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Hey Lol,

Your nice old 485s come equipped with graticule markers specifically for
rise time measurement. See this video <> for
how to use them to get repeatable and comparable measurements between
scopes and signal sources.

Siggi
On Mon, May 21, 2018 at 19:46 lop pol via Groups.Io <the_infinite_penguin=
[email protected]> wrote:

On Mon, May 21, 2018 at 03:57 pm, Raymond Domp Frank wrote:

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

I have added another 485 for our assessment.
067-0681-01 /g/TekScopes/photo/50828/2?p=Name,,,20,1,0,0
and pg506 fast rise
/g/TekScopes/photo/50828/3?p=Name,,,20,1,0,0