Siglent SDS1x04X-E BodePlot II (SFRA) features and testings

[pope]

Apologies if this has already been discussed but I can't find any information.

I would like to do the following and I don't know whether it's possible.

I would like to combine/add two signals (eg. on inputs 1 & 2) with the polarity inverted on one input (eg. on input 3) and do a bode plot of the combined signal. Is this possible with the 1104x-e?

Thanks!

In short, no.

It's a shame. Is any other scope able to do this?

[2N3055]

I don't think any will let you do Bode plot over Math channel. At least not ones I know off..

[pope]

I don't think any will let you do Bode plot over Math channel. At least not ones I know off..

Interesting. I wonder why... thanks for the answer anyway 

[luciof]

I made some tests with an SDS 1104X-E  6.1.37R9 (ext. to 200MHz) and an SDG 2042 X (ext. to 120 MHz).
Bode Plot II works very well within the audio range and more. For higher frequencies, impedance matched fixtures would work best, but this is not always possible and - anyway - better suited instruments would be needed for trustful measurements.

For practical purposes, I think that the supplied PP510 10x probes are fine up to a few tens MHz; better yet, low capacitance active probes would be ideal to minimize DUT loading.

First test: 10x probes on CH1 and CH2 directly clamped to the generator output.

This worked better than expected (to me), usable up to 65 MHz within +/-1 dB.

But, there's a problem.
CH1 and CH2 use the same ADC, and - as expected - there's no appreciabile skew.
The same setup with CH1 and CH3 (each on its own ADC) gives the following plots:

Here the phase begins to visibly change beyond 1+ MHz, due to a delay between CH1 and CH3. From the data table, we read -12.8 deg. @ 39.81 MHz, which corresponds to 12.8/360*1000/39.81 = 0.893 ns (CH1 is delayed with respect to CH3).
After setting up an 890 ps deskew [not sure about the sign] on CH3, this is the new run:

There is [almost] no change from previous plots, meaning that channel deskew is ignored by Bode Plot (or maybe I missed something).
Anyway, almost 1 full ns of skew between channels should never happen, so I attached the probes to the output of a 40 ps risetime L.Bodnar square wave generator to see what happens:

This confirms that CH1 is delayed with respect to CH3, but only by about 100 ps - not easy to evaluate.

Conclusion: Bode Plot II is a very handy and usable feature, but for a proficient use of the phase plot beyond a few MHz, it should be allowed to enter a delay parameter to each scope channel for manual compensation (automatic phase compensation at selected frequencies after a preliminary a test run would be great).

As a side note, the input attenuation (1x, 10x etc.) should be properly set before entering the Bode Plot environment. I see that this setting is quite cumbersome:
1) select the desired channel
2) press button #4 "Probe nnX"
3) press button #1 "Probe nnX"
4) select attenuation using the Adjust knob
5) carefully press the knob without changing the selection
The most used attenuation factors are 1x and 10x by far, so it would be nice to alternate 1x and 10x by repeatedly pressing button #4. This way, selecting 1x or 10x would be much much faster.

That's all... Thanks to anyone who has had the patience to read this stuff 

[tautech]

I made some tests with an SDS 1104X-E  6.1.37R9 (ext. to 200MHz) and an SDG 2042 X (ext. to 120 MHz).

But, there's a problem.
CH1 and CH2 use the same ADC, and - as expected - there's no appreciabile skew.

You would be well advised to study this and following posts to see some ways Skew can be much reduced:
https://www.eevblog.com/forum/testgear/siglent-sds1x04x-e-bodeplot-ii-(sfra)-features-and-testing-(coming)/msg4045984/#msg4045984

[luciof]

Thanks tautech;
I had already read the whole topic before, and specifically the post you pointed out. I also realize that I haven't made it entirely clear what I meant.

To be clear, I'm quite happy with the scope; I'm not criticizing it, but trying to point out some details to improve it further.

