Products > Test Equipment
Two Tone Test with Scope and SA
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SilverSolder:

--- Quote from: mawyatt on August 03, 2020, 02:14:05 am ---
--- Quote from: SilverSolder on August 03, 2020, 12:07:00 am ---Just for fun, here is what the tone test looked like in 1975!

I fired up an ancient HP 3571A Spectrum Analyzer -  a 100% analog spectrum analyzer full of gold, crystal filters, and engineering love. 

The two tones are generated by HP3325A x2 summed into a 50 ohm load.

The analog output from the 3571A was tracked on the scope in roll mode for display.

It seems to me the performance is not embarrassing at all, considering this thing is 45 years old.  The noise floor is a bit high, but the 3325A signal generators are not exactly low noise...   The 3571A is capable of -130dB, perhaps a little better, performance on a clean signal.  The ancients knew how to build stuff!  (It probably didn't cost $450)


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Those old instruments can still hold their own :-+

Brings back fond memories, along with the superb Tek analog scopes of that era :)

Best,

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Sometimes I just buy weird stuff on eBay because it looks interesting and doesn't cost much.  It gives the same feeling as starting an old muscle car and taking it for a drive - giving a hard time to the occasional new car!  :D

I have managed to avoid going down the Tek scope rabbit hole, even though I can see the admirable engineering that is going on with them.   There is only so much space in the man cave!   ;D
tautech:

--- Quote from: jemangedeslolos on August 03, 2020, 02:55:15 pm ---I made some quick tests on my MSO7014. source is a Siglent SDG2082X  :

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In Dot mode ?  :-//
jemangedeslolos:

--- Quote from: tautech on August 03, 2020, 07:09:12 pm ---
--- Quote from: jemangedeslolos on August 03, 2020, 02:55:15 pm ---I made some quick tests on my MSO7014. source is a Siglent SDG2082X  :

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In Dot mode ?  :-//

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No, vector mode on channel 1 but color grading option enabled in FFT settings.
I left the memory depth management in auto.
I hid the channel on most on my screenshot but I can redo the measurements without hiding the channels and without activating color grading option.
In the end, the results are the same.
We miss max hold on FFT settings in Rigol scope so I can't replicate your screenshots.
tautech:

--- Quote from: jemangedeslolos on August 03, 2020, 07:26:46 pm ---
--- Quote from: tautech on August 03, 2020, 07:09:12 pm ---
--- Quote from: jemangedeslolos on August 03, 2020, 02:55:15 pm ---I made some quick tests on my MSO7014. source is a Siglent SDG2082X  :

--- End quote ---
In Dot mode ?  :-//

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No, vector mode on channel 1 but color grading option enabled in FFT settings.
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:o
Then why is there just dots below the 2 highest markers ?  :-//


--- Quote ---We miss max hold on FFT settings in Rigol scope so I can't replicate your screenshots.
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Can you engage any averaging ?
Enough and it cleans up FFT much like Peak hold albeit at a lower value.
rf-loop:
This whole two tone test can be just fun playing or it can be serious tests for analyze equipment.
Separate peoples do separate tests with different settings and ... all different. So results are some times just nonsense and or not at all comparable.
First need do some definitions and this also depends what are we testing. if there is under testing oscilloscope front end it is really not 10kHz thing.  After then also signal level is more than important. After then signal source is very important. Example two tones need really be well isolated from each others ... and list continue... endless untiol peoples do some deal and define test parameters what all use. Other way... like old sentence. Garbage in - garbage out.

Different oscilloscopes have different analog front end. Input levels are divided to some bands and inside bands some small steps.
One perhaps important thing is try first find where is front end 1dB compression point. Why. Because more linearity less mixing. So different scopes may be tested with very different front end working point related to its best linearity. Result may be totally different if test same scope with different level. 
So, it need define what is right level for two tone tests so that it is any kind of useful and comparaple or is it better to keep just for fun playing. And now one question is, is it same power.... ups voltage level for different scopes. Or is it same proportional level from one V/div setting full scale.
I am thousands of km far from my test equipments so I can not demonstrate how important this is specify so that results are comparable and give some real useful information.

Used test level.
Two tones sources isolation. Is it isolated when one function generator digitally combine two tones - really.
Oscilloscope BW is mostly least 100MHz. Often 200... 300.... 500 etc etc. Testing with 10kHz and then compare scopes is like fun joke.

Last time I characterize one noname SA using two tone test I have two fully separate identical high quality RF generators and well isolating combine with test lab grade components. Even if I need test only up to 100MHz I have not even think to use function generator what can internally "somehow" combine two carriers if I do not want just keeping some fun.  Yes they can combine and this is suitable and ok for many kind of purposes but imho fully questionable for serious IP3 tests.

https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_application/application_notes/1ma71/1MA71_2e_amplifier_nonlin_meas.pdf

Specially chapter 3 beginning and then there bit later 3.4.

Of course now SA used is now inside DUT, oscilloscope.
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