Siglent SDG2042X Low Frequency Limitations and Linearity - Page 1
Forum section: electronics / beginners

author: Peter_O
author_rank: Frequent Contributor
timestamp: December 13, 2020, 01:16:28 pm
content: (Hi there, great forum! I've been reading some time and learning a lot, today this is my first post.)I've go a Siglent SDG 2042X Generator.Use the ramp waveform to generate a sawtooth signal (highLevel -2V, lowLevel 2V, symmetry 100%)With a Siglent SDS 1202X-E Oscilloscpe:Above 50Hz everything seems to be fine. (addet screenshot 50Hz)Below 50Hz- the raising slope is increasingly nonlinear. (addet screenshot 5Hz)- the signal gets an increasing negative offset. (see same screenshot)Connection is a RG 58 BNC cable straight from out to input.1) Is this normal and to be expected?2) Why?3) Spec limits of Function-Generator?4) Beginner's error?

author: radiolistener
author_rank: Super Contributor
timestamp: December 13, 2020, 02:15:12 pm
content: I have the same behavior for AC coupling. At 20 Hz it looks like curve.Could you please show 100 Hz square wave with DC coupling?Here is how it looks on my scope:

author: radiolistener
author_rank: Super Contributor
timestamp: December 13, 2020, 02:30:15 pm
content: here is 5 Hz ramp with AC and DC coupling on my scope:

author: Peter_O
author_rank: Frequent Contributor
timestamp: December 13, 2020, 03:08:03 pm
content: Quote from: PeDre on December 13, 2020, 01:43:56 pmHmm. Theoretically this should have been clear to me. Practically it was not.Works fine now.So it was 4) Beginner's error. :-)Hoped for that.Thx a lot Peter for the quick reply.

author: radiolistener
author_rank: Super Contributor
timestamp: December 13, 2020, 04:45:38 pm
content: Quote from: Peter_O on December 13, 2020, 03:08:03 pmCould you please show 100 Hz square wave with DC coupling on your oscilloscope?

author: Peter_O
author_rank: Frequent Contributor
timestamp: December 13, 2020, 05:14:13 pm
content: Quote from: radiolistener on December 13, 2020, 04:45:38 pmSure.Your shot above might show a misaligned probe compensation.

author: radiolistener
author_rank: Super Contributor
timestamp: December 13, 2020, 06:00:21 pm
content: Quote from: Peter_O on December 13, 2020, 05:14:13 pmNo, I got screenshot for well matched 50 Ohm connection with direct RG58 cable

author: Peter_O
author_rank: Frequent Contributor
timestamp: December 13, 2020, 06:11:26 pm
content: Just for my curiosity: What are you after when asking for a 100Hz square wave shot?

author: radiolistener
author_rank: Super Contributor
timestamp: December 14, 2020, 05:11:06 am
content: Quote from: Peter_O on December 13, 2020, 06:11:26 pmjust interesting how your oscilloscope response (at low frequency) is flat in comparison with my oscilloscope.Your oscilloscope has very flat response at low frequency

author: bdunham7
author_rank: Super Contributor
timestamp: December 14, 2020, 05:20:56 am
content: Quote from: radiolistener on December 14, 2020, 05:11:06 amSomething is funky with your setup....trynotusing a 50R termination to start with.

author: radiolistener
author_rank: Super Contributor
timestamp: December 14, 2020, 05:56:03 am
content: Quote from: bdunham7 on December 14, 2020, 05:20:56 amAll is okay with setup. The setup is just 1 meter RG58 coax cable with BNC connectors connected from 50 Ohm gen output to oscilloscope input. With 1 MOhm input mode the same issue.This is due to non flat frequency response of oscilloscope at low frequency.You can also see this issue on the ramp waveform above (SDS00096.png), just look at the bottom corner of the waveform

author: bdunham7
author_rank: Super Contributor
timestamp: December 14, 2020, 06:03:15 am
content: Quote from: radiolistener on December 14, 2020, 05:56:03 amSo what does a 1 Hz square wave look like?

author: radiolistener
author_rank: Super Contributor
timestamp: December 14, 2020, 06:27:06 am
content: Quote from: bdunham7 on December 14, 2020, 06:03:15 amHere is square wave for 1 Hz and 10 Hz.There is some change in amplitude between 20 Hz and 100 Hz. Just look for sine wave 20 Hz and 100 Hz.20 Hz = 1.22 Vpk-pk100 Hz = 1.16 Vpk-pkFor higher frequency oscilloscope also shows 1.16 Vpk-pk. So, there is a curve at about 20-100 Hz interval.

author: radiolistener
author_rank: Super Contributor
timestamp: December 14, 2020, 06:41:40 am
content: Full set for comparison1 Hz, 10 Hz, 100 Hz, 1 kHz, 10 kHz, 100 kHz, 1 MHz, 10 MHz square wave.All wave is 1.20 Vpk-pk.oscilloscope: Siglent SDS1102Xcable: 1 meter RG58cable loss:0.101 dB at 1 MHz0.070 dB at 10 MHz0.070 dB at 20 MHz0.081 dB at 30 MHz0.080 dB at 40 MHz0.103 dB at 50 MHz0.123 dB at 60 MHz0.142 dB at 70 MHz0.174 dB at 80 MHz

author: Peter_O
author_rank: Frequent Contributor
timestamp: December 14, 2020, 08:24:29 am
content: Have you tried another cable?Have you tried another FG?

author: radiolistener
author_rank: Super Contributor
timestamp: December 14, 2020, 09:48:27 am
content: Quote from: Peter_O on December 14, 2020, 08:24:29 amyes, I tried RG402, RG316, RG174, RG58, tried different length - 1 cm, 5 cm, 10 cm, 20 cm, 32 cm, 50 cm, 100 cm, 200 cm. Exactly the same behavior.Quote from: Peter_O on December 14, 2020, 08:24:29 amyes, exactly the same behavior with different generators.Even more, other people with the same oscilloscope have the same issue.Here is result 100 Hz square wave on another generator (hand made XR2206):

author: radiolistener
author_rank: Super Contributor
timestamp: December 14, 2020, 11:08:09 am
content: And another generator si5351.Connected directly into oscilloscope connector through SMA-BNC adapter.10 kHz, 100 kHz, 1 MHz, 10 MHz and 100 MHz square wave with rise time 1 ns.Since signal rise time is 1 ns, you can also see actual oscilloscope rise time: 2.6 ns. So, the actual bandwidth is 134 MHz.

author: radiolistener
author_rank: Super Contributor
timestamp: December 14, 2020, 11:40:21 am
content: And another generator ADF4351.Connected directly into oscilloscope through SMA-BNC adapter.50 MHz, 100 MHz, 150 MHz, 200 MHz, 250 MHz, 300 MHz, 350 MHz, 400 MHz, 450 MHz and 500 MHz square wave.Amplitude is 0 dBm (635 mVpk-pk).

author: Peter_O
author_rank: Frequent Contributor
timestamp: December 15, 2020, 08:50:53 am
content: What about Siglent's or dealer's support?

author: radiolistener
author_rank: Super Contributor
timestamp: December 15, 2020, 10:36:26 am
content: they know about that and sent me replacement main board. But I still didn't tried it. It is still sealed. Guarantee period is expired, so need to test a new board. But I'm scary that board replacement may break some calibration and I lose my oscilloscope

author: Peter_O
author_rank: Frequent Contributor
timestamp: December 15, 2020, 11:22:09 am
content: But as they agreed in this to be a failure of the board, it might be a good idea to take the risk. And nobody here showed up so far, who saw a mistake on your side.