how to use the trigger function in the oscilloscope

Thread Starter


Joined Jan 31, 2008
Hello Forum,

if the signal we want to display on the oscilloscope is not periodic, say random, like a statistical signal, what type of triggering option do we choose?

It seems that there is a delay due to the flyback of the electron beam.

In periodic signals, the beam start again when the signal is at right level and slope ....

How about the AUTO trigger function?

Curiosity: what is the maximum frequency an oscilloscope can measure? 100s of Mhz, correct?



Joined Apr 24, 2011
Traditional "analog" oscilloscopes are very good at displaying periodic signals of short periods. They are of little use otherwisse.

A 'scope paints and repaints the wave it is presented with over and over. If it starts at the same given point (the trigger point) in the signal then you will see a stable image on the screen.

If the signal is not periodic, it has no reference point to keep redrawing from. Hence it is now doing something it is not designed to do. "Storage" scopes do exist that add a charge to the CRT to hold a single trace until erased.

A modern digital scope does a point by point data acquisition into digital memory and copies that array to the screen. Even given a single trigger it can acquire enough points to display the signal. It also has other advantages such as the ability to display the signal at an arbitrary time difference from the trigger, either before or after the trigger.

How far before the trigger it can display depends on how large it's memory buffer is.

An analog trigger is usually a fixed level as a + or - slope. Auto triggers look at the change (derivative) of the signal and can still be adjusted to ignore the slow parts and look at something faster.

The max frequency is a function of money: you only get the bandwidth you paid for.


Joined Feb 7, 2012
You have an analogue scope, if its small and relativly cheap its bandwidth could be only 20MHz. ie it will display a sine wave of this frequency correctly any faster and you get distortion. If its a 'large' oscilloscope and expensive maybe a few hundered MHz. Some go even faster.
But as above no use for fast random events.


Joined Mar 14, 2008
If the signal is truly random, then there is no point trying to trigger on the signal. The display will look essentially the same triggered or un-triggered (AUTO trigger or free running).


Joined Feb 10, 2012
Hallo !
Hapy to find this side I will put some questions abt scopes.
1.I have an HP1740 A whith user and service manual.
problem :- beam return is visible
- beam intensity is to low
The all U from stabilizators are OK.
2. I have also an HP 1332 A X/Y monitor with out any documentacions. On WEB find nul.... I will make time base for trigering and ......
Pleace some info ! Albert


Joined Feb 28, 2009
Does your scope have a "holdoff" control? That control can assist in allowing display of seemingly random yet similar signals such as decoded address pulses. If your scope is an analog type, you may have a difficult time seeing fast signals that don't occur at a fairly high degree of repetition.