send command to  VNA

four parameters string each finshech  by  "enter" $oD 


MODE $0D   DDS_FTW $0D    SAMPLES $0D     DDS_STEP $0D   

---------------------------

MODE
"0"   VNA
"1"   Transmission

---------------------------

DDS_FTW  Frequency Tuning Word

DDS_FTW = F_start * 2^32 / DDS_CLCK

---------------------------

SAMLES  - how many measurment mus be done

---------------------------

DDS_STEP  Freq  steo  to next sample 

DDS_STEP = F_start * 2^32 / DDS_CLCK


//////  

answer from VNA -      just  raw data  with no any flow control  and stering chars..!!!
and not finished with any CR LF


just   if  You ask  for  "zero" sampler  you not receive nothing...

if  You   ash  for   "two" samppe  you  reveive  two "complete" of ADC values

AAAABBBBCCCCDDDD    

where    
AAAABBBB   is firs answer  from   two  ADC 0-1024  from first step
CCCCDDDD   is answer  form  second samples..



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EXAMPLE


0$0D23000$0D2$0D230$0D

vna measurment   two step   

..........................


1$0D23000$0D2$0D230$0D

transmission  measurment   two step