This makes me wonder now who got it first, Keysight or Siglent? This budget end scope market has really become quite competitive and when one rolls out a scope with specific features and specs for X dollars, it's not too much later before other brands start to follow with a similar product. In this case I wonder if Keysight was putting their 1000x series together and saw Siglents bode plot feature and thought they should include it as well.
I'm pretty sure Siglent copied Keysight.
The Keysight was released in Feb 2017, but I was given the prototype by a guy in a trench coat in the back alley at the Electronex show in Sep 2016
Copy what? Quite a hard accusation or suspicion.
Perhaps Keysight copied some others idea that also oscilloscope may have SFRA.
Perhaps also Siglent think same, independently of each others. If only copy idea that oscilloscope may have SFRA is it copying. Perhaps like Nissan or Lamborghini copy Ford.
Why I think this?
IF Siglent have copied Keysight this model perhaps then they release something total junk crap.
But because they did not copy they make something what is even some amount useful and not only for tell students that in the world there is also "BodePlot" and studets roll they eyes.
If you look Keysight scope time of release status (attached data sheet detail) you can easy see that this is really not copied by Siglent. Exept if you think that because BMW put 4 wheels under car then Nissan copy BMW and also do same - yes this level perhaps but more I believe that both have independently same idea. SFRA / BodePlot have been as long as I remember. Even I have owned (in history) real bit different "BodePlotter" ... Rohde&S SWOB. Perhaps Siglent get idea from R&S what is more like, as they have also copycat (not copy) some other features from R&S (clearly).
So, if you look this Keysight data sheet from release time.. you can see 10 samples / decade (later they have improved it bit because 10pts/decade was really like bad joke. Also it have 20Hz 20MHz limits and also it have only 1 channel.
Siglent have max 501 samples even down to 500Hz Span (1Hz step). Example, we have quite narrow 1.4MHz CW filter what need look... say example its width is 300Hz... If now take exaple 1000Hz Span so that 1.4MHz is center it can do samples 2Hz steps. (what can do system with 10 samples/decade).
If have some bit more complex circuit it can also take simultaneously 3 independet out from DUT.
Who can think Siglent copycat Keysight and then result is so much different and totally in different higher level of performance SFRA in Siglent SDS1004X-E. (but it do not have internal SG)
Also freq range is depending used external SG so it can do far more than 20MHz.
Of course also Siglent SFRA performance is far below real SFRA analyzers. First thing is poor dynamic range with its ADC. So, for look and adjust example high quality IF filters where stop band need be really far far below pass band it is just impossible to look this stop band. It is not tool for this.
Attached Keysight model (release time) data sheet detail about BodePlot
Siglent copycat this? Must have a really good ability of imagination.