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Oscilloscope input noise comparison
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jpb:

--- Quote from: _Wim_ on December 26, 2018, 12:59:40 pm --- Still dreaming of an 4262 with the bandwidth of the 5000 series (that is also affordable   ::) )

--- End quote ---
I'd like a 4 channel 4262 with an external reference input - this is unlikely to happen.

I'm dithering between a 4262 and something like an RME UX usb interface. If I want to measure 3 oscillators with a reference/calibration channel then this needs 4 channels.
The 4262 is the easiest solution but I can only ever measure 1 oscillator against a reference oscillator.
Using an 8 channel audio USB interface the frequency range is limited (1Hz to 80kHz basically), only 2 channels have pre-amps and setting levels is more of a pain. The noise figures are good though and it is a cheaper option.

If I want to measure 3 oscillators in a 3 cornered hat approach then I'd need 3 two channel 4262s as I'd have to use one channel on each for reference but it could be done on a single 4 channel 4262 if such a thing existed.
egonotto:
Hello,

@_Wim_: "Could you post a plot to 200MHz to check this with your 5444B?"

Perhaps we should ask this problem in the Picotech forum.

Best regards
egonotto


_Wim_:

--- Quote from: egonotto on December 28, 2018, 06:17:04 am ---Perhaps we should ask this problem in the Picotech forum.

--- End quote ---

That is a possibility, but as the spurs are "within spec", I do not expect much of an answer. I have been into contact with them a few times (using their feedback functionality build into the software), and although they are quite responsive, the answer is typically not very enlightening.
Andreas:
Hello,

at these sensitivities also the exact measurement setup is important.
The below 10 MHz peaks on Egonottos plot are shurely from a switchmode supply or from some other radiating cables nearby.
I usually separate carefully the power supply cable and the USB cables on my laptop.
(sometimes I also operate the laptop on battery only).

Attached 2 plots from my PS5444A with 50 Ohms terminator on the input.
One is with PS5444A outside my cookies box.
the other with PS5444A inside my cookies box (USB-cable hanging out)
So already there we have some (small) differences.
I guess that also a ferrrite on the USB-cable gives some improvement.

with best regards

Andreas



_Wim_:

--- Quote from: Andreas on December 28, 2018, 05:13:01 pm ---I guess that also a ferrrite on the USB-cable gives some improvement.

--- End quote ---

I have a ferrite on both USB and power cable, but when I installed it, I did not see a whole lot of difference. I also looked at the common mode noise "delivered" via the power cable, but did not find any correlation between the spurs and the common mode noise. Should do the same for the USB also. I will try to post some results of this later on.
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