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PTT wiring

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zsmith3rd(at)earthlink.ne
Guest

Posted: Sun May 06, 2007 9:35 am Post subject: PTT wiring

do not archive



Ed,



Since there is usually not any easy way to suspend the wire in a nearly-vertical stick other than the connections on the switch, let me offer this:  Use RG-58C/U coax.

This breed has stranded center conductor for flexibility, and the shield can be used as the strain relief.  Accomplish this by finishing the PPT switch end  such that the center conductor is a bit longer that the shield.  Solder the center to one side, then pull the shield into the switch enough to put slack in the center conductor.  Just a slight bend in the center conductor is sufficient.

The shield, back at the radio or intercom box, goes to ground/earth while the center serves as the PTT.



Being 'shielded' serves on particular purpose electrically, but the shield does serve mechanically.

Just be sure you don't use solid center conductor.



Regards,



Zed

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dredmoody(at)cox.net
Guest

Posted: Sun May 06, 2007 10:19 am Post subject: PTT wiring

The ptt switch current is described  by RAC as less than 50 milliamps (which is the rating of their  momentary switch). Since the responders indicate that this low current is not  likely to be a noise problem for the radio/intercom, the remaining issues are  supporting the wiring inside the stick, using non-toxic Tefzel wire, and  assuring flexibility of the wire due to stick movement. 

  

 RAC takes care of the support issue by having the  wire looped through the mounting plate of the switch twice near the solder  point. I feel that is adequate support for the wire so using the shield of  a coax wire for anchorage should not be needed in this application.

  

 The suggestion to use a wire that won't poison me  before I burn to a crisp in a fire sounds like a good one, so Tefzel it is.  Nobody likes a toxic corpse.

  

 Likewise the suggestion to avoid solid wire is well  taken; braided wire it is then. Twisting the pair may reduce what little RF  noise they produce so that will be done too.

  

 Someone mentioned somewhere in the archives I  believe, that there should be a gromment guarding the wire from chaffing at  the point at which it exits the bottom of the stick. I have a few  large O.D. grommets (about 1 inch or so) with very small center holes  (about1/8"). If I can wedge one of these into the bottom opening of each  stick with the wires threaded through them, that should do the job  nicely.

  

 Thanks to Paul and Zed for the help and  advice,

  

 Dred

  

 I think this deserves  archiving.

   [quote][b]

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kkinney

Joined: 11 Jan 2006
Posts: 42

Posted: Mon May 07, 2007 6:11 am Post subject: PTT wiring

I have an Xcom-760, which shows 22ga, twisted pair for the PTT's.  

You can make your own twisted pair by chucking the wires in a drill and spinning them.  Release them and let the wires relax.  (Credits to Bob Knuckolls and the AeroElectic Connection.)

For future reference - Here's a link to the AeroElectric FAQ -

www.aeroelectric.com/FAQ/AeroElectric-List/AeroElectric-List_FAQ.pdf



It's fairly large and at 310 pages, you wouldn't want to print it.  I've downloaded it and search it whenever I don't have my print copy of AeroElectric Connection at hand.



Of course, EVERYONE owns a copy of the AEC, don't they?  Seriously, it's an excellent resource.  After attending one of BK's classes and RTM, I feel minimally competent to wire my own machine.  

And for someone who knew nothing about aircraft electrical systems, that's saying a lot.



Good luck on your project,

Kevin Kinney

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dredmoody(at)cox.net
Guest

Posted: Mon May 07, 2007 9:07 am Post subject: PTT wiring

Thanks again to all. The right stick should do fine with a homemade twisted pair. The left one with its nine conductors will be more of a challenge.



Dred

Do Not Archive

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