Can Your DSO Do This?

[nctnico]

On a DSO an alt triggering mode is of very little use because the signals will need to be sampled independantly which make the 2 traces unrelated in time. IOW: you won't be able to see how a single glitch on channel 1 affects the signal showed in channel 2. The strong point of a DSO is that all channes are sampled synchronously and each channel shows the result from the same circumstances (the signals have a perfect time relation).

I do have to note that I have heard about certain (older) Tektronix DSOs which using alternate sampling so they can show unrelated signals as well.

[Wuerstchenhund]

On a DSO an alt triggering mode is of very little use because the signals will need to be sampled independantly which make the 2 traces unrelated in time. IOW: you won't be able to see how a single glitch on channel 1 affects the signal showed in channel 2. The strong point of a DSO is that all channes are sampled synchronously and each channel shows the result from the same circumstances (the signals have a perfect time relation).

I do have to note that I have heard about certain (older) Tektronix DSOs which using alternate sampling so they can show unrelated signals as well.

I'm still not sure what the real-world value of Alt Trigger is. Usually when looking at multiple signals at once they are all time-related in some way (which is usually the reason why you'd want to have them together on the screen in the first place).

I'd be curious in which situations Alt Trg was of value. My guess is that there aren't many.

[nctnico]

I can imagine it may be handy to have 2 time unrelated signals stable on screen for some tests.

BTW: On the Tektronix scopes I mention earlier the alternate sampling had the unwanted side effect that timing relation between signals wasn't there which confused the hell out of unsuspected users especially since this wasn't documenten. Free_electron knows more details since he brought it up a long time ago.

[CustomEngineerer]

When I first purchased a scope I made the mistake of getting the Hantek MSO5102D. It had an "Alternative Trigger" that allowed you to alternate triggering off of channels 1 & 2. I played around with the Alternative Trigger a bit but ended up returning the scope because of constant lock ups. I ended up getting a Rigol DS2072A instead. When I first got the Rigol I was a little disappointed that it didn't have an equivalent trigger type, but I have yet to run into a situation where I actually need it.

[vk6zgo]

On a DSO an alt triggering mode is of very little use because the signals will need to be sampled independantly which make the 2 traces unrelated in time. IOW: you won't be able to see how a single glitch on channel 1 affects the signal showed in channel 2. The strong point of a DSO is that all channes are sampled synchronously and each channel shows the result from the same circumstances (the signals have a perfect time relation).

I do have to note that I have heard about certain (older) Tektronix DSOs which using alternate sampling so they can show unrelated signals as well.

I'm still not sure what the real-world value of Alt Trigger is. Usually when looking at multiple signals at once they are all time-related in some way (which is usually the reason why you'd want to have them together on the screen in the first place).

I'd be curious in which situations Alt Trg was of value. My guess is that there aren't many.

I've never had occasion to use it.
All the possibilities I try to think of all fail the "why would you need to do that" test.

[Smokey]

Didn't single shot mode and deep memory on DSOs effectively make all this obsolete? 

[alsetalokin4017]

Why build it in to an analog (or digital) scope if it's not useful?   

Just because you or I can't think of situations where it would be useful, doesn't mean that there aren't any. And those situations must come up often enough so that even a "beginner" 2-trace analog scope like the Tek 2213 series had Vertical Mode triggering designed in.

[vk6zgo]

I was thinking,perhaps to look at a gated signal,where that signal isn't synched to the gating frequency.

One case would be a Morse Code letter keying an RF carrier.

Attack & decay time of the envelope may do strange things to the first few cycles of the RF envelope,which would be interesting to know,as they would indicate if the RF cycle was likely to produce spurii.

Another,I guess,would be plain old AM,where you might want took at phase changes in the RF with modulation.

I'm not sure that either would be that easy to do,& there are other ways to look at them.
For instance,with Morse keying,as long as the envelops shape is OK,the generation of spurii is minimised.

[Wuerstchenhund]

Why build it in to an analog (or digital) scope if it's not useful?   

Who knows, maybe because technology back then was different than it is today, and with that the type of signal that most engineers had to deal with. Today digital stuff is almost everywhere and in digital systems signals are usually time-related, which often wasn't the case in analog systems.

Just because you or I can't think of situations where it would be useful, doesn't mean that there aren't any.

Which is exactly the reason why I asked for any real-life examples...

[Smokey]

Just because you or I can't think of situations where it would be useful, doesn't mean that there aren't any.

Which is exactly the reason why I asked for any real-life examples...

Gives people something to talk about on the internet...

[miguelvp]

Couldn't the DS2000 and DS1000z do that with the Delay trigger type?

[vk6zgo]

Analog TV was all time related,(except the actual RF channels in most places except France,where they locked the vision & sound carriers to line syncs).
As I did a lot of my "scoping" on TV related stuff,I didn't need to use this function.

[markone]

My spanking new GDS-2072E does :

[nctnico]

Cool! I have seen the alternate option on mine as well but until now had no clue what is was for but I'll admit I did not bother to look it up in the manual. Let's give it a try with 4 channels...

[Fungus]

Didn't single shot mode and deep memory on DSOs effectively make all this obsolete?

Nope. Simultaneously watching two different signals with low frequency modulators is awesome 

(dude!)

[C]

Oscilloscope

is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time.

If you use the same probe to look at a reference signal and then switch the probe to look at a second signal, the differences you see will be the signal differences.

The Oscilloscope does not even have to be in calibration for this.

A smart user of the scope would use the UN-cal Volts/div knob & the UN-cal sweep time knob to set the reference signal to be an easy to look at and check on the display.

