### Author Topic: Rigol dg1022u amplitude issue [solved]  (Read 2594 times)

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#### Damianos

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##### Re: Rigol dg1022u amplitude issue
« Reply #25 on: December 23, 2017, 09:39:25 pm »
If I understand correctly what you mean, no!

If you use a coaxial line (such as RG58 and BNC), you have to terminate it at its end, that is at the oscilloscope input. The resistor must be equal to characteristic impedance of the line, that is 50 Ohms.

The probe (the 10:1) has inside a resistor in series and makes a divider with the input resistance of the oscilloscope. But, because there is also a capacitance there, it has also a trimming capacitor to compensate for that. If the compensation is not correctly adjusted, then the division depends on the frequency. A proper adjustment minimizes capacitive loading.

Avoid to use the grounding wire of the probe, remove it. If the probe has a BNC adaptor, use it. If not, try to attach the probe on the connector of the generator directly; in this case the "spring component" of the probe may help to connect the ground.

Performing the sweep experiment, which I suggested earlier, can find out if the problem is generated by wiring or something else.

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##### Re: Rigol dg1022u amplitude issue
« Reply #26 on: December 23, 2017, 09:51:04 pm »
If I understand correctly what you mean, no!

If you use a coaxial line (such as RG58 and BNC), you have to terminate it at its end, that is at the oscilloscope input. The resistor must be equal to characteristic impedance of the line, that is 50 Ohms.

The probe (the 10:1) has inside a resistor in series and makes a divider with the input resistance of the oscilloscope. But, because there is also a capacitance there, it has also a trimming capacitor to compensate for that. If the compensation is not correctly adjusted, then the division depends on the frequency. A proper adjustment minimizes capacitive loading.

Avoid to use the grounding wire of the probe, remove it. If the probe has a BNC adaptor, use it. If not, try to attach the probe on the connector of the generator directly; in this case the "spring component" of the probe may help to connect the ground.

Performing the sweep experiment, which I suggested earlier, can find out if the problem is generated by wiring or something else.

My english is not very well ahah another mistale due to my cheap english..I mean to terminate with a resistor (50 or 1M) at the bnc side with a resistor, and it worked! The problem with the probe was the compensation..that was causing all this problems

I thank you all for the patient with me..but for me there are some language barrior..specially thank you for the suggestion! Compensation..argh..

#### Damianos

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #27 on: December 23, 2017, 09:58:56 pm »
I'm glad if I helped even a little, but more because there is no problem/damage to any of your devices!

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #28 on: December 23, 2017, 10:02:18 pm »
I'm glad if I helped even a little, but more because there is no problem/damage to any of your devices!

Again, thank you very much!

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #29 on: December 24, 2017, 01:38:24 am »
So much ladened with confused theory, I just wonder how you are going to do troubleshooting field measurements when the point you want to probe at is of "unknown" impedance?

Theories sounded like textbook I must say, yeah!

Practically dumpfounded - How much voltage drop will you encounter if DG1022U is at high impedance, 10Vpp, sine wave at 25Mhz, and the oscilloscope is set to 1Megohm input impedance over the RG58 - BNC to BNC cable of length 2m? [knowing that the characteristic impedance of the RG58 cable is 50 ohms]. ?

With that findings, you build onto your foundation only to move forward.

Cheers;

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #30 on: December 24, 2017, 07:46:37 am »
So much ladened with confused theory, I just wonder how you are going to do troubleshooting field measurements when the point you want to probe at is of "unknown" impedance?

Theories sounded like textbook I must say, yeah!

Practically dumpfounded - How much voltage drop will you encounter if DG1022U is at high impedance, 10Vpp, sine wave at 25Mhz, and the oscilloscope is set to 1Megohm input impedance over the RG58 - BNC to BNC cable of length 2m? [knowing that the characteristic impedance of the RG58 cable is 50 ohms]. ?

With that findings, you build onto your foundation only to move forward.

Cheers;

If I have HighZ on the output of the F.G and HigZ on the input of the oscilloscope, they are matched, and there will no drop, cause the F.G adjust it self to a proper level, due to the set of the inpedance

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #31 on: December 24, 2017, 07:54:00 am »
https://imageshack.us/i/pme051OBj = photo of the connections (I don't have a probe to bnc adapter)

https://imageshack.us/i/pmGhcSVhj = settings on the Rigol dg1022U

https://imageshack.us/i/pmrMaFV7j = scope measuraments

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #32 on: December 24, 2017, 10:03:20 am »
BNC to BNC means you do not use the Probe. Connect directly from FG to scope.
You know why Rigol include a BNC to BNC connector cable for you? It's not to make funny terminating resistors, definitely.

From the photo, You still do not have the cable?

