Analog scopes for noise measurements

[Joerg]

Hello John,

DSOs sample continuously so they can display pre-trigger samples, so
it's too late to change the true sample times once the trigger
arrives. All you really need to do is quantify the delta-t between the
trigger and the next (or in fact any known) sample, and fudge the
display accordingly. That's not real hard to do.

You are right, won't work for pre-trigger stuff. We don't have that
problem in ultrasound since there is nothing around before the transmit
pulse, so I rarely have pre-trigger situations ;-)

Still, I am not too fond of even 1Gs/sec scopes. At least for repetive
signals with some random and nasty noise in there the analog scopes
often run circles around the DSOs. Unless you shell out really big
bucks, of course.

Another typical situation is phase noise or EMI self-pollution. There
you sit with a huge box over the scope and look for that wee thickening
of a rising edge when something is turned on or off in the system. Not a
chance with a regular upscale DSO.

Regards, Joerg

http://www.analogconsultants.com

 

[John Larkin]

On Wed, 03 Aug 2005 20:44:46 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello John,

DSOs sample continuously so they can display pre-trigger samples, so
it's too late to change the true sample times once the trigger
arrives. All you really need to do is quantify the delta-t between the
trigger and the next (or in fact any known) sample, and fudge the
display accordingly. That's not real hard to do.

You are right, won't work for pre-trigger stuff. We don't have that
problem in ultrasound since there is nothing around before the transmit
pulse, so I rarely have pre-trigger situations ;-)

Still, I am not too fond of even 1Gs/sec scopes. At least for repetive
signals with some random and nasty noise in there the analog scopes
often run circles around the DSOs. Unless you shell out really big
bucks, of course.

Another typical situation is phase noise or EMI self-pollution. There
you sit with a huge box over the scope and look for that wee thickening
of a rising edge when something is turned on or off in the system. Not a
chance with a regular upscale DSO.

Regards, Joerg

http://www.analogconsultants.com

Well, after years of analog scope-dom, I have surrendered. I love my
TDS2012 for anything but really low-level analog stuff or really fast
things. The color and infinite storage are wonderful, and the whole
thing is the size of a shoe box.

And the TDS3052 (500 MHz) scope with the fet probes is far cleaner
than any similar-speed analog scope using passive probes.

We do keep a monster 1 GHz 7104 around for the strange cases, fast
analog stuff or microvolt differential. But I now find the monochrome
CRT to be quaint and confusing.

John

 

[Joerg]

Hello John,

Well, after years of analog scope-dom, I have surrendered. I love my
TDS2012 for anything but really low-level analog stuff or really fast
things. The color and infinite storage are wonderful, and the whole
thing is the size of a shoe box.

They are nice and I have to confess that I did find stuff like runt
pulses with DSOs that an analog scope would never have shown.

And the TDS3052 (500 MHz) scope with the fet probes is far cleaner
than any similar-speed analog scope using passive probes.

This ain't fair. Then the analog scope has to get a FET probe as well.

I am using the Philips probe. That thing is tough. Once the mains plug
adapter (its a Euro version) fell off and so I accidentally plugged it
into the 230V lab rail. It took me about 10 minutes to find out why I
couldn't zero the offset. Almost burned my hands on the PS. Plugged it
into the 120V rail and bingo, it worked like a champ again.

We do keep a monster 1 GHz 7104 around for the strange cases, fast
analog stuff or microvolt differential. But I now find the monochrome
CRT to be quaint and confusing.

But the old green glow has that real "engineer feel" to it. Until a CRT
croaks and you receive the spare parts quote.

Regards, Joerg

http://www.analogconsultants.com