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Another radio amateur about to buy a DSO ...

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ebastler:

--- Quote from: Performa01 on November 15, 2023, 03:39:17 pm ---Was this not demonstration enough?
https://www.eevblog.com/forum/testgear/another-radio-amateur-about-to-buy-a-dso/msg5164407/#msg5164407

--- End quote ---

Oh, right. For some reason I only remembered the pulse responses from your tests, not the return loss plots. Thanks for pointing them out again. Yes, those will do!  ;)

So the 2000X+ performs significantly better still than the 2000X-E -- which makes sense, given that it is specified up to 500 MHz. I am curious what it takes to improve the high-frequency matching. Presumably some of the "ingredients" cost money, and were hence not justifiable for the entry-level scope? So, besides properly chosen R and C as well as careful routing, what is required to get this right?

bdunham7:

--- Quote from: 2N3055 on November 15, 2023, 01:02:43 pm ---Anyways, it shows 50Ω path is not made by simply putting 50Ω terminator in parallel with 1MΩ/20pF input...

--- End quote ---

From the earlier discussions that I linked above, I'm not sure that is an entirely accurate explanation.  The external 50R across the existing 1M/20pF input also does not behave as you'd expect from a simple model using the stated values and depending on the exact terminator and setup, can perform much better than predicted--even if it isn't as good as the internal termination.

My theory was that the 20pF isn't just 20pF directly across the input but rather that it has some significant series resistance, not enough to matter in a 1M circuit but enough to take it out of the picture in the 50R case. 

G0HZU:

--- Quote from: Mike99 on November 14, 2023, 02:54:43 pm ---The deed is done. I bought the Siglent SDS2202X-E and they gave me a discount  :)

Mike

--- End quote ---

Sounds good! If you plan to use it for ham stuff (including transmitter testing) make sure you don't exceed the AC voltage limits (vs frequency) for a typical digital scope.

For the internal 50R load this is usually about 5Vrms across all frequencies within the bandwidth of the scope.

For the 1Meg input, I'd recommend you keep all RF signals below about 10Vrms, especially at mid to upper HF and into VHF. The scope will only be rated for high AC voltages at low frequencies. So you can't expect it to cope with (say) 400Vpeak above a few kHz. There may be a derating curve for AC voltage versus frequency somewhere in the manual.

Even a 12W PEP 27MHz CB radio can pose a risk of damage to some digital scopes unless you use some form of inline attenuation.

Mike99:

--- Quote from: G0HZU on November 15, 2023, 10:46:04 pm ---
--- Quote from: Mike99 on November 14, 2023, 02:54:43 pm ---The deed is done. I bought the Siglent SDS2202X-E and they gave me a discount  :)

Mike

--- End quote ---

Sounds good! If you plan to use it for ham stuff (including transmitter testing) make sure you don't exceed the AC voltage limits (vs frequency) for a typical digital scope.

For the internal 50R load this is usually about 5Vrms across all frequencies within the bandwidth of the scope.

For the 1Meg input, I'd recommend you keep all RF signals below about 10Vrms, especially at mid to upper HF and into VHF. The scope will only be rated for high AC voltages at low frequencies. So you can't expect it to cope with (say) 400Vpeak above a few kHz. There may be a derating curve for AC voltage versus frequency somewhere in the manual.

Even a 12W PEP 27MHz CB radio can pose a risk of damage to some digital scopes unless you use some form of inline attenuation.

--- End quote ---

Thanks for the advice! I'm having fun playing with low level stuff at the moment. Love the FFT function!

Mike

Mike99:

--- Quote from: ebastler on November 15, 2023, 01:13:17 pm ---
--- Quote from: 2N3055 on November 15, 2023, 01:02:43 pm ---Anyways, it shows 50Ω path is not made by simply putting 50Ω terminator in parallel with 1MΩ/20pF input...

--- End quote ---

This would be a nice opportunity to demonstrate the difference.
@Mike99, any chance you could repeat the measurement with the scope's input set to 1 MOhm and an external 50 Ohm pass-through terminator? Thanks!

--- End quote ---

I don't have a pass through terminator, only a 6dB BNC attenuator.

Mike

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