Author Topic: Siglent SDG-2042x 10Mhz reference signal is bad  (Read 635 times)

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Offline john95

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Siglent SDG-2042x 10Mhz reference signal is bad
« on: May 16, 2019, 03:59:35 pm »
hi, I just bought a Siglent SDG-2042x , and use scope to check its 10mhz reference signal from its back. take a look at the photo. is it bad or normal? thanks.
 

Offline agehall

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #1 on: May 16, 2019, 05:27:43 pm »
Have you adjusted the compensation on the probes? That is typically what this reference is for...
 
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Offline radiolistener

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #2 on: May 16, 2019, 05:40:50 pm »
is it bad or normal? thanks.

looks very good. But you can't see it's jitter with such low resolution. Why you're think that it's bad?
« Last Edit: May 16, 2019, 05:45:23 pm by radiolistener »
 

Offline tautech

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #3 on: May 16, 2019, 08:00:19 pm »
hi, I just bought a Siglent SDG-2042x , and use scope to check its 10mhz MHz reference signal from its back. take a look at the photo. is it bad or normal? thanks.

Doesn't look anything like 10 mHz.  ;)

For comparison, SDG2042X NIB unit 10 MHz Ref Out > BNC cable > SDS1104X-E 1M input.




Into 50 Ohm termination before channel BNC




Now, this is a perfectly good reference clock not some square wave competition.
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Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #4 on: May 17, 2019, 03:00:49 am »
thanks for the answer. The reason I thought it was bad is because I expected it was a perfect sine wave. I remember I saw a youtube on SDG1032x, which was sending out perfect sine wave. It looks like this none sine wave waveform is correct for reference.
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #5 on: May 17, 2019, 03:05:06 am »
Thank you very much. You are always very helpful. I generated exactly the same waveforms as yours in both cases with and without 50 ohm adjustment. So it is correct signal generated. Nothing wrong with my SDG. Furthermore, I did SDG->BNC with alligator clip->OEM Keysight probe. The waveform is a bit different attached here.
 

Online pigrew

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #6 on: May 17, 2019, 03:26:40 am »
The wavyness of your measurement using a probe is due to bad impedance matching. Generally, I wouldn't use alligator clips above 1 MHz if you want good signal fidelity. Use a BNC cable instead, preferably with a 50 Ohm termination (if the source is 50 ohms). Or, you could cut a BNC cable, and probe the cable within a few cm of the 10 MHz output (it's the length of the line between the source and the mismatch that allows reflections to create large ripples; reducing the length will make the standing waves smaller). The first measurements looked much better.

The SDG2042X's datasheet claims its output is 50 ohm, with a 3.3Vpp amplitude into Hi-Z. Your oscilloscope (DSO-X 2012A) doesn't have a 50-ohm load, so you should provide an external termination by using an in-line feedthru terminator (like Thor T4119). This would be attached directly at the oscilloscope's input. The amplitude should be halved with the termination, to around 1.3Vpp.

The signals themselves look OK, but not great. You may be able to get a rough idea of the period-to-period jitter using your scope. Use the horizontal trigger/delay knob (top of the scope, small knob), to zoom into the rising edge AFTER the one where the scope trigger (so a delay of 100ns). Turn on infinite persistence mode and get a feel for the width of the acquired signal, which would be the peak-to-peak period variation of your source. Since your oscilloscope samples at 2 GSa/s, I'd expect you to be able to measure it with a precision around a few hundred picoseconds. You may be able to zoom into an edge much after the trigger edge (like 1 second later) to get an idea for the longer-term jitter, too, though the oscilloscope's timebase jitter may start to dominate. You can also do some measurements by using edge delay measurements, but you may have to zoom out enough that your sampling rate decreases too much. If you acquire the data onto a computer and interpolate between sample-points, I think you could get a quite good idea of the jitter's magnitude and make pretty plots.

Post your results for the jitter if you get a chance. It's not the most advanced way, but it should give you an idea of its performance.

Often square waves are desirable for clocks because the signal transitions more quickly through the logic theshold value. Close to the midpoint, a sine wave changes more slowly than a square wave would, which lets more jitter into the system. Many good quality oscillators are clipped sine-waves or square waves, for this reason.

