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europa(at)pstewart.f2s.co
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 Posted: Fri Jul 14, 2006 10:04 am Post subject: wiring PTT switches |
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Our set up is Microair 760 and XCOM intercom. should I wire stick top
PTT switches with single screened cable or a twisted pair. The wiring
diagram for the radio has the latter but their wiring harness (which
we are not using ) has the former. Also should I connect the PTT
switch wires in at the mic jack end or back at the XCOM box.
So many things in this plane that I know so little about !!
Regards
Paul Stewart
G-GIDY - -no longer sanding !!!!!!!!!!!
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europa flugzeug fabrik
Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA
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| Posted: Fri Jul 14, 2006 5:41 pm Post subject: Re: wiring PTT switches |
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| europa(at)pstewart.f2s.co wrote: | Our set up is Microair 760 and XCOM intercom. should I wire stick top
PTT switches with single screened cable or a twisted pair. The wiring
diagram for the radio has the latter but their wiring harness (which
we are not using ) has the former. Also should I connect the PTT
switch wires in at the mic jack end or back at the XCOM box.
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The PTT line normally shouldn't require shielding or twisted pair, and the manual on MicroAir's web site doesn't show that.
You would want a handheld mic to work if plugged into the mic jack, so both the control stick PTT and mic jack PTT lug get wired to the back of the XCOM box, however convenient to do so.
Fred F.
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europa(at)pstewart.f2s.co
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| Posted: Sat Jul 15, 2006 9:52 am Post subject: wiring PTT switches |
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Fred and John
Thanks for the help.My confusion has come I now realise because I
have an old installation manual which does ask for a twisted pair of
wires at 2 turns per inch to the PTT switches. I will follow your
advice and look forward to the sound of silence.
Regards
Paul
G-GIDY
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europa flugzeug fabrik
Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA
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| Posted: Sat Jul 15, 2006 11:09 pm Post subject: Re: wiring PTT switches |
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| europa(at)pstewart.f2s.co wrote: | Fred and John
Thanks for the help.My confusion has come I now realise because I
have an old installation manual which does ask for a twisted pair of
wires at 2 turns per inch to the PTT switches. I will follow your
advice and look forward to the sound of silence.
Regards
Paul
G-GIDY |
Paul, I hope I didn't steer you wrong, and you may have an iteration of the XCOM which requires shielding/twisted on PTT. It's possible you have a model of the box which is susceptible to external "noise." In older days, we switched between receive and xmit with a mechanical relay where this low impedance of flipping device didn't require any special wiring to prevent external noise from triggering xmit when we didn't intend to xmit. Modern comm boxes switch functions in semiconductor ways which are trivial now to prevent such problems, though they can be "hair-trigger" if not designed right, but the biggest nut to crack was isolating input/output (many volts vs. microvolts) from the single antenna which we use for receive/transmit (a simple, isolating, wonderous "PIN diode" for the technically curious).
Anyway, you mentioned your harness has shielded wire for PTT, so I would use that for as far she physically goes, not necessarily a ground in the shield. When we deisre to xmit, all we're really doing is pulling a "plus voltage" to ground, though a typically low resistance, hence noise immune. Nuthin' to worry about 'til you might run into an anomalous problem in servce. This function is trivial, and all you need is a ground return for your panel jack and/or PTT switch
Somewhat related here, but on my electronics bench right now is an eBay purchase of a Narco COM 120/20 for low price -- nominal 20W xmit on 14V. A rare device on the used market if alleged working and she does; and I purchased it for my other plane as a slide-in replacement for a working box. Why exactly I don't know, but that's eBay. Not that appropriate for a typical Europa, but holy mother of pearl!! She draws spec .5 Amps in receive, but key xmit and stuff sure happens. Measured 10A current draw, and thence better than 20-watt RF carrier output. The point is, you simply ground the PTT line from the back of the box, and xmit indeed happens if all normal.
Fred F.
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