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[aprssig] Too many digi's ?

Robert Bruninga bruninga at usna.edu
Sun Oct 22 15:52:20 UTC 2006


> ... Dual receive sounds like a better step but it 
> raises the complexity.  Sometimes you can't do this 
> at the mountain digi because of logistics. 

Dual receive is a great way to cut collisions almost in half.
It simply means putting two TNC's and TWO receivers at the digi
each connected to small 2 element beams or so.  Just something
to give about 10 dB or more difference in receiving on one side
of the mountain to the other side.  This way, each side can hear
two packets at the same time that otherwise would have collided,
but becauise of the different antenna patterns, the FM capture
efffect makes sure each one is heard OK.

Then they both feed tehe same transmttter but with their PTT's
crossconnected to the External Carrier Detect input of the TNC.
That way, they do not collide at the transmitter.  You could
even do this for three TNC's and 3 receeivers if the geography
of the high site digi has that kind of groupings.  This would
triple capacity.

De Wb4APRR, Bob

> Perhaps the thing to concentrate on after the new paradigm is 
> establishing power recommendations for stations?
> 
> 73 de Pat --- KA9SCF.
> 
> 
> On 10/20/06, Keith - VE7GDH <ve7gdh at rac.ca> wrote:
> 
> 	Bob WB4APR wrote... 
> 	
> 	> That is another way to do it, but the alt-input digi 
> takes only
> 	> the setting of the -600 offset at the digi and it's
done.
> 	
> 	But if this is a single transceiver listening on 
> 144.990 and transmitting 
> 	on 144.390, it would be transmitting blind without 
> listening on 144.390.
> 	It's a nice idea, but wouldn't it really take two TNCs 
> & two radios to do
> 	it properly... or at least one TNC & a transceiver on 
> 144.990 / 144.390
> 	plus a receiver on listening on 144.390 to at least 
> listen to see if the
> 	frequency was clear? Of course, in busy areas, it may 
> never be clear.
> 	Perhaps it would be no worse than mobiles transmitting 
> from an RF 
> 	black hole and not knowing that someone the next valley
over was
> 	already beaconing.
> 	
> 	73 es cul - Keith VE7GDH
> 	--
> 	"I may be lost, but I know exactly where I am!"
> 	
> 	
> 	
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> 	
> 
> 
> 





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