X-Y scope mode; diagonal line...

[glossywhite]

Hey folks

I have a Tek 2445A, into which I am feeding two sine waves; 1000hz X, 1002hz Y. When I feed them and observe in X-Y mode, as well as the pretty rotating circle, I have an intense diagonal line, heading from bottom-left to top-right:

I know this must be something mega simple, but this 'scope is SO new to me, with so many knobs and doo-dahs... help?

Thank you

 

[DerStrom8]

Could you post a photo?

 

[glossywhite]

Could you post a photo?

Done (edited OP)

 

[DerStrom8]

Done (edited OP)

Thanks!

I have seen that before, I just can't remember the circumstances. What are you using to generate the sine waves?

 

[glossywhite]

Thanks!

I have seen that before, I just can't remember the circumstances. What are you using to generate the sine waves?

I'm using "Audacity"; one frequency for left channel, the other for right.

Thanks

 

[DerStrom8]

Well the diagonal line would show up if the sine waves were equal in frequency. The rotating circle happens when they're not in sync (frequency differences). It looks like you're at just that point where it's close enough to show the line but different enough to display the rotating circle....

What happens if you play a 1khz sine wave through through both channels? Do you see just the straight line?

 

[glossywhite]

Well the diagonal line would show up if the sine waves were equal in frequency. The rotating circle happens when they're not in sync (frequency differences). It looks like you're at just that point where it's close enough to show the line but different enough to display the rotating circle....

What happens if you play a 1khz sine wave through through both channels? Do you see just the straight line?

No, I see a cross

 

[DerStrom8]

No, I see a cross

Really? Photo please

That makes me think there is another signal that shouldn't be there. Perhaps it's picking up mains hum on both channels? Are you using actual probes, or just headphone wires? You're probably getting some interference from somewhere else.

Using a computer sound card really isn't the best way to generate signals for a 'scope. I don't think they are ever quite in sync (and in-phase). It's difficult to tell for sure. I suggest you try a function generator instead, if you have access to one.

 

[glossywhite]

Yes, I agree that a sound card is definitely NOT a precision gen - haha!

EDIT:

Using a 3.5mm to 3.5mm plug to plug lead, then to scope via 2 10x probes

 

[glossywhite]

Okay, so I had the "invert" mode on... oops - with invert off again, I get the single diag line when putting the same freq in both channels, but when putting the frequencies in that are listed in the OP, for the circle, the line re-appears...

 

[DerStrom8]

Yep, it seems to me two of your signals are equal frequency and in the same phase, but you have another mystery signal of the same frequency but 180 degrees out of phase. That's the only thing I can think of that would give you that X .

 

[DerStrom8]

Okay, so I had the "invert" mode on... oops - with invert off again, I get the single diag line when putting the same freq in both channels, but when putting the frequencies in that are listed in the OP, for the circle, the line re-appears...

Haha yup, that would explain the backwards diagonal line.

Still not sure why you're getting a diagonal line AND a rotating circle though. What are your scope knobs set to? (hint: A photo would be great here as well )

 

[glossywhite]

Haha yup, that would explain the backwards diagonal line.

Still not sure why you're getting a diagonal line AND a rotating circle though. What are your scope knobs set to? (hint: A photo would be great here as well )

Photo of settings (too large to embed)

https://farm3.staticflickr.com/2860/12215221613_718d626f95_o.jpg

 

[DerStrom8]

Out of curiosity, have you tried different channels?

 

[glossywhite]

Out of curiosity, have you tried different channels?

If I knew how to set this thing up, I'd do that. It's like a space shuttle

 

[DerStrom8]

If I knew how to set this thing up, I'd do that. It's like a space shuttle

Just plug the probes into channels 3 and 4 and turn them on instead of channels 1 and 2. It looks like the volts/div knobs are the same for channels 1&2 and 3&4 (an interesting setup, if that is the case), so you shouldn't have to adjust them.

 

[glossywhite]

Just plug the probes into channels 3 and 4 and turn them on instead of channels 1 and 2. It looks like the volts/div knobs are the same for channels 1&2 and 3&4 (an interesting setup, if that is the case), so you shouldn't have to adjust them.

As I said, it's like a space ship - I had no idea about CH3 and 4 - they're cryptic!

 

[DerStrom8]

As I said, it's like a space ship - I had no idea about CH3 and 4 - they're cryptic!

In that case before you continue I suggest you read up on oscilloscope controls

You can't use one effectively unless you know how it works. You'll have to trust me on this. Here's the manual, read parts 3-1 through 3-11:

Good luck!
Matt

 

[glossywhite]

In that case before you continue I suggest you read up on oscilloscope controls

You can't use one effectively unless you know how it works. You'll have to trust me on this. Here's the manual, read parts 3-1 through 3-11:

Good luck!
Matt

Thank you

 

[Reloadron]

Looking at your controls do you have Add selected in the vertical mode? If yes, turn add off and just use the X, Y mode.

Also, as suggested, you will need to get a handle on Oscilloscope Basics so the scope is no longer like the controls of a space shuttle.

Ron