Regarding the skew and the related phase plot derating:

1- In my very basic setup, there is no significant skew related to cables and connections; in fact, using a single generator output and two "ADC coupled" scope channels (CH1 & CH2 or CH3 & CH4) the phase plot looks quite good (actually, the plots go haywire beyond 60 MHz, but this is because I clamped both the probe clips to a stub of wire stuck into the generator output and both ground clips clamped to the BNC ground shell. In previous tests with impedance-matched cables, terminations etc. this didn't happen, but anyway the plots were quite the same below 50 MHz, and it's enough for this evaluation).
2- The main issue arises using unrelated channels ( (CH1 or CH2) & (CH3 or CH4) ). In this case I consistently find a phase derating due to a constant delay between the scope channels; in my tests, the calculated delay is around 850-900 ps.
3- At first, one would think it's the skew between the scope channels, but it is unrealistically large and - in fact - the real skew is far smaller (about 100 ps or less, difficult to measure properly and usually negligible). Moreover, setting a deskew on the scope channels seems to make no difference
4- Anyway, in real measurement setups some significant time mismatch is always possible, and it would be very handy to be allowed to enter a compensation (delay value) parameter in Bode Plot II settings
5- In fact, when using two coupled generator outputs for bode plotting (as suggested somewhere to avoid power splitting fixtures), in previous impedance matched tests I found that the generator outputs were quite well matched in both frequency and amplitude, but there was a delay of about 280 ps between them. The only way to practically compensate this, I think, would be a specific compensation parameter (i.e., the delay parameter of point (4)).
6- Finally, I think that this kind of issue is usually underestimated because the main plot is the amplitude (modulo) plot, and often phase plot is discarded after a quick look; neverthless, in more involved works it can be very useful.


That's all for now. Sorry for the numbered layout above: it helped me to better explain my points while struggling to write in English..., and thanks again for your attention.

[Performa01]

Yes, the limited accuracy of phase measurements between the two separate ADCs have been discovered a long time ago, as can be demonstrated by the attached old screenshots from June 2019:

SDS1104X-E_Y-t_Phase_Error

SDS1104X-E_FRA_Phase_Error

These demonstrate how four signals with phase differences of no more than 3.15° in the time domain can be measured as up to 40° in the Bode Plot. Since it is quite obvious that this is a channel skew issue, the fact that the channel Deskew parameter is ignored by the Bode Plot has been discovered back then as well and I’m surprised that we never got a fix.

Maybe there are some restrictions in the HW architecture that prevent an easy solution.

In any case, this does not make the Bode Plot useless, even at high frequencies.

Just restrict measurements to a single ADC whenever you need accurate phase information at frequencies beyond a couple MHz. You lose the ability to plot three channels in parallel, but then again, we should never forget that competing products are limited to a single channel up to 25 MHz or so, hence a single channel up to 120 MHz should still be a major advantage. And there’s still the option of having three channels, even when phase information gets inaccurate above a couple MHz.

Maybe sometimes we just can’t get everything in the cheapest package; at least for the more advanced HW-platforms, Siglent have addressed these issues. Reply #3585 in the SDS2000X Plus thread demonstrates just this:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4370986/#msg4370986

I’m not keen on the idea of introducing a specific correction parameter in the Bode Plot. We want a correlation between time domain and frequency domain (at least in the higher class instruments we can watch the time domain during bode plot), so just using the Deskew parameter that is already there would be the obvious solution. I suspect this is the reason for the phase error in the SDS1004X-E in the first place; the normal y-t operation always needs some compensation for runtime differences anyway – and there it works. If Bode Plot would use these corrected data, there wouldn’t be any problems. For some reason it seems to use the uncorrected RAW data instead.

I’ll try to clarify this.

[luciof]

Yes, the limited accuracy of phase measurements between the two separate ADCs have been discovered a long time ago, as can be demonstrated by the attached old screenshots from June 2019:

SDS1104X-E_Y-t_Phase_Error

SDS1104X-E_FRA_Phase_Error

These demonstrate how four signals with phase differences of no more than 3.15° in the time domain can be measured as up to 40° in the Bode Plot. Since it is quite obvious that this is a channel skew issue, the fact that the channel Deskew parameter is ignored by the Bode Plot has been discovered back then as well and I’m surprised that we never got a fix.

The actual skew we see (3.15° @ 100 MHz) boils down to 97 ps, while the [more or less] 32° @ 100 MHz we see in the plot are about 890 ps, so the "time domain delay" and "bode plot delay" are definitely distinct; moreover, even if I change the deskew, the phase plots don't change anyway.

In any case, this does not make the Bode Plot useless, even at high frequencies.

