[aprssig] Any audio recordings of 144.390 MHz ?

Robert Bruninga bruninga at usna.edu
Sat Oct 24 12:29:25 EDT 2009

> More precise measurement would take radio 
> RSSI signal, and account fraction of time 
> when it is over some defined treshold.  
> That would know not only of successfully 
> decoded packets, but also of failures
> due to two transmitters colliding at too 
> even signal power levels.

Yes!  Exactly,  Without RSSI, counting packet decodes is a
completely meaningless statistic as far as channel loading is
concerned.  Decodes only show success.  There is no way for
decodes to show all the failures.  And without comparing the
two, then there is no conclusions to be drawn as to network

Lets say 10 decodes a minute is measured.  This could either be
a near perfect channel with only 10 users at a 1 minute rate
getting 100% success... Or it could also equally be a totally
saturated channel with 100 users and only 10% of them have any
success.  A bad channel indeed.

That is why the ALOHA ALGORITHM is encouraged to be installed in
EVERY client SYSTEM.  This is a measurement we came up with in
APRS that can measure performace against the number of users and
expected number of packets.  The output is a circular RANGE
based entirely on what is heard on the local channel and is
independent of geography and density.  In Wyoming, it may be an
ALOHA range circle of 150 miles covering 70,000 square miles or
in Los Angeles it is a 10 mile circle covering only 300 square
miles.  But both APRS channels should give equal performance if
EVERYONE keeps their HOPS within their circle.

This is why all digipeaters in the LA area only digipeat ONE
HOP.  And in Wyoming, 2 HOPS works perfectly well out 150 miles
in all directions.

See www.aprs.org/aloha.html

Unfortunately, I do not think that the APRS-IS web pages can do
any meaningful ALOHA calculations, because the calculation must
be done on what a single receiver hears at a single location.
And since the APRS-IS throws away dupes, this makes remote
monitoring impossible.

IDEA!!!  Since the OUTPUT of an ALOHA caclullation at any one
site is a single NUMBER, we could ask ALL IGATES to make
continuous ALOHA calculations and INCLUDE their ALOHA RANGE in
their IGATE beacon.  This way, we COULD capture this information
for local, regional and national analysis!!!

Is anyone actively writing Igate code that wants to add this?


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