Siglent SDG-2042x 10Mhz reference signal is bad - Page 1
Forum section: electronics / beginners

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 05:59:35 am
content: 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.

author: agehall
author_rank: Frequent Contributor
timestamp: May 16, 2019, 07:27:43 am
content: Have you adjusted the compensation on the probes? That is typically what this reference is for...

author: radiolistener
author_rank: Super Contributor
timestamp: May 16, 2019, 07:40:50 am
content: Quote from: john95 on May 16, 2019, 05:59:35 amlooks very good. But you can't see it's jitter with such low resolution. Why you're think that it's bad?

author: tautech
author_rank: Super Contributor
timestamp: May 16, 2019, 10:00:19 am
content: Quote from: john95 on May 16, 2019, 05:59:35 amDoesn'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 BNCNow, this is a perfectly good reference clock not some square wave competition.

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 05:00:49 pm
content: 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.

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 05:05:06 pm
content: 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.

author: pigrew
author_rank: Frequent Contributor
timestamp: May 16, 2019, 05:26:40 pm
content: 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.

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 05:44:49 pm
content: 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):

author: radiolistener
author_rank: Super Contributor
timestamp: May 16, 2019, 07:30:49 pm
content: Quote from: john95 on May 16, 2019, 05:44:49 pmyou'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.

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 07:35:10 pm
content: 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.

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 07:38:44 pm
content: do you have Mac or Linux version of RFCALC? or even web based? I have not used window machine for ages.

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 07:40:30 pm
content: 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.

author: radiolistener
author_rank: Super Contributor
timestamp: May 16, 2019, 07:49:33 pm
content: Quote from: john95 on May 16, 2019, 07:38:44 pmit is written in C# and should run on Mac or Linux with no issues under mono.Justinstall mono runtimeand run it with command line:Code:mono RFCALC.exePS: be careful with transceiver, if you randomly press TX button on your transceiver, you can burn-out your sig gen output...

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 07:55:30 pm
content: 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.

author: radiolistener
author_rank: Super Contributor
timestamp: May 16, 2019, 08:02:21 pm
content: Here is some values from RFCALC:2 mVpp = -50 dBm = S9 + 23 dB5 mVpp = -42.04 dBm = S9 + 30.96 dB15 mVpp = -32.5 dBm = S9 + 40 dB45 mVpp = -22.96 dBm = S9 + 50 dB142 mVpp = -12.98 dBm = S9 + 60 dB448 mVpp = -2.995 dBm = S9 + 70 dB

author: radiolistener
author_rank: Super Contributor
timestamp: May 16, 2019, 08:03:58 pm
content: Quote from: john95 on May 16, 2019, 07:55:30 pmI 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.

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 08:07:49 pm
content: 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.

author: radiolistener
author_rank: Super Contributor
timestamp: May 16, 2019, 08:11:57 pm
content: Quote from: john95 on May 16, 2019, 08:07:49 pmNo, 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.

author: tautech
author_rank: Super Contributor
timestamp: May 16, 2019, 08:23:54 pm
content: Quote from: john95 on May 16, 2019, 07:35:10 pmFYI 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-p50 Ohm = 10V p-p

author: john95
author_rank: Contributor
timestamp: May 16, 2019, 08:29:03 pm
content: Quote from: tautech on May 16, 2019, 08:23:54 pmthanks. 10 Vpp will damage my HAM radio's front end.

author: tautech
author_rank: Super Contributor
timestamp: May 16, 2019, 08:33:25 pm
content: Quote from: john95 on May 16, 2019, 08:29:03 pmYes of course but you 'the driver' are in control and make the output level adjustments to protect your DUT.

author: radiolistener
author_rank: Super Contributor
timestamp: May 16, 2019, 08:42:24 pm
content: Quote from: john95 on May 16, 2019, 08:29:03 pm10 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

author: john95
author_rank: Contributor
timestamp: May 17, 2019, 07:11:13 am
content: Quote from: pigrew on May 16, 2019, 05:26:40 pmhow to Turn on infinite persistence mode?

author: john95
author_rank: Contributor
timestamp: May 17, 2019, 06:50:09 pm
content: 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).

author: john95
author_rank: Contributor
timestamp: May 18, 2019, 06:30:21 am
content: Quote from: pigrew on May 16, 2019, 05:26:40 pmchecked SDG2000X 10 MHz reference clock quality:

author: pigrew
author_rank: Frequent Contributor
timestamp: May 18, 2019, 06:59:29 pm
content: Quote from: john95 on May 18, 2019, 06:30:21 amYeah, that looks to be about the limit of your scope's internal measurement. One small tip is that you can change the soft-menu selection by pressing the soft-key multiple times (instead of going to the multi-function knob). Also, it likely has a statistics display for measurements (from the measure menu), so you can see, for example, the calculated standard deviation of the period. You scope may also have a zoom mode which lets you see the detail better.I repeated the measurement with a Tek 784D (4GSa/s), and it also seems to be close to the noise floor of the equipment. When directly using the BNC cable between the instruments, the rise time is increased by capacitive loading, allowing the vertical noise of the ADC to dominate the measurement's noise. With an active probe (<1pF) and a short cable, a sharp edge appears at the start of each edge, and then it slows down. I got the lowest jitter numbers by triggering on this small edge (at -1.1V). Be aware that RG-58 coax has about 25 pF/ft, so it will load the output quite a bit. The SDG2042X has a very weak output buffer. Most instruments will trigger at the midpoint of the signal (0V), so will be effected by higher jitter than I'm reporting (because of the lower slope at the midpoint).I got a one-cycle peak-to-peak of185psand a standard deviation of28ps. This is pretty much the noise floor of my oscilloscope, so the output likely has lower cycle-to-cycle jitter than this.The oscilloscope had a large enough jitter set to have an 1 second (a few ns pk-pk) that I wouldn't trust it so much to directly measure the 1 second jitter. As a different measurement, I used a Racal 1992 counter to test the 10 MHz output. I set the "period" with a 1 second gate hake a pk-pk of about 0.4 fs. Multiplying by 10^7 yields a pk-pk jitter of4ns pk-pkover one second. I have reasonably good confidence in this measurement since when using the counter to measure a separate OCXO 10 MHz reference, the last digit was holding steady.These do not directly translate to the output waveform's jitter since the generator's clock is clocked by a PLL, which could remove some of the high-frequency jitter.A more accurate measurement would be to use the oscilloscope to measure the phase shift between the SDG2042X and a reference clock (running at some even multiple of 100ns). The oscilloscope can sample this every second, so you can get precise measurement of the long-term jitter. The oscilloscope's resolution is <100ps, so the limiting factor is the reference clock. Note that two SDG2042X could be compared against eachother, which removes the influence of a reference clock. This sort of measurement is what a time-interval-counter does (I've been thinking about buying a TAPR TICC board (or making my own design) to do measurements like this). My counter has a single-shot resolution of only 1 ns whereas the TARP TICC measured with about 30 ps resolution. The data can then be used to calculate Allen deviation plots.

author: john95
author_rank: Contributor
timestamp: May 18, 2019, 07:16:35 pm
content: thanks for detailed explanation.