me it's an SA.

No clue where I picked that abbreviation up.  Most likely this forum

[CJay]

CMU200, lovely things, they're really nice sig gens and spectrum analysers and more but beware...

I'd recommend spending the time to do some research and know what you're getting, other than that, go for it, I absolutely love mine.

They are available with a multitude of different hardware modules, none of them detract from the basic spectrum analyser/sig gen function.

However those options can reduce the rating of the input down to 2W maximum or prevent the use of them as a more general purpose radio test set (they can have a *really* nice audio analyser function that can be pressed into service as a general purpose transceiver test function despite being originally intended for cellphones)

They are more difficult to drive than a simple spectrum analyser and the GUI often feels like it's fighting back but once you get to know them a little...

Plus, they're cheap. I got both of mine for a month's disposable pocket money.

[tautech]

Yes.
But with SSA3kX it seems only as a very short sweep.
Screenshots tell all.

[Performa01]

Yes.
But with SSA3kX it seems only as a very short sweep.
Screenshots tell all.

Why not zero span?


I think it has already been stated that the quality of a TG signal usually isn't very good - and for a reason. There is simply no need for anything else than a reasonably accurate frequency and stable amplitude. Harmonic distortion, phase noise, amplitude accuracy and frequency response are rather unimportant for a TG. There are also only few choices for the signal output level and an expensive external step attenuator would be required anyway.

As we have learned from the Signal Path review, the quality happens to be good enough for undemanding tasks, but the TG is still derived from the 1st LO of the spectrum analyzer, so its frequency cannot be set independently. This means that the SA has to be in zero span mode and can only be used as a RF level meter whenever the TG is used as a CW source.

With all these limitations the use of a TG as a replacement for a RF signal generator isn't really attractive.

[jgalak]

Thanks, everyone.  I was fortunate enough to be able to buy several pieces of used test gear, which includes an Elenco SG-9000.  While certainly not the best rf generator ever, it's better than nothing, and should work for most of my immediate needs, at least until I'm able to afford a higher end unit.

[eb4fbz]

Amplitude is usually not calibrated in a TG, and spectral purity is poor as phase noise or spurs doesn't really matters for scalar analysis.