| General > General Technical Chat |
| Review: Hantek DDS 3X25. Anyone own one? |
| << < (68/108) > >> |
| alm:
Shafri would know for sure, but I would expect the only result to be that the software does some mathematics to convert the amplitude display. 1 ohm output impedance sounds unlikely, that would suggest a huge short circuit current. It's also very uncommon for generators to actually have a variable output impedance. |
| Tectonic:
As far as I know the Spartan 3 has digitally controlled impedance functionality. I can't be certain if this is how the GolTek Controller varies output impedance though. |
| Mechatrommer:
--- Quote from: Tectonic on November 24, 2011, 10:42:57 pm ---With the BNC cable, the scope is set to 50ohm. With the probe the scope is at 1Mohm. I reduced it to 1ohm via software. --- End quote --- preface: software is a software, it got nothing to do with hardware. goltek cannot control the hardware impedance, there's no API for that. if you look at teardown in the early page, dds3x25 only has fixed 50ohm output impedance, ie small resistor just before the bnc connector output. by changing impedance in software, it will not affect anything in the hardware. "postface": what impedance means in goltek is that... in reality, at what impedance you are loading the generator? (a resistor between the 3x25 output and the ground, it also called termination) if you set your scope to 50ohm (scope's input impedance), then you are loading the 3x25 with 50ohm, then you should put 50ohm value in software. if you put a 1 ohm termination at the probe, then put 1ohm in goltek, not the other way around, dont expect by putting 1ohm in software, there will be a 1 ohm resistor popped out somewhere in reality. impedance value in software is only try to display/simulate/predict the signal magnitude correctly... you have to match the impedance in real world, with the impedance value in software so that the little "monitor like" figure simulating output signal in your PC, will show you the closest thing with the real signal out of the 3x25. i hope i understand your problem correctly and answered it. ;) |
| Mechatrommer:
as of your picture. the 1st picture is scope impedance set to 50ohm (software at full magnitude), the 3rd picture the scope is set to 1MOhm impedance (and again software at full magnitude), and the 2nd picture is some reflection from the pomona lose wires probe or else the goltek already change amplitude setting to lower value due to you are playing around with "software impedance". am i right? i suggest you redo test in 2nd picture, but make sure magnitude setting in goltek is set at maximum, if the pomona+scope impedance = 1MOhm, you should see 6Vpp (similar to 3rd picture, or 3Vpp like in 1st picture if your probe+scope "real" impedance is 50ohm) but noisy wave (noise due to improper probe setup, ie lose wires), hint: to get max magnitude in goltek, just type crazy large value such as 1000V and hit enter, goltek will automatically set to max magnitude sensible by the API (hence DDS hardware). and make sure Flat Ctrl is turned OFF if you want max 6Vpp out of 3x25 (Hi-Z output) |
| rev0:
--- Quote from: Mechatrommer on November 25, 2011, 12:27:34 am ---as of your picture. the 1st picture is scope impedance set to 50ohm (software at full magnitude), the 3rd picture the scope is set to 1MOhm impedance (and again software at full magnitude), and the 2nd picture is some reflection from the pomona lose wires probe or else the goltek already change amplitude setting to lower value due to you are playing around with "software impedance". am i right? i suggest you redo test in 2nd picture, but make sure magnitude setting in goltek is set at maximum, if the pomona+scope impedance = 1MOhm, you should see 6Vpp (similar to 3rd picture, or 3Vpp like in 1st picture if your probe+scope "real" impedance is 50ohm) but noisy wave (noise due to improper probe setup, ie lose wires), hint: to get max magnitude in goltek, just type crazy large value such as 1000V and hit enter, goltek will automatically set to max magnitude sensible by the API (hence DDS hardware). and make sure Flat Ctrl is turned OFF if you want max 6Vpp out of 3x25 (Hi-Z output) --- End quote --- I'd like to suggest the addition of a PWM waveform option on your Goltek program. I don't yet own a 3x25, but just ordered one, and I think that a variable frequency and duty cycle PWM output would be extremely useful (I usually end up programming an AVR to do this, but I waste a lot of time hooking one up and digging out the right config register values). |
| Navigation |
| Message Index |
| Next page |
| Previous page |