EDIT: And now I'm looking into Keysight's N8900A software which would provide offline jitter analysis, but OMFG, it's a >3 GiB download and costs US$8500, and all I wanted is to look at the user manual.
« Last Edit: May 17, 2019, 03:37:57 am by pigrew »
 
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Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #7 on: May 17, 2019, 03:44:49 am »
Thank you very much for explanation. I will do the jitter measurement once I have time.
I did use BNC-BNC cable linking both machines and I got exactly the same result as Tautech posted in both with and without 50 ohm termination cases. I have a Rigol 50 ohm termination. I did some extra check on my HAM radio with the machine. Share video here, If you see anything wrong, or interesting, please let me know. Thanks.

HAM S meter meaning (practice):
Check  FM, AM performance:
DC volts on FM signal:
Siglent Signal Generator performance check:
HAM S meter meaning (theory): 

 
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Offline radiolistener

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #8 on: May 17, 2019, 05:30:49 am »
HAM S meter meaning (practice)

you're doing wrong calculation, note that you're connected sig gen to receiver input which is equivalent to 50 Ohm load. But your gen is set to HiZ load mode, it means that your gen shows voltage for unterminated line. But it is terminated with receiver input. So, the actual voltage on receiver input is a half of HiZ value shown on your sig  gen.

Just switch your sig gen to 50 Ohm load mode instead of HiZ to see correct voltage on receiver input.

Regarding to the S-level, you can calculate it with RFCALC (see attachment) from voltage, or from dBm power.
Also, note that there are two S-level scale versions - one for HF band and one for VHF/UHF band, they are different.
RFCALC can convert both versions of S-level versions to voltage and back.
« Last Edit: May 17, 2019, 05:47:17 am by radiolistener »
 
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Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #9 on: May 17, 2019, 05:35:10 am »
Thank you very much. Someone told me that earlier. I will retest. I thought it was on 50 ohm as default, and not sure why it was changed to HiZ. Thanks again for pointing it out.
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #10 on: May 17, 2019, 05:38:44 am »
do you have Mac or Linux version of RFCALC? or even web based? I have not used window machine for ages.
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #11 on: May 17, 2019, 05:40:30 am »
if the actual voltage reaching radio is half of what I thought. It means the power reaching HAM radio is 6 dbm (20 * log(2)) lower. it matches perfectly to the theoretical predication. Thanks. I will set to 50 ohm and retest.
 

Offline radiolistener

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #12 on: May 17, 2019, 05:49:33 am »
do you have Mac or Linux version of RFCALC? or even web based? I have not used window machine for ages.

it is written in C# and should run on Mac or Linux with no issues under mono.
Just install mono runtime and run it with command line:
Code: [Select]
mono RFCALC.exe
PS: be careful with transceiver, if you randomly press TX button on your transceiver, you can burn-out your sig gen output... ;)
« Last Edit: May 17, 2019, 06:02:06 am by radiolistener »
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #13 on: May 17, 2019, 05:55:30 am »
correct. I should be very very careful.
1) if I transmit from my HAM radio, it damages SDG.
2) if I accidentally output more power from SDG, I burn up HAM radio.

I should test as less as possible on this setup as the potential damage is severe. especially not after couple of drinks.

If proven correct because of this HiZ issue, I will be extremely happy that I worked out formula from basic assumption.
 

Offline radiolistener

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #14 on: May 17, 2019, 06:02:21 am »
Here is some values from RFCALC:
2 mVpp = -50 dBm = S9 + 23 dB
5 mVpp = -42.04 dBm = S9 + 30.96 dB
15 mVpp = -32.5 dBm = S9 + 40 dB
45 mVpp = -22.96 dBm = S9 + 50 dB
142 mVpp = -12.98 dBm = S9 + 60 dB
448 mVpp = -2.995 dBm = S9 + 70 dB
 

Offline radiolistener

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #15 on: May 17, 2019, 06:03:58 am »

2) if I accidentally output more power from SDG, I burn up HAM radio.

I think this signal generator is unable to burn up your radio, it's power too weak and almost equivalent to voltage from antenna near powerful transmitter. It should works ok with no overload up to 1-2 Vpp on the input.