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #33 on: December 24, 2017, 11:09:48 am »
BNC to BNC means you do not use the Probe. Connect directly from FG to scope.
You know why Rigol include a BNC to BNC connector cable for you? It's not to make funny terminating resistors, definitely.

From the photo, You still do not have the cable?

It's incorrect hooking the F.G to the Scope without a termination, that the scope doesn't have
You will have amplitude issue, or phase shift

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #34 on: December 24, 2017, 11:14:58 am »
And as Damianos says, a 1:1 connection (bnc to bnc) is wrong in this case

#### Damianos

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #35 on: December 24, 2017, 11:37:21 am »
So much ladened with confused theory, I just wonder how you are going to do troubleshooting field measurements when the point you want to probe at is of "unknown" impedance?

Theories sounded like textbook I must say, yeah!

Practically dumpfounded - How much voltage drop will you encounter if DG1022U is at high impedance, 10Vpp, sine wave at 25Mhz, and the oscilloscope is set to 1Megohm input impedance over the RG58 - BNC to BNC cable of length 2m? [knowing that the characteristic impedance of the RG58 cable is 50 ohms]. ?

With that findings, you build onto your foundation only to move forward.

Cheers;
It seems that you have confused a little. Here are discussed only simple and practical things.

To answer your question, I will try to explain some simple things:
- The output amplifier, of a typical function generator, has a very low output impedance. For practical reasons there is a resistor connected in series from it to the output connector. This resistor, almost always, has a value of 50 Ohms. This means that when any load is connected at the connector it is created a voltage divider with the upper resistor having this 50 Ohms value. The setting of the load impedance, on the generator, simply adjusts the amplitude of the amplifier to have on the load the "requested" value. It does nothing else.
- To simplify things about the transmission line (the RG58 cable): when it is terminated with a "pure resistance" equal to its characteristic value, then this resistance is "reflected" to the input. Anything else produces disturbances that need a little physics and mathematics to analyze them... (search for forward/reflected/standing waves on transmission lines). Also, have a look at the other specifications of the RG58, such as capacitance/resistance/inductance per length unit.
- It is already described a little the voltage divider of the probe...
- It is also proposed an experiment by sweeping the frequency... (even if the mentioned length of the line seems that is short relative to the wavelength, around 1/8, it can reveal some disturbances)
If you separate each one of the above, you will see that they are not a "mountain" but simple things...

In conclusion: you have to transfer the signal with a transmission line, up to a point and then measure it with a high-impedance probe. In accordance with the above, terminate the line with a suitable resistor and connect the properly adjusted probe on this resistance.

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##### Re: Rigol dg1022u amplitude issue [solved]
« Reply #36 on: December 24, 2017, 11:53:27 am »
So much ladened with confused theory, I just wonder how you are going to do troubleshooting field measurements when the point you want to probe at is of "unknown" impedance?

Theories sounded like textbook I must say, yeah!

Practically dumpfounded - How much voltage drop will you encounter if DG1022U is at high impedance, 10Vpp, sine wave at 25Mhz, and the oscilloscope is set to 1Megohm input impedance over the RG58 - BNC to BNC cable of length 2m? [knowing that the characteristic impedance of the RG58 cable is 50 ohms]. ?

With that findings, you build onto your foundation only to move forward.

Cheers;
It seems that you have confused a little. Here are discussed only simple and practical things.

To answer your question, I will try to explain some simple things:
- The output amplifier, of a typical function generator, has a very low output impedance. For practical reasons there is a resistor connected in series from it to the output connector. This resistor, almost always, has a value of 50 Ohms. This means that when any load is connected at the connector it is created a voltage divider with the upper resistor having this 50 Ohms value. The setting of the load impedance, on the generator, simply adjusts the amplitude of the amplifier to have on the load the "requested" value. It does nothing else.
- To simplify things about the transmission line (the RG58 cable): when it is terminated with a "pure resistance" equal to its characteristic value, then this resistance is "reflected" to the input. Anything else produces disturbances that need a little physics and mathematics to analyze them... (search for forward/reflected/standing waves on transmission lines). Also, have a look at the other specifications of the RG58, such as capacitance/resistance/inductance per length unit.
- It is already described a little the voltage divider of the probe...
- It is also proposed an experiment by sweeping the frequency... (even if the mentioned length of the line seems that is short relative to the wavelength, around 1/8, it can reveal some disturbances)
If you separate each one of the above, you will see that they are not a "mountain" but simple things...

In conclusion: you have to transfer the signal with a transmission line, up to a point and then measure it with a high-impedance probe. In accordance with the above, terminate the line with a suitable resistor and connect the properly adjusted probe on this resistance.

Nobody would explain that better than this

Smf