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SPA-400 wiring

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peter(at)mather.com
Guest

Posted: Sun Dec 16, 2007 2:59 am Post subject: SPA-400 wiring

Hi all



I'm installing a Sigtronics SPA-400 intercom and need help on a couple of 

questions.



First the intercomunit only has one ground connection rather than a separate 

power ground and an avionics ground. The radio has both. My plan is to 

create an avionics ground plane using a DSUB adjacent to the intercom, wire 

this to the power ground and then terminate the intercom's only ground and 

the radio avionics ground on this - does this make sense? What should I use 

as the shield on the wires to the radio - a separate connections to the 

avionics ground plane  left unterminated at the radio?



Secondly, based on the Sigtronics wiring diagram, the headphone output from 

the SPA-400 ties directly to the headphone output from the radio and all of 

the headphone sockets hang off this conection. Every other intercom/audio 

panel I've seen has the radio headphone output as an input and then has one 

or more separate outputs for the phone sockets. How does this work ifor the 

SPA-400? Is the SPA-400 making some assumptions about the electrical 

characteristics of  headphone output of the radio? It seems odd to be tying 

two outputs together but since there are so many SPA-400's around I assume 

its OK?



Any comments gratefully appreciated



Best Regards



Peter

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rv-9a-online(at)telus.net
Guest

Posted: Sun Dec 16, 2007 5:25 am Post subject: SPA-400 wiring

Hi Peter, the SPA-400 works fine as long as you follow their appnotes.  Most

comm radios will require a resistor (500 ohms or so) in series with the

output in order to function properly.  The Sigtronics intercoms use a

passive bus technique which has the advantage of working even with an

electrical failure in the intercom circuit.  As with most intercoms, wiring

all of those shielded wires is a major pain.



You can check out the AMX-1A from Vx Aviation here: http://vx-aviation.com/

It solves all of the grounding and matching required to connect a number of

different audio sources, and makes shield connections simple.  It' sold by

Aircraft Extras http://www.aircraftextras.com



Thanks,

Vern Little

RV-9A



 



--

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