Saturday, October 18, 2008
Friday, October 17, 2008
Ordered some 60mw XBee modules and a USB XBee interface from
http://robosavvy.com for the Mashroc telemetry project.
I'm going to be building a small PIC based board for the rocket end of
the system and running some tests to check range and
see if there are any doppler related problems.
I did a few quick and dirty doppler calculations which came up with :-
Source f = 2400000000 Hz
Source Velocity vs = 118 m/s (Guessed)
Medium Velocity v = 3000000 m/s (Approximately Light)
Observed fo = 2399905603.71292 Hz
Observed delta do = -94396.2870793343 Hz
I found from a zigbee spec online (must find a better source) the
frequency tolerance is 40ppm which I took to mean 2400*40 = 96 KHz. So
we're just inside the tolerance.
Bear in mind this is worst case doppler with freq source moving directly
away from the observer.