And thanks for video with modulation mode demo.  :)
« Last Edit: May 17, 2019, 06:08:25 am by radiolistener »
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #16 on: May 17, 2019, 06:07:49 am »
thanks for the table. it matches my calculation exactly. for 50 ohm radio impedance, it is "Power(dbm) = 20 * log(mVpp) -56 ".
SDG can damage HAM. it can output 20 V p-p. and according to your table, 448 mvps might damage it already since S meter max is S9 + 60 db.
« Last Edit: May 17, 2019, 06:18:23 am by john95 »
 

Offline radiolistener

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #17 on: May 17, 2019, 06:11:57 am »
448 mvps might damage it already since S meter max is S9 + 60 db.

No, voltages up to 1-2 Vpp is normal. It can overload input and your S-meter will show max value, but it is not critical, because such voltage from antenna is a common case. You can apply such voltage directly to ADC with no issues. :)

You can enable internal attenuator in order to reduce signal level.

20 Vpp may be dangerous. I think this radio can survive it, but I don't recommed to apply more than 2 Vpp.
« Last Edit: May 17, 2019, 06:22:44 am by radiolistener »
 
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Offline tautech

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #18 on: May 17, 2019, 06:23:54 am »
Thank you very much. Someone told me that earlier. I will retest. I thought it was on 50 ohm as default, and not sure why it was changed to HiZ. Thanks again for pointing it out.
FYI the output impedance of all SDG's is only ever 50 Ohm.
When we change the output level between HiZ and 50 Ohm all we change is the max amplitude level so to match the selected/expected load impedance.
Max outputs:
HiZ = 20V p-p
50 Ohm = 10V p-p
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Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #19 on: May 17, 2019, 06:29:03 am »
Thank you very much. Someone told me that earlier. I will retest. I thought it was on 50 ohm as default, and not sure why it was changed to HiZ. Thanks again for pointing it out.
FYI the output impedance of all SDG's is only ever 50 Ohm.
When we change the output level between HiZ and 50 Ohm all we change is the max amplitude level so to match the selected/expected load impedance.
Max outputs:
HiZ = 20V p-p
50 Ohm = 10V p-p

thanks. 10 Vpp will damage my HAM radio's front end.
 

Offline tautech

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #20 on: May 17, 2019, 06:33:25 am »
Thank you very much. Someone told me that earlier. I will retest. I thought it was on 50 ohm as default, and not sure why it was changed to HiZ. Thanks again for pointing it out.
FYI the output impedance of all SDG's is only ever 50 Ohm.
When we change the output level between HiZ and 50 Ohm all we change is the max amplitude level so to match the selected/expected load impedance.
Max outputs:
HiZ = 20V p-p
50 Ohm = 10V p-p

thanks. 10 Vpp will damage my HAM radio's front end.
Yes of course but you 'the driver' are in control and make the output level adjustments to protect your DUT.  ;)
« Last Edit: May 17, 2019, 06:55:08 am by tautech »
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Offline radiolistener

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #21 on: May 17, 2019, 06:42:24 am »
thanks. 10 Vpp will damage my HAM radio's front end.

10 Vpp is 24 dBm, it may be dangerous for your radio. But you can connect 20 dB attenuator between sig gen and radio. It will reduce max level below 10 dBm, so you can use your gen with max level in safe way for your radio.

Also attenuator can reduce damage power for your sig gen output if you randomly press TX button on the transceiver. The chance that attenuator can save sig gen from TX mode is small (your radio can provide 100W = +50 dBm power, it's a lot), but at least it will reduce power, so damage may be more lightweight
« Last Edit: May 17, 2019, 06:57:40 am by radiolistener »
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #22 on: May 17, 2019, 05:11:13 pm »
The wavyness of your measurement using a probe is due to bad impedance matching. Generally, I wouldn't use alligator clips above 1 MHz if you want good signal fidelity. Use a BNC cable instead, preferably with a 50 Ohm termination (if the source is 50 ohms). Or, you could cut a BNC cable, and probe the cable within a few cm of the 10 MHz output (it's the length of the line between the source and the mismatch that allows reflections to create large ripples; reducing the length will make the standing waves smaller). The first measurements looked much better.

The SDG2042X's datasheet claims its output is 50 ohm, with a 3.3Vpp amplitude into Hi-Z. Your oscilloscope (DSO-X 2012A) doesn't have a 50-ohm load, so you should provide an external termination by using an in-line feedthru terminator (like Thor T4119). This would be attached directly at the oscilloscope's input. The amplitude should be halved with the termination, to around 1.3Vpp.

