VARA HF , TRI MODE and the SDR #SDR #VARA


Graham
 

VARA HF  , TRI MODE and the SDR

The   use of SDR and the  VARA HF modem is  limited to  , SDR  one side of the  connection  only 
ie Conventional <> SDR  , or  SDR <> Conventional 

Where as VARA FM and  VARA Sat , support SDR<>SDR 

As V modem deploys dynamic timing , adjusting for symmetrical & asymmetrical   
link  delays , this at  first sight, looked a little  'odd 
considering, the  FM and Sat versions are 100% compatible 

It transpires that  VARA HF latency cannot be  extended , due to the  
requirement to  be compatible with  TRI Mode  band  scanning limitation  of 4 seconds 
in which, the delay from only, one  SDR  may  be  accommodated ..this may not 
be  fully recognised  and  could  present  un-expected  issues  ..

Implications :- 

VHF 'FM'  1.2/9.6  Unaffected   
V-SAT   unaffected 

HF gateways  deploying  SDR may  fail to  connect  with  SDR  clients
conventional tx/rx may be  required  to  provided  conventional & sdr connections 

VARA-HF-Chat  SDR<>SDR may not  function  *

*NB-  VARA -SAT  will  function with  Chat  SDR<>SDR  
over HF link - 

Unless the  SDR  processing times  are   reduced  and/or  the  4 second  Tri-mode scan  
issue is addressed , the situation  remains precarious , with legacy issues influencing
HF gateway configuration .. extending the  V-HF latency [accommodation] is at odds  with 
the  Tri-Mode  scan  cycle  ... catch 22 

73-Graham
g0nbd

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