Products > Test Equipment
Oscilloscope input noise comparison
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TheSteve:
On the Keysight 3104 the 50 ohm path is a different input on the front end ASIC.
2N3055:

--- Quote from: TheSteve on November 14, 2018, 10:13:31 pm ---On the Keysight 3104 the 50 ohm path is a different input on the front end ASIC.

--- End quote ---

As I stated above, there is visble change in RMS noise level when changing from 50 \$\Omega\$ to 1M \$\Omega\$, but it is not great...

I will be traveling for few days. When I get back I will repeat measurements.
I would like to see somebody's else 3104T noise figures...
Maybe my 3104 is noisy.

TheSteve:
I can post mine but it will need a big star next to it as it's a MSOX3024t modified to 1+ GHz.
ci11:
Teledyne LeCroy HDO4032 12-bit 350MHz, no averaging, no ERES.

DC50 Ohm

 20MHz                   62,90 µVrms   312,44 µVpp
 350MHz               124,37 µVrms   847,66 µVpp

DC1M Ohm

 20MHz                   83,95 µVrms   313,00 µVpp
 350MHz               165,33 µVrms   899,47 µVpp

DC50 Ohm data:
 
 20MHz BwL DC50 Ohm
 350MHz DC50 Ohm

DC1M Ohm data:

 20MHz BwL DC1MOhm
 350MHz DC1MOhm

A couple of interesting points from the FFTs: the 20MHz BwL seems very gentle but still effective as can be seen in the numbers, and for a 350MHz scope, it appears to have BW well beyond 1GHz. Perhaps the folks at LeCroy do not believe in brickwall filters.
rf-loop:

--- Quote from: maxwell3e10 on November 14, 2018, 10:09:32 pm ---Here is a comparison of Keysight MSOX2024 and MSOX3104. They have very similar noise performance. Another peculiar thing is that MSOX3104 has virtually identical noise on the 1 MOhm and 50 Ohm setting. I guess it means that the scope doesn't have a different front end amplifier, just an internal 50 Ohm resistor switched across the input.


--- End quote ---



Of course these graphs and tables and curves are nice and useful.
Btv, is it possible to keep all graphs vertical scale and position in scale same for more quick and easy compare without thinking. 

But then also, what we do IRL. We look oscilloscope screens and it also matters what we really see (and measure).

Like these:
first @srce previously published  MSOX2024A - 200MHz - 2GSa/s - 1mV/div - 1MOhm
then same settings with SDS1204X-E. same BW, 1M input, 5us/div  but samplerate 1GSa/s (and memory of course due to samplerate and time scale "equal")

Not very easy imagine what is visible on the screen if only look V/(Hz1/2) graphs.




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