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Picoscope Hack

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markone:

--- Quote from: _Wim_ on December 11, 2022, 02:33:58 pm ---
--- Quote from: markone on December 11, 2022, 01:40:40 pm ---Interesting, I would try with some other values for input resistor because with zero It would seem that aliasing could be a problem.

--- End quote ---

Might be worth a try, but I would have expected to see those aliasing effects in the spectrums measured above.

--- End quote ---

Do you have a sinusoidal signal generator capable to go over 200 MHz ?

_Wim_:

--- Quote from: markone on December 11, 2022, 02:57:24 pm ---Do you have a sinusoidal signal generator capable to go over 200 MHz ?

--- End quote ---

Yes, the CMU200 (can go to 2.7GHz), and you are correct, aliasing does occur for input signals > 300 Mhz (just did a quick test)

_Wim_:

--- Quote from: _Wim_ on December 11, 2022, 03:26:42 pm ---aliasing does occur for input signals > 300 Mhz (just did a quick test)

--- End quote ---

But even with the original 75 Ohm resistor, the aliased signal is only +-13dB lower (so a -20dBm 301Mhz Signal is aliased to 199Mhz 13dB lower as the input). Test ran in 12bit mode => 500MS/s

With the zero ohm resistor in place, we are -3dB only...

_Wim_:

--- Quote from: _Wim_ on December 11, 2022, 03:41:50 pm ---
--- Quote from: _Wim_ on December 11, 2022, 03:26:42 pm ---aliasing does occur for input signals > 300 Mhz (just did a quick test)

--- End quote ---

But even with the original 75 Ohm resistor, the aliased signal is only +-13dB lower (so a -20dBm 301Mhz Signal is aliased to 199Mhz 13dB lower as the input). Test ran in 12bit mode => 500MS/s

With the zero ohm resistor in place, we are -3dB only...

--- End quote ---

@egonotto, if you have RF generator that can send a 301MHz signal , would you be willing to run this also on your 5444B? I would like to know if this is an artifact from the "upgrade" or not. It could be that the LMH6574 is used to select between 4 anti-aliasing filters, and that the component values differ between the 5442B and the 5444B...

egonotto:
Hello,

here are 3 pictures with sine with 50 Ohm termination 100 MHz 301 MHz and 320 MHz

Best regards
egonotto

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