Just restrict measurements to a single ADC whenever you need accurate phase information at frequencies beyond a couple MHz. You lose the ability to plot three channels in parallel, but then again, we should never forget that competing products are limited to a single channel up to 25 MHz or so, hence a single channel up to 120 MHz should still be a major advantage. And there’s still the option of having three channels, even when phase information gets inaccurate above a couple MHz.

Maybe sometimes we just can’t get everything in the cheapest package; at least for the more advanced HW-platforms, Siglent have addressed these issues. Reply #3585 in the SDS2000X Plus thread demonstrates just this:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4370986/#msg4370986

I agree, the system is very well usable within its limits, but I don't see this scope as a "cheap" one, rather a "low cost, high performance/cost ratio instrument". I think this should translate to the [reasonably] best exploitation of its hardware combined with a well honed UI. While this is still a cost, I would see it more as an investment, because a degree of sloppiness in a $500 device might be also expected in a $5000 one from the same firm [of course this is not  the case, just to make the point ]

I’m not keen on the idea of introducing a specific correction parameter in the Bode Plot. We want a correlation between time domain and frequency domain (at least in the higher class instruments we can watch the time domain during bode plot), so just using the Deskew parameter that is already there would be the obvious solution. I suspect this is the reason for the phase error in the SDS1004X-E in the first place; the normal y-t operation always needs some compensation for runtime differences anyway – and there it works. If Bode Plot would use these corrected data, there wouldn’t be any problems. For some reason it seems to use the uncorrected RAW data instead.

Here I don't agree.
Ideally, we would sample both input and output of the DUT in the exact same instant; this is obviously not possible, but if this timing error is reasonably constant, we can take it into account very easily when doing the math. For sure, this delay is not part of the results we need and - if well carachterized - can and should be cancelled out.
Concluding (and reiterating):
First, it's true that only in very rare occasions more than 2 channels are needed, and even then, when accurate and reliable plots beyond - say - 10 MHz are required, they'll need very accurate setups and probably something more than a generic scope and generator. But why give up something the hardware is well capable of doing, with only minor firmware adjustments? (And anyway, I see the abnormal and unmodifiable skew in bode plot more as a bug than a missing feature; if the skew was the actual one we see in time domain it might be good enough without compensation).
Second, a "delay" parameter in the Bode Plot environment would take care very well of the issue we are talking of, and allow to compensate for non-instrument related delays. Two examples come to mind:
1) I have the following setup:
generator --> 50 ohm cable --> DUT (with 50 ohm input and output Z) --> 50 ohm cable --> 50 ohm pass-thru terminator --> scope BNC
the output channel is OK; now I need to also connect the DUT input to the scope; below - say - 100 MHz, I think the best way is to clip an active probe (only 1-2 pF loading) to the DUT input. But now we'll have a "large" delay (>5 ns for sure) which would make the phase plot practically unusable
2) Using an SDG2000X generator with coupled channels to make my connections simpler (one output to the DUT input, the other one to the scope input channel. In my case this adds up a further delay of about 300 ps (see picture)

In both examples, a simple user parameter would cleanly solve the problem.

To me, this is a fine instrument, and not "for its price", but I would better say "within its class and specifications". And I think it could be improved further with minor refinements.

[rf-loop]

Yes, the limited accuracy of phase measurements between the two separate ADCs have been discovered a long time ago, as can be demonstrated by the attached old screenshots from June 2019:

SDS1104X-E_Y-t_Phase_Error

SDS1104X-E_FRA_Phase_Error

These demonstrate how four signals with phase differences of no more than 3.15° in the time domain can be measured as up to 40° in the Bode Plot. Since it is quite obvious that this is a channel skew issue, the fact that the channel Deskew parameter is ignored by the Bode Plot has been discovered back then as well and I’m surprised that we never got a fix.

Maybe there are some restrictions in the HW architecture that prevent an easy solution.

In any case, this does not make the Bode Plot useless, even at high frequencies.

Just restrict measurements to a single ADC whenever you need accurate phase information at frequencies beyond a couple MHz. You lose the ability to plot three channels in parallel, but then again, we should never forget that competing products are limited to a single channel up to 25 MHz or so, hence a single channel up to 120 MHz should still be a major advantage. And there’s still the option of having three channels, even when phase information gets inaccurate above a couple MHz.

