Author Topic: Keysight DSOX4024A vs Tektronix MDO4024C  (Read 8871 times)

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Online nctnico

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Re: Keysight DSOX4024A vs Tektronix MDO4024C
« Reply #25 on: October 01, 2016, 01:57:13 am »
Never spend what by any standard is a significant amount of money on test gear without having a test drive. After all, at the end of the day *you* and your colleagues have to feel comfortable with the scope and its capabilities.
That is good advice and what also helps is to come up with a real test plan and spend a day going through it to make sure you have covered some ground and have a good feel for the instrument.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline jjoonathan

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Re: Keysight DSOX4024A vs Tektronix MDO4024C
« Reply #26 on: October 04, 2016, 02:52:25 am »
it's pretty much just FFT as on every other scope
Except that they've paid attention to phase noise and spurs, they've broken out power, amplitude/frequency/phase  (including deviation), etc as first class triggerable traces, they store downconverted I/Q data so you can capture time-correlated non-baseband spectra with massive bandwidth / across multiple bands while maintaining temporal resolution. Then you can feed that into signal-vu and perform  wideband demodulation with equalization, time-correlated constellation diagrams, EVM measurements, decodes, and the like.


Quote from: Wuerstchenhund
4Mpts is a sad joke, and depending on what you do this even half or quarters so you might end up with 1Mpts
You keep throwing the "FFT Mpts" figure around even though both myself and that poor R&S engineer you got on the phone earlier have tried to explain why it's not a good tool for talking about Nt!=Nf FFTs. Instead, the relevant quantity is noise floor as a function of time localization and bandwidth. The careful wording in that last bit is a hint at the tradeoffs that are being made.

RTSA: Bad Bandwidth, Good Time Localization, Good Noise Floor
SHSA: Good Bandwidth, Bad Time Localization, Good Noise Floor
MDO: Good Bandwidth, Good Time Localization, Bad Noise Floor

Of course, these are only tradeoffs in the sense of their extrema. If you can live in narrow bands, an RTSA is all you need. If you can live without superb time localization, a swept-het SA is all you need. If you can live without an excellent noise floor, the MDO is all you need. IMO, the MDO sounds like an awfully powerful combination. It has warts and shortcomings in abundance, but there is no good excuse for refusing to even try to tease out the tradeoffs. Pure laziness. Bleh.
 

Online Wuerstchenhund

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Re: Keysight DSOX4024A vs Tektronix MDO4024C
« Reply #27 on: October 04, 2016, 05:44:47 am »
it's pretty much just FFT as on every other scope
Except that they've paid attention to phase noise and spurs, they've broken out power, amplitude/frequency/phase  (including deviation), etc as first class triggerable traces, they store downconverted I/Q data so you can capture time-correlated non-baseband spectra with massive bandwidth / across multiple bands while maintaining temporal resolution. Then you can feed that into signal-vu and perform  wideband demodulation with equalization, time-correlated constellation diagrams, EVM measurements, decodes, and the like.

Yeah, great. Just that I can do pretty much the same (except the 3/6GHz BW) with most other scopes in the price class of the MDO4k (don't forget the naked MDO4104C is already $17k, and the 6Ghz SA option is another $6k).

As to SignalVu, there's similar VSA software from Keysight (VSA 89600A/B) and R&S (VSE), all paid-for as SignalVu. LeCroy has OFDM demodulation and signal analysis options for its normal scope software.

Quote
Quote from: Wuerstchenhund
4Mpts is a sad joke, and depending on what you do this even half or quarters so you might end up with 1Mpts
You keep throwing the "FFT Mpts" figure around even though both myself and that poor R&S engineer you got on the phone earlier have tried to explain why it's not a good tool for talking about Nt!=Nf FFTs.

As already stated, the R&S guy didn't "explain" anything, in fact he was pretty much just parroting what the brochures say - which isn't a lot for a scope for which R&S wants in excess of $10k. He simply couldn't tell me how FFT on the RTO is implemented because he didn't know.

Also, for the way most scopes do FFT (and do so for a reason), the FFT sample size *is* important. The fact that you can use alternative methods to calculate FFTs which don't have the same memory requirements is irrelevant if that's not what your scope does.

Quote
Instead, the relevant quantity is noise floor as a function of time localization and bandwidth. The careful wording in that last bit is a hint at the tradeoffs that are being made.

RTSA: Bad Bandwidth, Good Time Localization, Good Noise Floor
SHSA: Good Bandwidth, Bad Time Localization, Good Noise Floor
MDO: Good Bandwidth, Good Time Localization, Bad Noise Floor

Of course the MDO's "SA" has a good RBW and time localization, but that's pretty much true for any scope with decent FFT. And yes, the noise floor (and the dynamic range) is poor on the MDOs, because they only have an 8bit ADC.

Besides, a RTSA isn't necessarily worse in BW than a Superhet-based SA (swept SA).

Quote
Of course, these are only tradeoffs in the sense of their extrema. If you can live in narrow bands, an RTSA is all you need. If you can live without superb time localization, a swept-het SA is all you need. If you can live without an excellent noise floor, the MDO is all you need. IMO, the MDO sounds like an awfully powerful combination. It has warts and shortcomings in abundance, but there is no good excuse for refusing to even try to tease out the tradeoffs. Pure laziness. Bleh.

Yeah, well, while that is all nice and interesting, it's completely missing the point. Which is that the "SA" in the MDO isn't more than FFT as on any other scope, just coupled with a high BW input. And it's RF performance is nowhere near what you can expect from a decent standalone swept SA. or even a good FFT/Vector SA.
« Last Edit: October 04, 2016, 08:15:50 am by Wuerstchenhund »
 


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