The signals themselves look OK, but not great. You may be able to get a rough idea of the period-to-period jitter using your scope. Use the horizontal trigger/delay knob (top of the scope, small knob), to zoom into the rising edge AFTER the one where the scope trigger (so a delay of 100ns). Turn on infinite persistence mode and get a feel for the width of the acquired signal, which would be the peak-to-peak period variation of your source. Since your oscilloscope samples at 2 GSa/s, I'd expect you to be able to measure it with a precision around a few hundred picoseconds. You may be able to zoom into an edge much after the trigger edge (like 1 second later) to get an idea for the longer-term jitter, too, though the oscilloscope's timebase jitter may start to dominate. You can also do some measurements by using edge delay measurements, but you may have to zoom out enough that your sampling rate decreases too much. If you acquire the data onto a computer and interpolate between sample-points, I think you could get a quite good idea of the jitter's magnitude and make pretty plots.

Post your results for the jitter if you get a chance. It's not the most advanced way, but it should give you an idea of its performance.

Often square waves are desirable for clocks because the signal transitions more quickly through the logic theshold value. Close to the midpoint, a sine wave changes more slowly than a square wave would, which lets more jitter into the system. Many good quality oscillators are clipped sine-waves or square waves, for this reason.

EDIT: And now I'm looking into Keysight's N8900A software which would provide offline jitter analysis, but OMFG, it's a >3 GiB download and costs US$8500, and all I wanted is to look at the user manual.

how to Turn on infinite persistence mode?
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #23 on: May 18, 2019, 04:50:09 am »
thank you everyone. After change SDG to 50 ohm load instead of HiZ, the HAM radio reports the same power as predicated (P(dbm) = 20 * log (Vmpp) - 56).
 

Offline john95

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Re: Siglent SDG-2042x 10Mhz reference signal is bad
« Reply #24 on: May 18, 2019, 04:30:21 pm »
The wavyness of your measurement using a probe is due to bad impedance matching. Generally, I wouldn't use alligator clips above 1 MHz if you want good signal fidelity. Use a BNC cable instead, preferably with a 50 Ohm termination (if the source is 50 ohms). Or, you could cut a BNC cable, and probe the cable within a few cm of the 10 MHz output (it's the length of the line between the source and the mismatch that allows reflections to create large ripples; reducing the length will make the standing waves smaller). The first measurements looked much better.

The SDG2042X's datasheet claims its output is 50 ohm, with a 3.3Vpp amplitude into Hi-Z. Your oscilloscope (DSO-X 2012A) doesn't have a 50-ohm load, so you should provide an external termination by using an in-line feedthru terminator (like Thor T4119). This would be attached directly at the oscilloscope's input. The amplitude should be halved with the termination, to around 1.3Vpp.

The signals themselves look OK, but not great. You may be able to get a rough idea of the period-to-period jitter using your scope. Use the horizontal trigger/delay knob (top of the scope, small knob), to zoom into the rising edge AFTER the one where the scope trigger (so a delay of 100ns). Turn on infinite persistence mode and get a feel for the width of the acquired signal, which would be the peak-to-peak period variation of your source. Since your oscilloscope samples at 2 GSa/s, I'd expect you to be able to measure it with a precision around a few hundred picoseconds. You may be able to zoom into an edge much after the trigger edge (like 1 second later) to get an idea for the longer-term jitter, too, though the oscilloscope's timebase jitter may start to dominate. You can also do some measurements by using edge delay measurements, but you may have to zoom out enough that your sampling rate decreases too much. If you acquire the data onto a computer and interpolate between sample-points, I think you could get a quite good idea of the jitter's magnitude and make pretty plots.

Post your results for the jitter if you get a chance. It's not the most advanced way, but it should give you an idea of its performance.

Often square waves are desirable for clocks because the signal transitions more quickly through the logic theshold value. Close to the midpoint, a sine wave changes more slowly than a square wave would, which lets more jitter into the system. Many good quality oscillators are clipped sine-waves or square waves, for this reason.

EDIT: And now I'm looking into Keysight's N8900A software which would provide offline jitter analysis, but OMFG, it's a >3 GiB download and costs US$8500, and all I wanted is to look at the user manual.

checked SDG2000X 10 MHz reference clock quality:
 


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