Re: Don't fix if it ain't broke or preventative maintenance

Marian B

The average HP 3400A has a -3 dB bandwidth of about 5 Hz to 20...25 MHz.
I guess that in fact the 3400A set the 20 MHz bandwidth standard for
this kind of measurement. Maybe even Tek themselves used 3400A's?

(The 10 MHz spec of the 3400A is a +- 5 % bandwidth i.e. +- 0.5 dB)

Cheers, Marian

On 16.01.2016 04:37, Sigurður Ásgeirsson siggi@... [TekScopes] wrote:

Hey Dwayne,

In the service manual for the 2400-series scopes it clearly specified to
use 20MHz bandwidth for PSU ripple measurement. I also believe it's a
de-facto standard for this, as noise is a monotonic function of bandwidth.
That being said I checked the service manual for my 485, which just lists
acceptable ripple without further spec.

On Fri, Jan 15, 2016 at 21:52 Dwayne Verhey yg@... [TekScopes] <
TekScopes@...> wrote:


I'm curious where you get the 20MHz specification. The manual calls for
a scope with "Bandwidth, DC to 100 mega-hertz; minimum deflection
factor, five millivolts/division; accuracy, within 3%, and the example
given is the Tektronix 454A Oscilloscope with two P6054 probes (which
Google says are 150MHz and 250MHz, respectively).

I'm not saying you are wrong, the test scope is also to be used for
other things like the high-speed timing adjustment. I just don't see
anything in the manual about 20 MHz (mind you, these manuals often
assume some basic level of prior knowledge and experience, which I don't

I certainly get your point about the persistence of a digital scope
compared to the old analogue. Even with the intensity cranked up to
maximum, the 475 trace is pretty faint at the fastest time base settings
using the delayed sweep function. Even though the 475 is rated at 200MHz
bandwidth and the Rigol is rated equivalent to 150MHz (mine is upgraded
to the DS1152E-EDU spec), It's a darn sight easier to catch and study a
transient or high-speed waveform displayed on the digital scope!

That said, at slower time base settings, I really like the "feel" of the
475 analogue display compared to the Rigol. The variations in intensity
and the smoothness of the curves highlight the pixellation of the
Rigol's display. Now if only it was in colour...

On 15/01/2016 8:45 PM, Sigurður Ásgeirsson siggi@... [TekScopes]

The noise and ripple is typically specified at 20MHz bandwidth. Also
beware that it's specified as seen on an analog scope of the time.
Digital scopes may show higher noise and ripple, as depending on
such as memory depth. Effectively they can be set to more persistence
the phosphor of the old-style analog scope.

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