[aprssig] Pulse Mod

Jack Cavanagh cjcav at earthlink.net
Mon Sep 25 21:48:23 CDT 2006

Andrew Rich wrote:
> Gudday
> I have been looking closely at how aircraft send their positions using 
> ADS-B on 1090 MHz.
> The data burst is around 112us and happens every 0.5 second.
> Just wondering why we as hams do not do such a thing ?
> Is it the bandwidth restrictions ?
1090 Mhz is the frequency used by IFF systems (now the politically correct secondary radar systems) 
for the response from an aircraft to an interrogation from the ground.  The basic IFF mode A (W.W.II 
era) the respose is a one microsecond pulse.  Other modes use pulse codes to report altitude, 
aircraft ID and, in the case of a military aircraft combat mode and encrypted response to an 
encrypted interrogation.  ADB-S is an evolution of the IFF system.

Pulse modulation can be used on UHF and higher amateur bands.  However, this will vary by 
administration and I have no idea what the Australian administration allows.  I don't even know what 
the the USA administration (FCC) allows, but I do know where to look it up.

   Sure, data transmission by pulse modulation is possible.  However, when the FCC in the USA 
changed the power limits from 1 kW average input power to 1.5 kW PEP output, pulse modulation at low 
duty cycle became unattractive.   Oh well, so much for my ham radar.


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