VARA -SAT- Dynamic net facility #VARA


VARA  -SAT-  Dynamic net facility 

This puts  portable operation  , from  low power non gps locked systems on the  table 

Latest version , contains an interrogator , which,  produces a response  from the  wanted  station , 
indicating the  level of  frequency   'off net'  [ similar to  IFF  or Secondary radar ] 

This allows  a connecting  station to  'find'  the  wanted  gateway , and to  then  commence  transmission
[ solving the  age old problem with  duplex sat work of  netting ]

The  vara-sat version , now has  undergone  considerable  testing  and  modification over the  geo-sat link, and now  provides extended  latency  , with  enhanced  AFC 

PA1SDB , Conducted  low power test  and reports  data  transfer with   70 mW to  120 cm dish  ,  the  Modem  reached  level  3  , the  maximum  un-registered speed  173 baud  , problems  experienced , where  trying to  reduce the  power, to a  lower level ! , 

Follow the  progress  , being  reported  on the  Amsat-DL  web-site

Roberto IS0GRB Testing the  system with  his  RMS gateway , posts  :-

This evening Jose EA5HVK has released the version 3.0.5 of the VARA SAT modem.


This version, at our request, integrates the Calibration function, very useful via satellite and for those without GPS.

In the Calibration menu the client transmits a signal to the server, normally controlled by GPS, or to another client controlled or not by GPS, which reply with its signal and the shift detected by the client who launched the test.


It is therefore possible to know your own AFC value detected by the correspondent and center the VFO, so as to reset the AFC to 0 (zero) without the aid of a WebSDR and therefore of internet connection.


Roberto IS0GRB


dg0opk   Lists  equipment  used  

[SDR console ,  has  beacon  AFC-Lock , specially designed  for the  Sat
used the  band edge  CW beacon to  lock  qrg]

Peak Data Rate: 3500bps


setup using:

TCXO LNB with software drift correction on QO-100 BEACON (SDR Console), ADALM PLUTO (TCXO MOD) in FULLDUPLEXMODE, SDR Console V3.0.11 ,Virtual Audio to Vara Modem, RX/TX Switch ... VOX Controlled by SDR Console




Reports , sending  70 Kb  in 4 min 18  sec , via :-

IS0GRB Winlink Server on QO-100 (Dial 10489635.0 USB)

Bernd  posts 

''This morning I made  a speed measurement with VARA SAT with winlink express via OSCAR-100.

I sent a file with app. 70 kbytes size from Zirndorf, Germany to IS0GRB island Sardinia ( Italy ).

I have a FTDX3000, a signalink sound card and the DL2BZ transverter driven by Leo Bodnars great GPSDO.

The file was sent in a time of 4min18s.

The sat  version of VARA has  extended  time  delay to  accommodate the  path length , enhanced  AFC  and  'ping' netting facility to  enable  fast  netting to  be achieved ,

Features that  may also  be  useful  , for  less precise  HF use, perhaps VFO controlled set's   , or  systems with  long  tx/rx change over times ..noting the  modem  , unlicensed  , remains  in the  lower speed  MFSK modes and as such , may be  used with  a variety of non linear systems -  eg  qrp  using  class  D power amps etc [ if your installation  is  licenced ,  entering a  random key  will  effectively de-register , being restored when the  correct key is  entered ]