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SDG6022X QAM Mod. displayed on SSA3032X-R

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markus_jlrb:
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-R
I 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 increase
of 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 stable
quality.

So in this specific case my question is if I'm wrong and have to adapt
my QAM knowledge or did the SDG or SSA or both have some issues
in generating or/and demodulating the QAM signal.

For better understanding I attached the SDG 64QAM Setting as well as
the 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

tautech:
Sync instruments together or to a common 10MHz reference.

markus_jlrb:
Thanks tautech for your reply.

According to my knowledge the receiver of the
QAM signal (the SSA) should recover the clock
properly and sync on the accurate sample point
in the iq data stream when jitter could be neglected.
That was what I had learned 30 years b4 at SIMENS
in the digital lab for  point to point communication
via QAM in the field of radio link science and development.
At that time I was a student doing my practical education
in this field.
Meanwhile I'm not involved in this field anymore so doing
this for hobby purpose and perhaps I had forget some
principles after that long time, so please correct me if I'm
wrong.
I will follow your hint and sync both devices to record the
difference.
For this purpose I could use the clock of my R&S CMU200
that is equipped with a high precision clock source.

Markus

 

 
 

markus_jlrb:
Thanks tautech,

to point me the proper device config.
As already stated by you the error rate decrease significant
when syncing the clock of both devices.

I have attached only the spectra of the 4096 msg length
QAM64 signal without and witch clock sync as well as  some
additional spectra of the SA and RTSA mode.

I enjoy the time playing around with this device.

Markus

Markus

nctnico:

--- Quote from: markus_jlrb on September 13, 2023, 02:24:47 pm ---Thanks tautech for your reply.

According to my knowledge the receiver of the
QAM signal (the SSA) should recover the clock
properly and sync on the accurate sample point
in the iq data stream when jitter could be neglected.

--- End quote ---
You 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.

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