Maybe sometimes we just can’t get everything in the cheapest package; at least for the more advanced HW-platforms, Siglent have addressed these issues. Reply #3585 in the SDS2000X Plus thread demonstrates just this:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4370986/#msg4370986

I’m not keen on the idea of introducing a specific correction parameter in the Bode Plot. We want a correlation between time domain and frequency domain (at least in the higher class instruments we can watch the time domain during bode plot), so just using the Deskew parameter that is already there would be the obvious solution. I suspect this is the reason for the phase error in the SDS1004X-E in the first place; the normal y-t operation always needs some compensation for runtime differences anyway – and there it works. If Bode Plot would use these corrected data, there wouldn’t be any problems. For some reason it seems to use the uncorrected RAW data instead.

I’ll try to clarify this.

Channels Skev adjustment works also in FRA (least in my old SDS1004X-E) but way Ch Skew adjust works is really poor.
Have not tested now enough, but when I found my old handwritten piece of paper ("post it") note. I tried it just but due to other things very busy only very limitedly and quikly(=error warning!).

My SDS FW is 6.1.37R8

Looks somehow (when FRA in use) that it is still so that  when ADC's are interleaved (true ADC speed 1GSa/s) Skev adjust resolution is 1ns and when ADC's non interleaved mode (true ADC speed 500MSa/s) resolution is 2ns! what resolutions are really enormously too rough when we work higher frequencies (example over 1MHz. @1MHz  1ns responds 0.36 degree and @60MHz 21.6 degree what also was masured result here - naturally because time shift IS 1ns in this case.).
It need remember what are sample intervals. This is only true time resolution! There is nothing below 1ns resolution (except fine intepolation between true raw samples)


In quick and "dirty" test I use 1-60MHz sweep.
FRA:
Source generator Ch1. This was splitted with matched cable pair to oscilloscope ref CH1 and "dut out" CH3
If CH1 and CH3 alone active and all CH Settings all zero.  Maximum phase error around 0.4 degree
If I adjust then CH3 Skew nothing happen until Skev is 1ns. With this Skew result is roughly +22 degree error.

But then FRA settings all same (just Ch1 and Ch3 etc):
Oscilloscope all 4 channels in use. (2 and 4 not FRA use)
Now ADC's work at 500MSa/s (I do not here talk anything about decimated samplerates, it do not matter here)
CH's Skew all 0.   Result at 60MHz.  Phase error roughly -22 degree.

Okay, then I think I adjust Ch3 Skew. I set it to 1.0ns   Result: nothing happen, FRA displayed same roughly -22 degree phase at 60MHz.

Next I set Ch3 Skew to 2.0ns. 
Result:  Phase error at 60MHz is now roughly +22 degree.

I can assume that if I can set Skev to 1.0ns it is quite same as originally when only two channels are in use and 1GSa/s
But now 1ns set is ignored (it really looks like resolution is 2ns  (sample interval without fine interpolation)

When Skew only works every 1ns or 2ns, it's like a 22" spanner on a watchmaker's workbench.
Of course if one do only 1kHz or 10kHz things... it is different case.

Why there is this 1ns shift between ADC's interleaved and non interleaved mode. Even if Skew can not work with fine interpolation in FRA,  still this 1ns  BUG between ADC's interleaved/non interleaved mode is imho BUG.
 
Naturally it can compensate example using 1ns delay. Example ~20cm RG223.
Set of fixed delay lines is always good to have (adjustable delays/phase shifters even better - and expensive).


It is bit surprise this BUG is still there! 
.... somehow as if old jobs are left unfinished when you jump into a new job and think "time to take care of problems". Time doesn't take care of them. These unfinished jobs still have to be taken care of fully, and that requires doing the right thing, not just pretending. After all, bosses often want their workers hands to wave a lot, but they forget that quality is more important than quantity. Insufficient quality, however, sometimes later pulls the rug from under your feet.

[mawyatt]

Not knowing exactly how the instrument takes the sample and in what order if in interleave or sequential mode, so this is just a "What if" statement.

If the samples of "Input" and "Output" are interchanged in time sequence for a single averaged "Sample Point" on the Bode Plot it seems the time skew would be removed in the averaging for a single Sample Point. Think the Bode Plot does use multiple samples to render a final Sample Point to improve Sample Point fidelity, so alternately swapping actual In/Out sample time sequence then averaging seems reasonable.

