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Another radio amateur about to buy a DSO ...

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Performa01:
Well, this is a 200 MHz scope, right?

From the plot I can see a VSWR <1.5 up to 340 MHz, so there is nothing to complain about.

Most likely there is a difference between the direct path up to 100 mV/div and above that, when the first internal attenuator gets switched in, e.g. 200 mV/div. With attenuator, the VSWR usually gets better.

2N3055:

--- Quote from: Performa01 on November 15, 2023, 11:11:27 am ---Well, this is a 200 MHz scope, right?

From the plot I can see a VSWR <1.5 up to 340 MHz, so there is nothing to complain about.

Most likely there is a difference between the direct path up to 100 mV/div and above that, when the first internal attenuator gets switched in, e.g. 200 mV/div. With attenuator, the VSWR usually gets better.


--- End quote ---

Anyways, it shows 50Ω path is not made by simply putting 50Ω terminator in parallel with 1MΩ/20pF input...

ebastler:

--- 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!

Performa01:

--- Quote from: ebastler on November 15, 2023, 01:13:17 pm ---This would be a nice opportunity to demonstrate the difference.

--- End quote ---
Was this not demonstration enough?

https://www.eevblog.com/forum/testgear/another-radio-amateur-about-to-buy-a-dso/msg5164407/#msg5164407

tggzzz:

--- Quote from: Mike99 on November 14, 2023, 08:44:05 pm ---
--- Quote from: bdunham7 on November 14, 2023, 03:04:28 pm ---
--- Quote from: Mike99 on November 14, 2023, 02:54:43 pm ---Here is the input VSWR measured on an FA-VA5 VNA (because my NanoVNA has a couple of inband spurious signals).

--- End quote ---

Are you using the basic calibration elements that came with the FA-VA5 or the better ones that they sell separately?

--- End quote ---

Shortly after I put that picture up I realised it was nonsense, and yes I do only have the basic cal kit for that VNA.

I fixed the problem with my NanoVNA and tried again, using the SMA cal kit that came with it. Not ideal at higher frequencies but needs must. The result may not be spot on but it's the shape I expected.

--- End quote ---

We all have the occasional brain failure!

Looks like I was right to question the statements in the earlier post shown below :(

A cursory inspection of the document referred to by Tautech would lead you to think that it has a 50ohm input.
    Channel Flatness (Inner 50 Ω)
    DC - 60% (BW): ± 1 dB
    60% - 100% (BW): + 1 dB/-3 dB
    Max. Input voltage
    1 MΩ: ≤ 400 Vpk (DC + Peak AC <= 10 kHz)
    50 Ω: ≤ 5V rms

A closer inspection reveals what I regard as specmanship...
    Impedance
    DC 1 MΩ: (1 MΩ ± 2%) || (18 pF ± 2 pF)
    DC 50 Ω: 50 Ω ± 2%

Of course only an owner can say whether that is significant in their application.




--- Quote from: tggzzz on November 11, 2023, 05:49:27 pm ---
--- Quote from: tautech on November 11, 2023, 05:44:58 pm ---
--- Quote from: tggzzz on November 11, 2023, 05:42:42 pm ---
--- Quote from: tautech on November 11, 2023, 04:06:46 pm ---
--- Quote from: Mike99 on November 11, 2023, 02:50:47 pm ---At a push I could go for the Siglent SDS2202X-E.

A 50 ohm input would be useful but I was planning to use a feedthrough terminator.

--- End quote ---
You do get more features with 2kX-E models.
1M/50 Ohm input path.

--- End quote ---

Are they 50ohm inputs or 1Mohm//50ohm//15pF inputs?

What's the VSWR, which is relevant at RF frequencies?

--- End quote ---
https://int.siglent.com/u_file/document/SDS2000X-E_DataSheet_DS0102E-E02A.pdf

--- End quote ---

VSWR isn't specified, which often happens where the manufacturer just puts a 50ohm resistor in parallel with the 15pF 18pF.

Any chance you could put a VNA on one of yours, in order to settle the issue?

--- End quote ---

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