Hi lop pol,
Thanks for doing the tests. I don't understand the outcome, however.
Just looking at your images:
In the TD (tunneldiode pulser) image, assuming a TD rt of 100ps (<=125ps specified), I see a 600ps rise time (rt), indicating about 590 MHz bw of the 485 against a spec. of 350 MHz. Even for that 'scope, it seems very high bw to me. 30% faster than spec'ed would be "normal", but 70%? Even with a theoretical rt of 0ps for the TD, the 485's bw would be about 580 MHz, about 65% faster than specified for this model! It *could* be caused by a slow 1 ns/div. time base speed.
A second strange thing is the suggested rt of the PG506 (pg). I see a rt of 1.6 ns. Assuming the specified rt for the 485 @ <= 1 ns (350 MHz), the pg's rt would be 1.24 ns, against a spec of < 1 ns. Not so good but possible, since the later (towards the top) part of the edge shows a speed reduction (shoulder rounding) that is not typical for this instrument. Also, the amplitude on the screen is a bit higher than used for the 485's specification, which could result in it performing a bit slower. Also, using the pg's variable attenuator would reduce its rt. BTW, the "slower shoulder" could be a side effect of using the attenuator pot to reduce the output signal!
So, two things I don't quite understand:
- Exceptionally fast (high bw) 485
- Exceptionally slow PG506.
Unless I'm mistaken in my observations, I don't see how to reconcile them.
Raymond
Raymond Domp Frank