Best,

[Performa01]

Channels Skev adjustment works also in FRA (least in my old SDS1004X-E) but way Ch Skew adjust works is really poor.
Have not tested now enough, but when I found my old handwritten piece of paper ("post it") note. I tried it just but due to other things very busy only very limitedly and quikly(=error warning!).

My SDS FW is 6.1.37R8

Looks somehow (when FRA in use) that it is still so that  when ADC's are interleaved (true ADC speed 1GSa/s) Skev adjust resolution is 1ns and when ADC's non interleaved mode (true ADC speed 500MSa/s) resolution is 2ns! what resolutions are really enormously too rough when we work higher frequencies (example over 1MHz. @1MHz  1ns responds 0.36 degree and @60MHz 21.6 degree what also was masured result here - naturally because time shift IS 1ns in this case.).
It need remember what are sample intervals. This is only true time resolution! There is nothing below 1ns resolution (except fine intepolation between true raw samples)

Okay, this makes sense now.

Of course, both the normal DSO operation (y-t) and the Bode Plot use the raw sample data as basis.

The y-t display uses the deskew parameter to fine positipon the trace with regard to the trigger point. The resolution for this can be as fine as we like - it's just a "graphical" operation.

Bode Plot could do the very same. Instead of positioning a trace in a graph window, it would have to add the Deskew time to the phase measurement. Really simple.

[rf-loop]

...it would have to add the Deskew time to the phase measurement. Really simple.

And because this is so simple it is totally amazing it is not already done. SDS1004X-E was Siglent first model where FRA was launched. And still this channels Skew is missing and now we live year 2022.

But then, my opinion is that it is perhaps better if we don not use oscilloscope channels Skew parameter at all in FRA, let these be scope (xt) alone.
I like if FRA have its own channels time correction adjustments (FRA channels Skew (perhaps oscilloscope channels Skew ignored)
I have couple of strong arguments for that, which I will not present in this envinronment now. I'm just saying simply that the FRA of all models needs to be develop better in terms of a few functions and UI for better usabiolity and for performance.

But naturally "first aid" simple solution is: just  correct FRA phase calculus with oscilloscope user adjusted Skew (using set parameter full resolution)


Different other thing, BUG (in SDS1004X-E ) is that there is this 1ns time error related to 2 separate ADC's. This is not based to different signal travel time. It is some kind of ADC data stream handling bug in FRA.  Also this can ask why this bug is still there.

[gf]

1) I have the following setup:
generator --> 50 ohm cable --> DUT (with 50 ohm input and output Z) --> 50 ohm cable --> 50 ohm pass-thru terminator --> scope BNC
the output channel is OK; now I need to also connect the DUT input to the scope; below - say - 100 MHz, I think the best way is to clip an active probe (only 1-2 pF loading) to the DUT input.

Active probe is likely overkill here, since the loading at the DUT input does not matter. Whatever voltage appears at the probe tip, it is always the input voltage of the DUT, and the Bode plot is the ratio between output and input voltage. So the Bode plot appears as if the DUT were driven by an ideal voltage source. OTOH, loading at the DUT output does matter if the DUT's output impedance is not zero.

[luciof]

Yes, you're right, I overdid it. In this case (even at the 120 MHz max frequency) a regular 10x passive probe would be enough, rather taking care to not create ground loops or other disturbances (which would be true for any kind of probing)..

[mawyatt]

Different other thing, BUG (in SDS1004X-E ) is that there is this 1ns time error related to 2 separate ADC's. This is not based to different signal travel time. It is some kind of ADC data stream handling bug in FRA.  Also this can ask why this bug is still there.

If this is a time limitation in the FPGA, swapping the ADCs between which is first to acquire and last to acquire, then averaging the readings seems at it would eliminate this time limitation and render a average reading of the ADC samples.

Best,

[Warpspeed]

Bode plots of passive filters and broadband amplifiers is not that difficult because the signals being measured are going to be fairly clean. 
Its just a case of having sufficient available dynamic range, and a nice low noise floor.

The situation changes pretty dramatically when trying to characterize the feedback loop in a very noisy switching power supply. This is not an uncommon application these days, in fact for many power electronics designers, it would be the ONLY application equipment like this would ever be used for.

