[aprssig] Re: AO51 Digipeater Trial Test

Robert Bruninga bruninga at usna.edu
Thu Dec 22 22:33:40 CST 2005

>I have tried to send APRS spots over AO-51 using my 
>TM-D700 and ... the ...exercise has not been very satisfying.  
>...on 435.300 I hear voices faintly.  When I switch to 
>435.150 I hear nothing.  When I listen on my base 
>satellite rig / antennas... the S-meter registers S5 or better 
>and I can distinctly hear the 9600 baud packet burst. 

Yes, but remember, that your UPLINK from your APRS mobile
has an over 22 dB better link than the very weak downlink. 
That is, your chance of hitting it is 150* times better than 
hearing it which is exactly why the mission of this mode
for mobiles with mobile antennas is to be heard, and for a
few sat-gate ground stations then to hear those digipeats
and to feed them through the global APRS internet linked
system to all of the various APRS data engines.  That is,
an AMSAT amateur radio position reporting and email input 
system for mobiles anywhere on the planet.

Remember that from the front panel of a D700 or D7 you
can send an email to anyone anywhere... if you can be
heard.   The ECHO digipeater brings that capability everywhere
on earth at least a few times a day.

Of course, portable stations with ARROW or other gain antennas
can use the system two-way station-to-station such as 
for messaging out of an area with no other services.

But this takes both sides of the coin.  We need sufficient
sat-gates feeding the internet to make sure that a packet
sent from an HT actually gets into the system.

* Why is the upolink 22 dB (150 times) stronger?  SImple.
>From an omni-to-omni antenna, the link is 9dB stronger
on VHF than UHF..  Plus the mobile is running 50W 
instead of 2.5 W

It will take us a while to get the satg-ate system in place
and reliable, but it will be worth it!

de Wb4APR, Bob

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