Having more than one channel and or scope that you can use, just reduces the number of setting changes needed.

Some adjustments can effect more than one signal. Having more inputs saves time if you have to adjust a signal that also effects a previous signal in some way.

A system that uses many matching signal channels each with many test points per channel that have to be correct.

A simple case is a 14 channel reel to reel tape recorder. A nice one where you have separate record and playback heads. After you have one recorder working, you then need to get the ability to swap tapes between recorders.
With just 8 recorders that is 112 signals to match up per test point.

The tape heads do wear which causes signal changes. So for a final result you want record input= tape = playback output.

For those of you who have worked with something like this, add two little things.
Reduce the designed  recording speed by 1/2 and switch to very thin tape with out losing needed BW.
14" glass reels with I think it was 6000 feet of tape.

The recorders I am thinking of were $200,000 in the early 1970's before the changes needed for 1/2 speed and thin tape. One of a pair was always running 24x360, with the 360 often increased.

[Bryan]

My older DS1052E has alternate triggering. Surprised the newer DS1047 doesn't

[alsetalokin4017]

Couldn't the DS2000 and DS1000z do that with the Delay trigger type?

Not as far as I can tell. If you can get a 1000z to do it, please post your technique and results.

[alsetalokin4017]

Oscilloscope

is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time.

If you use the same probe to look at a reference signal and then switch the probe to look at a second signal, the differences you see will be the signal differences.

The Oscilloscope does not even have to be in calibration for this.

A smart user of the scope would use the UN-cal Volts/div knob & the UN-cal sweep time knob to set the reference signal to be an easy to look at and check on the display.

Having more than one channel and or scope that you can use, just reduces the number of setting changes needed.

Some adjustments can effect more than one signal. Having more inputs saves time if you have to adjust a signal that also effects a previous signal in some way.

A system that uses many matching signal channels each with many test points per channel that have to be correct.

A simple case is a 14 channel reel to reel tape recorder. A nice one where you have separate record and playback heads. After you have one recorder working, you then need to get the ability to swap tapes between recorders.
With just 8 recorders that is 112 signals to match up per test point.

The tape heads do wear which causes signal changes. So for a final result you want record input= tape = playback output.

For those of you who have worked with something like this, add two little things.
Reduce the designed  recording speed by 1/2 and switch to very thin tape with out losing needed BW.
14" glass reels with I think it was 6000 feet of tape.

The recorders I am thinking of were $200,000 in the early 1970's before the changes needed for 1/2 speed and thin tape. One of a pair was always running 24x360, with the 360 often increased.

What? How is this relevant to the present question, which involves displaying two or more frequencies stably at the same time?

[alsetalokin4017]

Cool! I have seen the alternate option on mine as well but until now had no clue what is was for but I'll admit I did not bother to look it up in the manual. Let's give it a try with 4 channels...

That looks great!  Now I'm _really_ jealous...   

[miguelvp]

Couldn't the DS2000 and DS1000z do that with the Delay trigger type?

Not as far as I can tell. If you can get a 1000z to do it, please post your technique and results.

Not too stable and only had a little play with it. I don't have a DS1000z but it also has Delay trigger.

But as I said, sometimes it looses lock, but didn't play with all of the comparison types and values.

I used the same frequencies as markone's first image. 1MHz and 775KHz and this is the result on my DS2000 series:


Note: looking at the DS1000z programmer manual, the Trigger type Delay only works with two signals as well, so no alt on 4 channels, sorry. But you can choose two of all four channels.

Edit: But it's tricky to get the right Time value to get both channels in sync.

Edit2: maybe the less than greater than, or greater than less than will work best, they have an upper and lower time limit.

[miguelvp]

Explanation of the Delay Type options on the DS1000z (Edit, it should be similar for the DS2000) according to the programmer reference manual (after correcting some minor misspellings):

> GREater: trigger when the time difference (Delta T) between the specified edges of trigger source A and trigger source B is greater than the preset time limit.

< LESS: trigger when the time difference (Delta T) between the specified edges of trigger source A and trigger source B is lower than the preset time limit.

>< GLESs: trigger when the time difference (Delta T) between the specified edges of trigger source A and trigger source B is greater than the lower limit of the preset time and lower than the upper limit of the preset time. Note that the time lower limit must be lower than the time upper limit.

<> GOUT: trigger when the time difference (Delta T) between the specified edges of trigger source A and trigger source B is lower than the lower limit of the preset time or greater than the upper limit of the preset time. Note that the time lower limit must be lower than the time upper limit.

I think I got the symbols right

Edit: left the sweep on Auto and didn't change the holdoff value, maybe those can help too.
Also this is more cumbersome than just pressing the ALT button or CHOP like I have on my two Tek scopes and I can get 4 channels on those.
But I really never had the need to do an ALT because then you don't see the signal in relation to the other signal.
At least the Delay Trigger puts them in relation with each other, which might be more useful.

[alsetalokin4017]

Well... shiver me timbers, it worked!   Thanks, friends. The first times I tried it I didn't have faith, I guess, because I couldn't get it to work. But with the knowledge that it _could_ be done, I was able to get the settings right (for similar frequencies as used above).   


ETA:  I think I've got the hang of it now... Thanks again!

[miguelvp]

Now try with not being on STOP mode, it should work too

[alsetalokin4017]

Now try with not being on STOP mode, it should work too

Of course, I just use "STOP" so that saves to the USB will go faster. It's not necessary to have the scope Stopped to have the stable signals, but it sure does make screensaves a lot faster, especially when there are lots of things going on in the display.