| General > General Technical Chat |
| Review: Hantek DDS 3X25. Anyone own one? |
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| zibadun:
--- Quote from: PuterGeek on December 19, 2012, 06:55:18 am --- --- Quote from: Mechatrommer on December 17, 2012, 12:32:17 am --- --- Quote from: PuterGeek on December 17, 2012, 12:10:31 am ---What would be a good cutoff frequency do you think I should use? --- End quote --- 100 or 200MHz? --- Quote from: PuterGeek on December 17, 2012, 12:10:31 am ---Maybe I'll whip up a schematic to share in case someone wants to try my idea. --- End quote --- yes please do. i will be interested. ;) --- End quote --- It is going to require a Bessel filter and will need to be more than 5 poles to get good results. I will need to run a simulation to verify some things and may need to probe around with my scope too. Not sure I will have this done before New Year because of the holidays but I am working on it. --- End quote --- I'd vote for 100 MHz or even 30 MHz cutoff frequency. The "sine" wave spectrum does not look very clean to me at HF (over 5-10 mhz). May be a good low pass filter will help with this. |
| PuterGeek:
--- Quote from: zibadun on December 23, 2012, 04:00:33 pm --- I'd vote for 100 MHz or even 30 MHz cutoff frequency. The "sine" wave spectrum does not look very clean to me at HF (over 5-10 mhz). May be a good low pass filter will help with this. --- End quote --- The filter will necessarily be a compromise. The maximum usable output would be about 80 MHz (40% of 200 MHz sample clock). If we only wanted sine waves we could use a 7 pole elliptical filter with quick falloff and get good results. But the elliptical filter phase delay and impulse response are horrible for arbitrary waveforms. A Bessel filter is usable but rolls off very slowly so it requires a lot of poles (9 or more). I'll try to post some simulation output later. p.s. I am a EE but not a filtering expert. This is based on my research on filtering AWGs. |
| alm:
Some AWGs use a different filter for sine output than for other signals. |
| PuterGeek:
--- Quote from: alm on December 23, 2012, 04:52:39 pm ---Some AWGs use a different filter for sine output than for other signals. --- End quote --- That would be possible but would be a more difficult mod to include inside the enclosure which was my goal. One way to do that would be to change the frequency counter input to a second output. An alternative would be external filters which is less appealing to me. |
| Mechatrommer:
there's plenty of room in the ds3x25, maybe you can use relay or something and switch to change the filter instead of providing 2 separate and simultaneous output. btw, i will love to further modify my ds3x25, but i already have entirely different plan for this "arbitrary wave generator project", the only problem is "Time". |
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