Author Topic: DS1052E hacked to DS1102E waveform comparision  (Read 15134 times)

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alm

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #25 on: April 25, 2011, 09:09:20 pm »
The frequency specs for both the Tek & Rigol scopes would normally be for the unit itself,with any probe effects being additional to that.
Last time I checked, Tek specs usually stated that the performance specs are for the scope set to 50 ohms, but are typically also valid on the 1Mohm setting with the standard probes. Agilent and Tek work hard to deliver their performance at the probe tip, since that's the only thing that counts in the end. Not so sure about Rigol.

I agree that to test just the scope, a terminated transmission line connected directly to the input is the way to go.
 

Offline vk6zgo

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #26 on: April 26, 2011, 02:37:21 am »
Even when using the probe,a buffer would be useful,so the probe doesn't affect the output waveform from the IC.
The low Z output can be terminated directly,& the probe bridged across the termination.

Cheers,VK6ZGO
 

Offline Leo Bodnar

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #27 on: April 26, 2011, 08:50:06 am »
Just a short notice - [untapped] transmission line properly terminated only at the driving end would perform just as well as terminated at both. 
There will be massive reflection off the unterminated scope 1MOhm side but it should be absorbed by the driver.

Last time I checked, Tek specs usually stated that the performance specs are for the scope set to 50 ohms, but are typically also valid on the 1Mohm setting with the standard probes. Agilent and Tek work hard to deliver their performance at the probe tip, since that's the only thing that counts in the end. Not so sure about Rigol.
I agree that to test just the scope, a terminated transmission line connected directly to the input is the way to go.

Offline scrat

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #28 on: April 27, 2011, 01:59:44 am »
Just a short notice - [untapped] transmission line properly terminated only at the driving end would perform just as well as terminated at both. 
There will be massive reflection off the unterminated scope 1MOhm side but it should be absorbed by the driver.

Why? Reflection should be visible (since you're looking at the high-Z side), and make the response difficult to understand...
One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man. - Elbert Hubbard
 

Offline Leo Bodnar

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #29 on: May 20, 2011, 11:29:03 pm »
Just a short notice - [untapped] transmission line properly terminated only at the driving end would perform just as well as terminated at both. 
There will be massive reflection off the unterminated scope 1MOhm side but it should be absorbed by the driver.

Why? Reflection should be visible (since you're looking at the high-Z side), and make the response difficult to understand...

Reflection of what?  If the driver has matched impedance it won't re-reflect arriving pulse/front.

Offline scrat

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #30 on: May 23, 2011, 07:40:32 pm »
Just a short notice - [untapped] transmission line properly terminated only at the driving end would perform just as well as terminated at both. 
There will be massive reflection off the unterminated scope 1MOhm side but it should be absorbed by the driver.

Look above, you were speaking about reflection that should be absorbed by the driver. I gave the sentence "transmission line properly terminated only at the driving end" the meaning of a line having Z characteristic impedance fed by a Z impedance source, and 1MOhm at the other end. That should cause reflections to happen.
One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man. - Elbert Hubbard
 

Offline vk6zgo

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #31 on: May 24, 2011, 01:19:25 am »
At the Oscilloscope end you will probably only see a higher level signal  than if it is terminated both ends.At least this has been my experience with video signals.

Of course with video signals,the signal amplitude in volts is an important specification,so an unterminated connection may cause problems to the devices further down the line.

If you monitor the signal at the generator end with another oscilloscope,you will start to see strange effects if the cable to the unterminated oscilloscope is 1/4 wavelength,(or some multiple of 1/4 wave) at one of the frequency components of the signal.


VK6ZGO
 

Offline Leo Bodnar

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #32 on: May 24, 2011, 01:29:45 am »
Just a short notice - [untapped] transmission line properly terminated only at the driving end would perform just as well as terminated at both. 
There will be massive reflection off the unterminated scope 1MOhm side but it should be absorbed by the driver.

Look above, you were speaking about reflection that should be absorbed by the driver. I gave the sentence "transmission line properly terminated only at the driving end" the meaning of a line having Z characteristic impedance fed by a Z impedance source, and 1MOhm at the other end. That should cause reflections to happen.
Yes, there will be reflection going back to driver that will be absorbed in full if the Z-Z match is accurate.  The receiver won't see any reflection.

Offline scrat

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #33 on: May 24, 2011, 05:55:11 am »
Just a short notice - [untapped] transmission line properly terminated only at the driving end would perform just as well as terminated at both. 
There will be massive reflection off the unterminated scope 1MOhm side but it should be absorbed by the driver.

Look above, you were speaking about reflection that should be absorbed by the driver. I gave the sentence "transmission line properly terminated only at the driving end" the meaning of a line having Z characteristic impedance fed by a Z impedance source, and 1MOhm at the other end. That should cause reflections to happen.
Yes, there will be reflection going back to driver that will be absorbed in full if the Z-Z match is accurate.  The receiver won't see any reflection.

Reflections are completely damped only in the case of both ends adapted. Otherwise, high frequency stubs in transmission lines won't work, for example.
That's one way (IIRC) to estimate the distance at which a cable is broken.
One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man. - Elbert Hubbard
 

Offline jahonen

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #34 on: May 24, 2011, 06:04:59 am »
Yes it does work, like Leo described it. How the series termination (in point-to-point case) would otherwise work? One needs both ends terminated only if matching must be perfect from both directions, or the line is tapped (multipoint case).

There is 100% reflection from the mismatched load end, but since reflected and incident wave are in same phase at the end of the line, it does not cause any problem. Reflected wave then travels back to the source end, but there is no reflection from source end, since it is matched. Thus load does not see any kind of mismatch. Situation becomes completely different if signal is measured somewhere along the line, where the reflection is seen.

TDR measures reflections at the source end, where the reflection can be seen. It is consistent behavior with above description. I use same behavior to tune the series termination resistor, by adjusting the series termination resistor value so that the plateau becomes half of the final voltage (Zs+Rs=Z0).

Regards,
Janne
 

Offline scrat

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #35 on: May 24, 2011, 07:27:39 am »
Sorry, I was wrong!
At the return to the driver end the situation reaches its equilibrium, so no further reflections, as explained.
One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man. - Elbert Hubbard
 

Offline vk6zgo

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Re: DS1052E hacked to DS1102E waveform comparision
« Reply #36 on: May 24, 2011, 03:26:54 pm »
It is,of course,still best practice to terminate at the receiving end,especially if substantial power is being
transmitted through the cable,as operating at high SWR causes both voltage & current peaks at different points along the line,which may ,in a flexible coaxial cable, cause unwanted losses.

VK6ZGO

 


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