Can a SpecAn Tracking Generator be used as an RF signal source? - Page 1
Forum section: electronics / testgear

author: jgalak
author_rank: Regular Contributor
timestamp: April 04, 2018, 05:56:37 pm
content: 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?

author: BillB
author_rank: Unknown
timestamp: April 04, 2018, 05:59:03 pm
content: I don't think you can do that with the Siglent SSA3021X. I believe its TG is automatic and can't be manually adjusted.

author: metrologist
author_rank: Super Contributor
timestamp: April 04, 2018, 06:36:49 pm
content: Maybe in zero span, you can get a pulsing CW signal. It may shut of the SG during retrace blanking. Not sure.

author: TheSteve
author_rank: Unknown
timestamp: April 04, 2018, 06:50:28 pm
content: 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.

author: usagi
author_rank: Frequent Contributor
timestamp: April 04, 2018, 07:09:33 pm
content: pick up a used R&S cmu200 off ebay, it makes a wonderful RF signal source.

author: BillB
author_rank: Unknown
timestamp: April 04, 2018, 09:06:14 pm
content: Check out this review from The Signal Path:https://youtu.be/Fn7uaEVeOPk?t=1541Starting at about 25 minutes, he discusses and demonstrates using the TG standalone.

author: jgalak
author_rank: Regular Contributor
timestamp: April 05, 2018, 02:27:05 am
content: Quote from: usagi on April 04, 2018, 07:09:33 pmThat 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?

author: usagi
author_rank: Frequent Contributor
timestamp: April 07, 2018, 03:50:48 am
content: Quote from: jgalak on April 05, 2018, 02:27:05 amit'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.

author: Mr. Scram
author_rank: Super Contributor
timestamp: April 07, 2018, 04:00:08 am
content: 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.

author: usagi
author_rank: Frequent Contributor
timestamp: April 07, 2018, 04:19:54 am
content: Used spectrum analyzer buyer's guide - cmu200

author: jgalak
author_rank: Regular Contributor
timestamp: April 07, 2018, 05:44:33 am
content: Quote from: Mr. Scram on April 07, 2018, 04:00:08 amNo clue where I picked that abbreviation up. Most likely this forum

author: CJay
author_rank: Super Contributor
timestamp: April 07, 2018, 06:34:44 am
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: April 07, 2018, 09:53:44 am
content: Yes.But with SSA3kX it seems only as a very short sweep.Screenshots tell all.

author: Performa01
author_rank: Super Contributor
timestamp: April 08, 2018, 08:54:46 am
content: Quote from: tautech on April 07, 2018, 09:53:44 amWhy 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.

author: jgalak
author_rank: Regular Contributor
timestamp: April 08, 2018, 01:00:03 pm
content: 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.

author: eb4fbz
author_rank: Regular Contributor
timestamp: April 08, 2018, 01:01:56 pm
content: 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.