[aprssig] Solar Powered Digi's and Voice Alert.

Robert Bruninga bruninga at usna.edu
Wed Dec 5 12:15:15 EST 2007

>> When a local net is activated, the call 
>> goes out on Voice alert asking everyone 
>> to QSY to the local APRS packet channel.
> WHAT???  You're suggesting running a voice 
> Net on the APRS packet channel?  

No.  That "local APRS packet channel" is *not* the national APRS
channel.  But a separate local non-144.39 channel.

> Mixing modes like that is bound to be 
> deleterious for all users.

On the dedicated local APRS digital channel used for local area
net-support and operations for special events/emergencies, mixed
modes is more permissible, because there will be orders of
magnitude fewer users and the channel can be used as best needed
to support that operation.  Remember, APRS was originallly
designed as a PTT mode where voice is predominant and the APRS
data just tags along in 200ms at the end.

> I thought the idea of voice alert was for 
> infrequent calls and immediate QSY.  

Yes, that is what the original sentence is.  A one-time Voice
Alert call to tell all local 144.39 users that may be involved
in the situation to QSY to the local APRS *alternate* channel.

> Any more than that, or even that in a busy area, 
> [on 144.39 national channel] and you're asking 
> for trouble.

Agree completely.

> > 1) The local channel does not have the QRM from out of area,
so the 
> > channel load drops to only 5% of what it normally is.  This 
> improves 
> > APRS reliability by a factor of 20 or more, even low power 
> trackers can 
> > Be operating there without being clobbered.
>    At first look, that's patently ridiculous.  How can you 
> say that the 
> local packet channel will drop to 5% of it's normal 
> activity???  Where's 
> all the traffic going?  It'll still have all its normal APRS 
> activity, 
> PLUS the out-of-area QRM inserted by your wide-area x-band 
> voice repeater! 
> And I don't see a way to easily implement a carrier-sense and 
> holdoff on 
> the voice repeater, so it'll be the ultimate channel hog: a 
> highly-placed 
> high-powered transmit-only device!
>    You'd be better off turning your project around 180 
> degrees.  144.39 
> PL100 input, UHF output.  That way, the local APRS network(s)
> unaffected, and just those who need and choose to hear the
> voice alerts can have the capability.
> -- 
> Rick Green N8BJX
> "Those who would give up essential Liberty, to purchase a
> temporary Safety, deserve neither Liberty nor Safety."
>                                    -Benjamin Franklin

More information about the aprssig mailing list