Products > Test Equipment
Siglent SDS1x04X-E BodePlot II (SFRA) features and testings
OwO:
It should be possible to increase dynamic range by adding a variable gain amplifier before the inputs right? You could pre-characterize the VGA at all gain steps and all frequency points during zeroing, and then during measurement it could auto-range at each frequency point.
Rerouter:
I was corrected earlier on another thread that it does uses the fine channel gain to extract the most vertical resolution it can from each frequency,
The full VGA gain and offset table is stored on the device, even the steps that do not end up being used, so they may be using them, but that would only net you a marginal improvement. I'm not yet clear on if ERES can be used in combination,
KungFuJosh:
After screwing around more, I mean experimenting, I realized my amplitude was too high for the DUT (first screenshot). The rest of the screenshoots are me "experimenting" more. At least they look cool, right? ;)
How can I reconcile the 50R terminated load on CH1 with a HiZ load on CH3?
For the bode plot to be accurate, do the waveforms need to match well? I tried offsetting the phase, which was about 120 degrees off, but that was never perfect, and the amplitude never matched. The closest was setting the amplitude to 90mVpp.
Thanks,
Josh
Performa01:
--- Quote from: OwO on July 02, 2019, 12:51:28 pm ---It should be possible to increase dynamic range by adding a variable gain amplifier before the inputs right? You could pre-characterize the VGA at all gain steps and all frequency points during zeroing, and then during measurement it could auto-range at each frequency point.
--- End quote ---
As explained in the opening posting, the Siglent Bode Plot offers the AGC feature already. Do you really think that 100 to 120dB dynamic range is not enough?
--- Quote from: Rerouter on July 02, 2019, 01:12:16 pm ---I'm not yet clear on if ERES can be used in combination,
--- End quote ---
No. The Bode Plot forces the Acquisition mode to "Normal" - and thankfully so, because the DFT filtering in the Bode Plot detector is far superior to the Eres lowpass filter, which might limit the upper bandwidth in an undesirable way.
--- Quote from: KungFuJosh on July 02, 2019, 02:31:04 pm ---How can I reconcile the 50R terminated load on CH1 with a HiZ load on CH3?
--- End quote ---
This is an oversight in the Bode Plot module. The next version will allow to specify separate load impedances for the reference and output channels.
Always specify the output impedance. In your setup it would be high-Z (as it is represented by the x10 probe) and for frequencies that low you could even connect the reference channel without a 50 ohms inline termination. The result will be correct as long as the reference channel sees the same amplitude as the DUT input.
--- Quote from: KungFuJosh on July 02, 2019, 02:31:04 pm ---For the bode plot to be accurate, do the waveforms need to match well? I tried offsetting the phase, which was about 120 degrees off, but that was never perfect, and the amplitude never matched. The closest was setting the amplitude to 90mVpp.
--- End quote ---
It normally should be just a single signal, fed into both the reference channel of the scope and the DUT input. For frequencies above some 10MHz, proper 50 ohms termination and a resistive power splitter is highly recommended.
You can also use the dual channels of the signal generator instead, but then it has to operate in Channel Coupled mode for amplitude, frequency and phase.
For higher frequencies, matched cable lengths are important to minimize the phase error.
KungFuJosh:
--- Quote from: Performa01 on July 02, 2019, 03:07:50 pm ---
--- Quote from: KungFuJosh on July 02, 2019, 02:31:04 pm ---How can I reconcile the 50R terminated load on CH1 with a HiZ load on CH3?
--- End quote ---
This is an oversight in the Bode Plot module. The next version will allow to specify separate load impedances for the reference and output channels.
Always specify the output impedance. In your setup it would be high-Z (as it is represented by the x10 probe) and for frequencies that low you could even connect the reference channel without a 50 ohms inline termination. The result will be correct as long as the reference channel sees the same amplitude as the DUT input.
--- End quote ---
Considering this oversight, it doesn't seem functional at all in my current setup.
--- Quote from: Performa01 on July 02, 2019, 03:07:50 pm ---
--- Quote from: KungFuJosh on July 02, 2019, 02:31:04 pm ---For the bode plot to be accurate, do the waveforms need to match well? I tried offsetting the phase, which was about 120 degrees off, but that was never perfect, and the amplitude never matched. The closest was setting the amplitude to 90mVpp.
--- End quote ---
It normally should be just a single signal, fed into both the reference channel of the scope and the DUT input. For frequencies above some 10MHz, proper 50 ohms termination and a resistive power splitter is highly recommended.
You can also use the dual channels of the signal generator instead, but then it has to operate in Channel Coupled mode for amplitude, frequency and phase.
For higher frequencies, matched cable lengths are important to minimize the phase error.
--- End quote ---
I'm reading that as "yes, they should match." I'm using both outputs from the AWG as described earlier in this thread. One is direct to the scope CH1 with a 50ohm adapter, and the other output goes to my DUT, which then goes through a 10x probe to CH3 on the scope.
With AWG CH2 locked to CH1, it doesn't appear that there's a way for me to have the waveforms match phase and amplitude on the scope.
Am I wasting my time with this? Is there any real benefit to the Bode Plot for audio equipment (specifically microphones and tube amplifiers)?
Thanks,
Josh
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