Square wave generator - problems

I have been starting to use a 10-15 year old Farnell sine wave generator
It does have a square wave output
I seem to be a bit stupid because on the scope the square wave I see - just horizonantal lines top and bottom of the scope - no vertical lines joinign the top and bottom up at all

Is it kaputt or am I being daft?

heres a photo of the generator

[quote author="uk03878"]- no vertical lines joinign the top and bottom up at all

Is it kaputt or am I being daft?[/quote]
I'm not sure whether you're kidding us or not - I mean, if it was April 1st I hadn't taken the risk to answer :wink:

But OK, can you zoom in on the sections where you'd expect the transition ? It'll simply be a matter of very fast transitions of that square wave output and you might be using a scope-setting that's not able to display them I expect. The 'problem' of the 'missing verticals' might even be 'worse' for lower frequencies as the rise & fall times of the square wave will stay relatively unchanged while the time as needed on the X-axis to display a whole period increases.

Bye,

Peter

erm....

er....

I'm only continuing because I'm trusting that you're not actually pulling our leg here...

Have you thought about HOW the beam gets from the bottom line to the top line? -DAMN FAST!!!

-Now, bear in mind that the beam is putting out an even. steady beam of electrons. On a flat horizontal line (silence or DC) that mans that they group together very closely. Think of a ball-point pen that has a flow-rate restriction and the ink flows at a constant rate no matter how fast the ball turns. Now, draw a steady horizontal line and you'll see that it is thigk and dark. Draw a lightning fast vertical transition (the horizontal rate is unchanged and steady, but now it has to get from bottom-of-the-screen to the top in ZERO microseconds or as close to zero as is physically (literally) possibe and you'll see that the pen is moving faster than the ink can flow sufficient to draw a heavy line any more.

-Proof? -Turn up the brightness... WAY up!!! Now do you see the transitionts?

-Basically, the dimness of the transitions is a sign of excellent HF response. the brighter the lines, the slower the transition meaning the more "electron-ink" gets to hit the "screen/paper".

-Personally, I think you really knew all this and you're just foxing; -fishing for compliments on your Scope/generator bandwidth.

-Bighead.

-I hate you.

:wink:

Keef

I wasn't pulling your leg - honest
A wise man once said - no question is daft if you don't know the answer
He obviously hasn't met my missus then

thank you both - am off now to buy a can of "bleeding obvious if you sit down and think about it"

All fine, enjoy the gear (& that can) :thumb:


Bye,

Peter


Ah, w.r.t. risetime, there was this occasion during studies that a person got goofed by two others. Further ingredients are a scope and a BNC-cable. While one very visibly puts the loose end of the cable in his mouth & starts giving the impression that he's blowing air into it, the other conspirator quietly turns up the DC-offset dial, resulting in a rising zero-level of the trace on the scope.
The third person, not that experienced with testgear, doesn't know how to understand all this and looks very confused at the screen while not noticing the hand at the zero-adjust-knob. :wink:

Crank up (or down, in value) the timebase and you should see the vertical line eventually. Perhaps it will even start to tilt...


M@

[quote author="uk03878"]I wasn't pulling your leg - honest
A wise man once said - no question is daft if you don't know the answer
He obviously hasn't met my missus then [/quote]
www.thingsmygirlfriendandihavearguedabout.com :wink:

Cool. -Of course, with faster horizontal timebases, you expect the line to get dimmer, but then it's refreshing and repeating, so that re-brightens again...

Yes, if you wind the timebase up to the speed of light, it will eventually ahow you a slanted line (unless your genny and scope are developed from secret alien technology!) and this'll help you see how good your gear really is!

In other words, a TRUE square wave has infinitely fast time, and gets from all-down to all-up in ZERO time, therefore there is ZERO line drawn.

You can put it through a low-pass filter and see that the first thing is a sloping and brightening of the verticals... Gives you a nice 'feel' for it all.

Keith

Its everybodies pictures of lines going vertical that made me feel inadequate
Now I know it's either the camera shutter speed or you have been fooling with the timebase and brilliance

...or people have tried responding to the "does your lack of verticality make you feel inadequate?" emails! :wink:

Keef

Here's a good wave:


And a not-so good wave:


-You can see that good HF response makes for less-visible verticals.

Even on digital (usually LCD) displays, the verticals get thin, but they have to draw a line. When there's no noise on the signal though, this type of display shows an artificial 'width' to the verticals...


..kinda like this:


Keith

I rarely ever see much of the vertical wave part of a square wave on my scope or any of the ones at school, I just assumed this was just the way it was.