[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: ranging experiment: Measure different snr's. Re: AO-40 Link S/...



In a message dated 01-09-25 01:48:32 EDT, nn0v@home.com writes:

> Ranging: Transmit a 1.5 khz tone of 9 cycles.
>  Record with a mixer the uplink audio and the downlink recieve.
>  Measure the delay with sound editor.
[snip]
>  Hm seems my resolution is quite large.. +-94 miles I will try this with
>  an FM repeater at known distance and see how I can do.

This is really interesting.   What sampling rate are you using 
on the sound card? Back of the napkin calculations suggestion 
that at 44.1 kHz sampling rate you should get "about"  

resolution = (speed of light in miles per second ) / (samples per second)

or about ( 186282 / 44100 ) = about 4.22 miles per sample at best.

This is only an estimate, since it ignores the delay through
the transponder (was this value ever published?) and the
delay through your receiver.  In addition, the speed of radio waves
is not a constant going up to the satellite (vacuum v.s. air)
and coming back down.

As I recall, James Miller's ranging experiment used a 
similar (but different) method to do ranging, where he 
transmits a "special" bit stream instead of just carrier 
cycles. 

This might be a fun project for a soundcard and some
Pentium DSP.  Anyone want to help me?

Douglas KA2UPW
dquagliana@aol.com
----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home