Can anyone demonstrate resolving millivolt and sub millivolt signals in the presence of perhaps volts of extremely fast rise time noise spikes and broad band hash?
Will it do it ?
Can it do it ?

[FunJumper]

Hi Guy.

Can the Bode II setup be saved from within the Bode II application on SDS1104x-e? I only see a save data in csv. How can the Bode II setup be saved to external USB?

Thanks.
FunJumper

[tautech]

Hi Guy.

Can the Bode II setup be saved from within the Bode II application on SDS1104x-e? I only see a save data in csv. How can the Bode II setup be saved to external USB?

Thanks.
FunJumper

With latest firmware Bode plot settings are autosaved and returned from last use.

There is no way to save explicitly the Bode plot settings although using the Save/Recall Setup to USB should also capture Bode plot settings.

[jeraymond]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

[pope]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

Did you figure it out? I'm also not sure what the "Arbitrary dB" is.

On a different note, is there any way of choosing which trace you want to be visible? It seems to me that both the gain and the phase traces are always visible. AFAIK the sds2000x plus has this option but what about the SDS1x04X-E ? Is this feature missing?

[jeraymond]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

Did you figure it out? I'm also not sure what the "Arbitrary dB" is.

On a different note, is there any way of choosing which trace you want to be visible? It seems to me that both the gain and the phase traces are always visible. AFAIK the sds2000x plus has this option but what about the SDS1x04X-E ? Is this feature missing?

Didn't really figure it out, but the values for Arbitrary dB seem the same as dBV. I'm not seeing an option to disable either trace and always see both.

[pope]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

I'm not seeing an option to disable either trace and always see both.

Yes, it's very annoying and I really don't see why the excluded this option for the 1104x-e. This sucks.

[WPE]

I am considering a Siglent SDS1202XE with SDG2042X - excited about the BODE PLOT II function and FFT along with a great oscilloscope - it would be my first new bench equipment in many years. 

My main initial application will be antique radio 456 kHz IF alignments with 2 and 3 stage variable BW IF's.  I've had some difficulty with my HP 141T spectrum analyzer and its 8443 tracking generator - and haven't found time to look into it.  I wanted "as-found" measurements before I start on these radios.  (I don't use that on simpler radios.) 

How practical is BODE PLOT II for a detailed look at these IF's?  I wonder if I would use sweep with demodulator probe to do real-time alignments, then follow up with the BP2 - or has anyone tried twiddling in small steps between waiting for another BP2 plot? 

FFT adds another dimension to it - would the FFT also be practical for a detailed look at these IF bandpasses?  Perhaps with noise input? 

I've read you can't really "replace" a good spectrum analyzer with BP2 in a multifunction "do-it-all" instrument - would I be much better off attending to my old HP141T combo for radio IF's?  (Then I would be curious about the phase data I could have had from BP2!) 

Or would this Siglent combo be a really good approach to this task?   

[BillyO]

I'm not a tube guy myself, but if you can attach the equipment safely to the DUT it should work fine.

One suggestion though.  The SDG2042X seems like a bit of overkill if this is your main use case.  For a bit less money than the two you are looking at you could get an SDS2104XP scope and enable the internal 25MHz AWG.  This scope will also do the Bode plotting, has 4 channels, a much larger touch enabled screen, can use a mouse & keyboard, has more triggering options, has all the same serial decoding and can be enabled for more, has more advanced measurement functions, has more advanced math functions, has higher vertical resolution (10-Bit vs 8-bit) and can be set to work up to 500MHz.

Just something to consider.

Either way, I think you will be pleased.

[tautech]

I am considering a Siglent SDS1202XE with SDG2042X - excited about the BODE PLOT II function and FFT along with a great oscilloscope - it would be my first new bench equipment in many years. 

The 2ch SDS1202X-E does not have BP as part of its feature set, maybe instead you meant SDS1204X-E ?

One suggestion though.  The SDG2042X seems like a bit of overkill if this is your main use case.  For a bit less money than the two you are looking at you could get an SDS2104XP scope and enable the internal 25MHz AWG. 

Actually the SDS2000X Plus range has an optional inbuilt 50 MHz AWG.

WPE, if as BillyO points out you instead consider a 2kX Plus do it soon before their $400 off promotion finishes at years end.
https://siglentna.com/news-article/sds2000x-plus-super-phosphor-oscilloscopes-promotions/