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R&S SML01 1.1Ghz Generator
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G0HZU:
If it helps, I can list a few things that can add to the overall uncertainty if you simply buy a decent 1GHz sig gen that has had a recent calibration and use it to test the 1GHz scope.

The first one is level uncertainty. This might be as good as +/-0.1dB (typical) up to 1GHz but it could be +/-0.2dB. It could be as bad as +/- 1.5dB for an older mid range sig gen that has an upper limit of 1GHz. This is because the manufacturer will opt for a more basic (cheaper) ALC system that will work well up to about 700MHz but then degrade a bit towards 1GHz.

Therefore, it's best to buy a sig gen that has optional versions that can go to several GHz as they will probably all share the same ALC (levelling) system that will be good to several GHz. The Agilent ESG series has very good flatness for example and these seem to start at about £600 on ebay.

Then there is mismatch uncertainty between the source and the load. The source VSWR of your sig gen at 1GHz at (say) +6dBm might be 1.3:1. The input VSWR of your 1GHz scope might be 1.5:1 at 1GHz. This contributes another +/- 0.23dB uncertainty to the overall system.

Then there is the loss in the connection cable and this could easily be 0.5dB at 1GHz for a decent RF cable with low VSWR.

This stuff soon adds up and a lot depends on what you consider to be acceptable.
nctnico:

--- Quote from: Bud on July 22, 2023, 05:45:33 pm ---Have you considered using a pulse gen and derive the DUT scope bandwidth from rise time?

--- End quote ---
That won't work because it assumes a certain roll-off factor that isn't fixed on oscilloscopes. The only way to determine the bandwidth of an oscilloscope is to use a levelled RF generator.
rsjsouza:

--- Quote from: G0HZU on July 22, 2023, 07:23:11 pm ---Then there is the loss in the connection cable and this could easily be 0.5dB at 1GHz for a decent RF cable with low VSWR.

--- End quote ---
I haven't tested the bandwidth of an osciloscope, but on the VNA the choice of adapters and connectors can add a few fractions of a dB here and there - especially if you happen to grab a random cable and/or adapter from the lab's shared drawer and waste quite some time trying to figure out why the darn response seems off... :palm:

That and curves and kinks on the cable, whose influence is much more severe on a sensitive equipment such as a VNA.
nctnico:
At frequencies over 1GHz you need to check the specs of the cable and use really short cables as well. I have a few short Huber+Suhner RG223 cables I use for measurements where cable loss must be low.
Performa01:
I don't have a specific recommendation, but a few general hints:

* Testing the bandwidth of a scope is not a precision task in my book. Even an error up to 1 dB would not really matter that much. Take for example my measurement of the SDS2504X Plus, where a 1 dB error caused by the cabling accounts just for the difference of 570 to 605 MHz. Are we really that desperate to brag about the bandwidth of our darling scopes that such a small difference matters?
* As others have already hinted on, you want a sine, not a square as its output by some cheap toys. Dead giveaway: if there are no specifications for the harmonic distortion, then don't touch it!
* Get some 10 dB inline attenuators so you can optimize the port impedances. A quality signal generator will have a good VSWR as long as its attenuator is active (i.e. you don't demand the full signal amplitude), but the scope input VSWR might be as bad as 1.5:1 at the bandwidth limit and far worse beyond that. The resulting error is not huge, but the measurement trace looks prettier if it has no wobble in it ;)
* A quality signal generator is "levelled", i.e. its output amplitude is measured and controlled in a way to make it as constant as possible. Tracking generators are not. You can build your own precision levelling circuit as pictured by G0HZU, but this requires quite some gear and you'll probably lose the ability to sweep the signal generator - and therefore the simple way to let the scope plot its own frequency response. Real automation might be no fun with ancient gear that only provides GPIB (or nothing at all), and it most definitely is a pain if you have to do it by hand...
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