Re: Understanding APSK and QAM Rohde and Schwartz video #VARA


Kristoff Bonne
 

Hi,


I'm a bit puzzled about this.

After watching the video, I I understand that QAM and APSK are two different systems, each with their advantages and disadvantages, and either with the specific usecase.

So I do not understand why combining QAM and APSK is then a good idea. You mix systems, therefor creating something that has the disadvantages of both.



What is the technical argument for these mil-comm systems to use a combination of QAM and APSK constelation?



Kristoff (on1arf)

On 06.08.21 19:01, ALE wrote:

Hi Graham,

QAM is fun, working to develop Military data modem and ALE serial tone modem QAM waveforms.

In my attached photo the QAM waveform in the constellation display is an MS110B offering, going into MS110C/D Appendix D and 4G ALE get even more complicated, I have not made it to 256-QAM yet, the Appendix waveforms and 3G ALE are in my near future however.

The SCS P4 serial tone modem stops at 32-QAM in less than a 3kHz channel, but the Military waveforms hit a the much  higher QAM  count and throughput in a 3kHz channel and then can increase the bandwidth and shift the PSK carrier up to incrementally increase the throughput.

My friend Dario maintains an excellent easy to understand technical blog on pretty much all the waveforms to be found on HF if one is interested in those subject matters at:

http://i56578-swl.blogspot.com/

<http://i56578-swl.blogspot.com/>/s/ Steve, N2CKH

At 02:21 PM 7/3/2021, you wrote:
R&S  , Useful series of  videos covering  aspects of radio
This video  is applicable to the  VARA modem  coding ,
makes  sense of the  displays  -

73-Graham
g0nbd


This video provides an introduction to the basic concepts of amplitude and phase shift keying (APSK) and quadrature amplitude modulation (QAM).
You-tube link :-

Understanding APSK and QAM <https://www.youtube.com/watch?v=1xGncBvWv6U>

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