On Thu, 3 Jan 2013 14:26:04 -0700, David DiGiacomo
<daviddigiacomo@...> wrote:
On Thu, Jan 3, 2013 at 1:57 PM, micpreamp <micpreamp@...> wrote:
I have a 7904A with a 7A19 plugin (plus lots of slower ones, e.g. 7A24 and 7A26). I'd love to have two channels of > 500 MHz, and I'm contemplating if I should chase another 7A19 or get two 7A29 (and sell the 7A19). The 7A29 will make better use of the mainframe bandwidth and has a variable vertical deflection feature.
What I wonder: how do things look noise wise? I hate blurry traces, and I'm rather surprised how sharp the 7A19 is (much better than the 7A26!). Anyone who could compare them side-by-side?
Isn't that just due to the termination on the 7A19? Have you tried
putting a good inline termination on the 7A26?
Anyway, I haven't noticed a difference in trace noise between the 7A19 and 7A29.
The difference in noise between the 7A19 and 7A29 should be there
(maybe about 30%) but it will not amount to much and I doubt it would
be visible.
The 7A26 is so much noisier because it has a 1 MOhm input impedance.
The higher noise levels involved with high impedance inputs is why you
do not find high bandwidth and high sensitivity in the same amplifier
for a given input impedance. I actually prefer the 7A26 (200 MHz
switchable to 20 MHz) or 7A13 (100 MHz switchable to 5 MHz) to the
7A18 (100 MHz only) because they have switchable bandwidth limiting
which makes a large difference in displayed noise when you do not need
the higher bandwidth.
David Hess