Products > Test Equipment
Siglent SDS1x04X-E BodePlot II (SFRA) features and testings
graybeard:
I verified last night that the Bode Plot II function works great up to 120MHz with my "upgraded" SDS1104X-E and my "upgraded" SDG2042X.
This was my mane reason for upgrading the function generator since it other wave forms are limited to 25MHz regardless of the upper frequency limit for the sine function.
As the frequency increases you need to be far more careful about proper terminations. The scope needs both a 50 feed through termination and at least a 6dB attenuator for flat response all the way out to 120 MHz.
rf-loop:
--- Quote from: graybeard on December 04, 2020, 06:36:26 pm ---
--- Quote from: khutch004 on January 10, 2020, 05:10:20 pm ---For really-high-quality audio power amplifiers, a bode plot of the range 0.1 Hz to, say, 100 Hz will enable a designer to accurately predict the audibility of artifacts coming from attempts to limit the vlf range by steep slope high pass filtering of subsonics.
People building bass guitar amps and high pass filters for them are interested in evaluating the very low frequency response. They often use an HPF to prevent the cone excursions from exceeding safe limits if subsonic information appears at the amplifier inputs. Bass cabs often walk a fine line between being able to generate a high output level at 30 to 60 Hz and blowing up when presented with low frequency noise and often some help from the amp or a filter in front of the amp is needed.
A better question to ask is the 10Hz low limit arbitrary or is it driven some important cost or reliability concern?
If it was just an arbitrary limit then why NOT extend it as far as possible?
People building filters for some scientific applications will want to test at sub 10Hz frequencies. There may not be terribly many such people but again if the limit is arbitrary then it should be removed.
--- End quote ---
I suspect the 10 Hz low frequency limit is due to the low frequency roll-off of the AC coupling on the scope since it always changes to AC coupling for the bode plot function. The AC coupled low frequency roll off -3dB point is speced at ≤2 Hz. For gain flatness you want to be at least a decade above that.
--- End quote ---
This AC response in Siglent these models have quite low f corner. Data sheet do not tell lot, only rough ≤2 Hz -3dB.
Here attached one individual scope response. I have fast checked roughly some other individuals previously and they looks like in same ballpark. 10Hz low limit in SFRA is imho ok for this response. It is, imho, best that this BodePlot freq selective receiver is AC coupled.
Bode plot upper limit 120MHz is bit too high but if users know its limits it is still nice have this upper limit than half of it.
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Inside SDG2000X is possible to tweak some other wfm limits but mostly result is way or other bad.
Of course example if rise triangle upper limit it can do... it can do lot. But... linearity is not then what is told in data sheet and as can see have done in some elcheapo generators due to fact they just want show higher number in data sheet. Also some other limits can break... but always there is then some negative side effect. Limits are just compromise between many variable things.
I have not done these experimentals with SDG2000X But with 1000X. What is - if think system software - very very close relatives.
One random individual SDS1104X-E, 0 - 10Hz fresponse when AC coupled.
rf-loop:
--- Quote from: graybeard on December 04, 2020, 06:40:34 pm ---
As the frequency increases you need to be far more careful about proper terminations. The scope needs both a 50 feed through termination and at least a 6dB attenuator for flat response all the way out to 120 MHz.
--- End quote ---
It is pity we do not have feed thru terminators what are matched for oscilloscope reactive inputs so that terminator input looks good 50ohm impedance over whole freq range instead of only for "DC" or near DC like audio etc.
Who will start make these kind of tunable feed thru terminators for 1M xC xL inputs in oscilloscopes. I do not believe any scope manufacturer start do scopes what have real 50 ohm input impedance when we talk these cheap oscillocopes. Because if they do there need do whole other parallel input stage for this and not just relay connected parallel resistor to ground from input center line.
tautech:
Siglent BP II App Note:
https://siglentna.com/wp-content/uploads/dlm_uploads/2019/05/Measuring-Power-Supply-Control-Loop-Bode-Plot-with-Bode-Plot-%E2%85%A1.pdf
pope:
Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.
I am using the 1104x-e with a sdg1032x and I'm having the following problem...
If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.
Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...
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