Signal Profile Concept and File Format

Signal Profile File is a csv formatted file storing voltage (attenuation) amplitude of the Output Signal of Hantek DDS3x25 (or its add-on device). It acts as a lookup table for Goltek Controller to compensate for Flat Signal and Bandwidth Limitation. A brief explanation on how its done is discussed in Flatness Control and Bandwidth Limitation. Let's look at what's inside... This is how its looks like in Ms Excel (figure below). The first line showing how many data available, i've deleted some of them for simplicity, originally there should be 108 data (row). The second line is the output impedance of The Hantek device, you can get the value from your device specification manual, or more reliably it can be retrieved by measuring the resistor just before the device + output impedance of the opamp driving it (LMH6702), in the example below, the total is 49.92 ohm. The 3rd line is just labeling to show what's in each column stand for. Our data start at 4th line, there's 3 column in each data, ie frequency, max and min voltage, at the time of this writing, the 3rd column is not implemented and will be ignored, it is assume the output signal will be symmetrical, ie min = -max volt. We only look at the 1st 2 column, ie frequency and its max voltage.

Each frequency will have its own max amplitude (voltage), the greater the frequency, the lower the amplitude, this is the common profile for most devices out there. From a rough study, Hantek 3x25 is specified as 38-40MHz signal generator at -3dB output attenuation. As discussed in Flatness Control and Bandwidth Limitation. Goltek Controller will use these values to determine the flat (limiting) voltage at certain frequency. we also should be aware that, if we put wrong voltage amplitude in the Profile File, the software will calculate the wrong scaling for signal output, ie what you see (volt) in the software, is not what you are getting (WYSI "N" WYG). Then how do we profile our Hantek signal correctly?

Well, the answer is we need to profile our device on our own (since Hantek didn't provide the data for us), and probably with super expensive super reliable measuring device such as high bandwidth oscilloscope of at least 1GHz! why? as i said, if you measure it wrongly, you'll get wrong result to be saved in the profile file, and hence garbage output. Anyway, i've done it, with cheapo DSO, should i / you care for its accuracy? yes? then you should not care taking out your big bucks of multi thousands dollars to get the reliable measuring equipment for it. or if you clever enough, you can get someone to profile the device for you for free, or at fractions of the measuring equipment.

how is the process? for the specific case of our Hantek device? simple, we send an uncompensated (Flatness Ctrl OFF and unprofiled (no profile) signal) of full swing of 3.5V signal from PC software (Goltek Controller) to the Hantek and visually look at the peak to peak voltage of the signal through measuring device such as DSO and start tabulating the Profile File, easy isn't it? well it depends on how much data/frequency you want to profile, the more data, the more time required to do the profiling job. At the time of this writing, i've not develop the Goltek Profiler yet (and Goltek Compensator) that suppose to do this job easily, so the only method we have right now is to manually profile our device and manually edit the Profile File according to the format in the figure above. In the Goltek App Folder (\profile), i've included my Signal Profile File (profile3x25.csv) that i've made earlier using my simple tool. I've made the file as default signal profile for Goltek Controller the first time its loaded. Its good enough for me and i hope its good enough for you as well, albeit inaccuracy for being measured with unprofiled (unreliable) measuring devices. In case you need more accurate signal profiling, you can manually edit that file to suit your need (1st and 2nd column) or copy/rename it to another file, but you need to leave (edit) the format intact, ie the label, data count at cell B1 (above figure), impedance value at B2, data start from line 4, and 3 columns each line (even though the last column is ignored). And it only accept US style of csv, ie comma "," as separator and dot "." as decimal point. And please note, since i've made the profile3x25.csv file using another tool (engine), it may be slightly off when used in Goltek Controller which is based on newer generator engine. But so far from my observation, its pretty close. To unload any signal profile, whether you dont need one or are going to do signal profiling process, you can load the (profile_none.csv) in the same folder as the profile3x25.csv.

I think That's It!

 

 

 

 

any comment, improvement and suggestion, please contact me at soasystem@yahoo.com
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