SDG6022X QAM Mod. displayed on SSA3032X-R  - Page 1
Forum section: electronics / testgear

author: markus_jlrb
author_rank: Regular Contributor
timestamp: September 13, 2023, 07:38:46 am
content: Dears,I have the opportunity to play with the SSA3032X-R device.I'm using my Siglent SDG6022X AWG to play arround with QAM IQ Signals.In order to make some tests with the dmod utility of the SSA3kX-RI have used a QAM64 signal with center at 100MHz and 300ksps.The SDG6kX generates a fixed message length of 4096 patterns.But when setting the SSA to different message lengths (128, 256, 512, 1024, 2048, 4096)I see a significant increasing error rate (EVM%) with the increaseof the message length that I could not fully understand.perhaps someone can give me some explanation on this issue.I would expect the same error rate when the IQ signal is of a stablequality.So in this specific case my question is if I'm wrong and have to adaptmy QAM knowledge or did the SDG or SSA or both have some issuesin generating or/and demodulating the QAM signal.For better understanding I attached the SDG 64QAM Setting as well asthe screenshots for the 128 - 4096 of the SSA while demodulating.The stat values where reseted after message length change.Many thanks for your explanation in advance.Markus

author: tautech
author_rank: Super Contributor
timestamp: September 13, 2023, 09:45:11 am
content: Sync instruments together or to a common 10MHz reference.

author: markus_jlrb
author_rank: Regular Contributor
timestamp: September 13, 2023, 02:24:47 pm
content: Thanks tautech for your reply.According to my knowledge the receiver of theQAM signal (the SSA) should recover the clockproperly and sync on the accurate sample pointin the iq data stream when jitter could be neglected.That was what I had learned 30 years b4 at SIMENSin the digital lab for point to point communicationvia QAM in the field of radio link science and development.At that time I was a student doing my practical educationin this field.Meanwhile I'm not involved in this field anymore so doingthis for hobby purpose and perhaps I had forget someprinciples after that long time, so please correct me if I'mwrong.I will follow your hint and sync both devices to record thedifference.For this purpose I could use the clock of my R&S CMU200that is equipped with a high precision clock source.Markus

author: markus_jlrb
author_rank: Regular Contributor
timestamp: September 14, 2023, 07:14:47 am
content: Thanks tautech,to point me the proper device config.As already stated by you the error rate decrease significantwhen syncing the clock of both devices.I have attached only the spectra of the 4096 msg lengthQAM64 signal without and witch clock sync as well as someadditional spectra of the SA and RTSA mode.I enjoy the time playing around with this device.MarkusMarkus

author: nctnico
author_rank: Super Contributor
timestamp: September 14, 2023, 11:12:42 am
content: Quote from: markus_jlrb on September 13, 2023, 02:24:47 pmYou are right about that unless the SSA doesn't do clock tracking. But that would defeat the purpose as you can't sync to the clock of an LTE tower (for example) you might want to measure.

author: markus_jlrb
author_rank: Regular Contributor
timestamp: September 14, 2023, 05:31:35 pm
content: @nctniconice to read this - I was doubting my old knowledge.In the case you would like to receive as LTE sig from thetower, you need your own clock recovery which is not alwayseasy to achieve especially when you have propagationdistortions and overlapping due to multi path.This was the most difficult problem to be solved duringmy time in the lab decades ago.Many genius engineers were working on this problemto solve for QAM128 and QAM256 during my time atthe company and elsewhere. The had developed adaptiveequalizers to regenerate the clock and data stream.Was a very interesting time for me as a young student.Markus

author: nctnico
author_rank: Super Contributor
timestamp: September 14, 2023, 06:22:55 pm
content: Nowadays you can do such things in software on a PC with an SDR. Still not easy but you can receive & track an LTE signal for sure. I've done some high level programming in this area to track the clock synchronisation of LTE towers.

author: tautech
author_rank: Super Contributor
timestamp: September 14, 2023, 08:50:18 pm
content: Quote from: markus_jlrb on September 14, 2023, 07:14:47 amI cannot know how you did these tests therefore suggested you sync instruments however there maybe something else going on.Try referencing one and not the other.Maybe also remove the mains earth between them and rely on the signal cabling to bond them.But agree it shouldn't be this difficult but unfortunately I do not have an analyzer to do tests right now.Bump me for tests at the end of Sept.

author: gf
author_rank: Super Contributor
timestamp: September 15, 2023, 11:47:05 pm
content: Quote from: markus_jlrb on September 14, 2023, 05:31:35 pmThat's where OFDM (with many subcarriers and a low symbol rate per subcarrier) can help.I thought that LTE would use (a variant of) OFDM anyway, and not raw QAM

author: markus_jlrb
author_rank: Regular Contributor
timestamp: September 16, 2023, 09:40:54 am
content: Dear responders to my thread,we have not to mix my intention just testing the QAM64 Modulationgenerated by the SDG6022X on the SSA3032X-R as a playground Idid while testing the SSA which I get borrowed, with the mentionedproblem of measuring radio signals from a LTA tower mentionedby nctnico, which is more sophisticated as only connection two devices(SDG and SSA) via plain coax cable (clock synced or not).If the SSA3kX-R could be used for this kind of wireless LTE measurementis not clear to my due to lake of knowledge in this field especially in termsof LTE.I'm more keen of collection some knowledge in DVBC/DVBS transmissionand the usage of such RT SSA device for diag purpose.Markus