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| Siglent SDG1000 (aka LeCroy WaveStation) firmware updates |
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| commongrounder:
I want to draw attention back to the sweep function of this generator. One of the often used functions for me is performing sweeps over the audio range and beyond. My other analog function generators (Tektronix FG504 and B&K 3020) have always produced the expected so-called "log" sweep, which is around a decade of upward frequency change over a particular period of time. I have also externally swept the generators at one octave per period of time. The first time I set up this SDG1005 for "log" sweep operation, I could tell right away that the frequency was not increasing as I expected. I put the generator on the scope and set up the graphing function for frequency over time. It seems to me that the rise is exponential (I have not calculated the values, someone better at math could do that). The sweep envelope does appear to match a couple of the built in arbitrary waveforms. I have shown below the graph from the SDG1005 and, for comparison, the same sweep set up on my Tektronix FG504. I would like to ask Siglent to change the sweep envelope for "log" to either octave/time or decade/time (or both). If someone has a suggestion for language to help convey that (mathematically or otherwise), I would appreciate the input. :) |
| Bored@Work:
First image looks like a logarithmic, second like an exponential function. The trick, however, to get a logarithmic display on an oscilloscope with a steady x (time) deflection is to drive the signal with the inverse function of the desired logarithm - which is an exponential function. |
| commongrounder:
Okay. Now the graph displayed on the scope screen shots has the x axis running in real time, i.e. linear seconds per division, so any instantaneous reading of the frequency at any particular time along that graph should fit the curve of the sweep I am desiring. By the way, I put log in quotes, because I came to understand that the rising curve of the sweep envelope isn't really a "log" function. I think this is where the firmware designers are missing the boat. The FG504 sweep envelope is what I am looking for. The scope is reproducing that envelope just as I expect. I have in the past plotted out the frequencies for the FG504 to be sure they fit my response plots. I am looking forward to being able to automate this process using the trigger output function of the generator. I also want to be able to use the arbitrary function to sweep a burst waveform to check peak power output over a range of frequencies with some automation. I can get an approximation of what I want by reversing the direction of the sweep, but it still is not conforming to either a decade or octave per time unit rise (or drop, in that case) in frequency. If you look at the little graphic on the generator screen in log sweep mode, you can see they have the correct visual idea of the "log" sweep function, but not the actual sweep. I am also wondering if they use one of the arbitrary waveforms as the envelope for the sweep. I haven't tried extending the sweep to the maximum time to see if there are discreet steps that suggest the 16k record length. I might try that next, just to get some additional insight. |
| commongrounder:
I went ahead and sorted out the math needed to create the proper sweep envelope for a decade "log" function. I am attempting to contact Siglent through their web site, but I am not at all certain that the messages are getting through, as there is no auto-acknowledgement email, or anything I have seen, so far. I surely am not the only end user who has issues with this. :-\ If anyone has a direct email address to customer service at Siglent they are willing to share, that would be great. Here is the formula with an example of an audio sweep of 20hz to 20khz over 10 seconds. f(t) = fstart * 10(t * c) c = log10(ffinal / fstart) / S where f(t) = a function giving the frequency in hz at time t t = the current time in seconds since the start of the sweep S = how long the sweep lasts in seconds (e.g. 10 seconds) fstart = the frequency at t = 0 in hz (e.g. 20hz) ffinal = the frequency at t = S in hz (e.g. 20,000hz) c = the 'time constant', as defined above (e.g. 0.3 for the example numbers above) |
| nixxon:
--- Quote from: commongrounder on April 29, 2013, 03:09:58 pm ---I went ahead and sorted out the math needed to create the proper sweep envelope for a decade "log" function. I am attempting to contact Siglent through their web site, but I am not at all certain that the messages are getting through, as there is no auto-acknowledgement email, or anything I have seen, so far. I surely am not the only end user who has issues with this. :-\ If anyone has a direct email address to customer service at Siglent they are willing to share, that would be great. Here is the formula with an example of an audio sweep of 20hz to 20khz over 10 seconds. f(t) = fstart * 10(t * c) c = log10(ffinal / fstart) / S where f(t) = a function giving the frequency in hz at time t t = the current time in seconds since the start of the sweep S = how long the sweep lasts in seconds (e.g. 10 seconds) fstart = the frequency at t = 0 in hz (e.g. 20hz) ffinal = the frequency at t = S in hz (e.g. 20,000hz) c = the 'time constant', as defined above (e.g. 0.3 for the example numbers above) --- End quote --- Where do you apply that function to integrate with the AWG. Do you make a waveform in MS Excel and export into the AWG? |
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