Re: digital modes on 2m 70cm


Graham
 

Bruce 

Interesting  point on the  military aircraft , popular rumer had/has  it , that one of the  local  police , out on traffic speed  duty , close to a  scottish air base , out of curiosity , pointed his  hand held 'speed gun' at one of the  aircraft coming  into  land , which lit up the  counter measures suite , end of career .. 

Its more to  re-radiation , most of the  aircraft to  day are  composite hulls ,  [one of the reasons for the  11 meter  ww2 radar , was aircraft wing was round 35 feet , so it gave a  good  return  signal]  so the  signals are not as  good as  in the past , polarisation ,  probably Horizontal , I would  expect the  return  signal to  be modified  , dopper plays a part as well , so the  decoder needs  to have a  wide  acceptance 
bandwidth , I think the  doppler shift is up to  x2  if the  target is  advancing ,  first shift  tx> a/c  then a/c >> rx  , at 600 mph , that's  round  +150 Hz on 2 meter's  ?

Ive  found this  write up  by two  spanish  stations  using a  plotting/ prediction software package to  give the  expected  angles / range , google translate makes a  good  job  of converting  to  english , just noticed it was  back in  2014  , when the  decoder was re-worked  during the  eme  testing

http://hamlincs.blogspot.com/2014/04/aircraftscatter-144mhz-con-opera.html?fbclid=IwAR3KXz9kxfm9-ePVvANjWkI4iOAfG0JtbV76Jps3TC4TXv3gQZUbTHYgJ5Y

This was a  scatter  spot , from a French  10 watt  70 cm  beacon, using a  halo round  Ae to  south of france   to paris 704 Kmt , confirmed by 
the  keeper 

19:56 432418 F5ZAS de F1RJ Op05 -19 dB F:2% in JN18AT 1390,6 Hz

>> Foxsix Htj Yes, Aircraft Scatter, big airplane above Clermont Ferrand (matching with AirScout software).

73-Graham
g0nbd

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