Re: VARA vs. Pactor-III Speed Comparison Plots


Hello Graham:

It certainly was a time consuming process. It's interesting to note that short-term changes in propagation had less of an effect on modem speed than I expected. Speeds usually varied by 20 percent or less in the relativity short period of time it took to extract an average from multiple test runs.  

Jose did mention the changes he made to the protocol and I suspect it would have had a slight impact on the results. To your other question: no, I didn't measure variation in power consumption.

I'm not aware of any test data that includes Pactor-4 and VARA, but I suspect that would be something those in emergency communications would be interested in.   

Obviously, the proper way to compare HF modems would be under the controlled environment of an HF path simulator, but I think on-air testing can reveal certain throughput characteristics that may not show up on an artificial path. I think it all depends on how complex the real path is and what the path model limitations are.

Tony -K2MO 


 6/15/2018 10:37 AM, Graham wrote:

Hi Tony , More than 60 hour’s that was quite a feat !


There are some interesting points linked to the development of the  vara modem


The initial version, did deploy a change of protocol for the  lower speed  ranges , but,  with development , the  data  rates / s/n  of the  ofdm  modem ,  exceeded the  conventional  mfsk  rate/s/n.


Actually better  than 2fsk conventional rtty  , hence the  modem remains ‘single protocol’ ofdm  with  ‘low on air rate’ at all speeds  , with advantages of  noise rejection, selective fade , multiple path  over narrow b/w mfsk


Q:  When amtor  changes to  mfsk,  do you  note a higher level  of  power consumed ,ie , the supply current to the  Tx  increases , if so ,  what  change ?


Pactor  4


Q: Is it possible to run tests of the  vara  modem  against the  Pactor 4  modem, can anyone perform such a test ?


There  is a  interesting  ‘clash of  concept’ , with the  use of  high speed  serial  carriers , and the  low on air rate  multiple  carriers  of the  vara  ofdm  modem , to date , this  remains to be  explored …




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