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Intercom wires

 
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cfi(at)conwaycorp.net
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PostPosted: Wed Jan 09, 2008 5:57 am    Post subject: Intercom wires Reply with quote

Hello all. I recently purchased a SoftComm 4-place panel mounted intercom that comes with a pre-wired harness. I am very surprised to see that the wires from the audio panel and to the headsets are not shielded. Would it be prudent to replace these wires with shielded ones or will it be ok using them as-is? If you're using this product with the harness as provided, please send me a PIREP.

Thanks!
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
Michael



[quote][b]


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nuckolls.bob(at)cox.net
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PostPosted: Wed Jan 09, 2008 6:51 am    Post subject: Intercom wires Reply with quote

At 07:54 AM 1/9/2008 -0600, you wrote:

Quote:
Hello all. I recently purchased a SoftComm 4-place panel mounted intercom
that comes with a pre-wired harness. I am very surprised to see that the
wires from the audio panel and to the headsets are not shielded. Would it
be prudent to replace these wires with shielded ones or will it be ok
using them as-is? If you're using this product with the harness as
provided, please send me a PIREP.


Virtually all audio system wires in aircraft
receive 99.99% of their immunity for noise
propagation by (1) twisting outbound and inbound
signal return lines and (2) elimination of ground
loops. Shielding is a prophylactic against
ELECTROSTATICALLY coupled noises of which there
are exceedingly few sources and next to none that
live behind the instrument panel.

While not a 100% sure deal, suppliers of such
products will have conducted due diligence in
crafting the design of their offering . . . while
working to reduce $time$-out-the-door price of
their product. Leaving off the shields is low
risk if (1) and (2) are dutifully satisfied
and it reduces $time$ required to produce the
product.

At the moment, I have no basis for telling you
that the supplier did a bad thing. Go ahead and
install it as-is.

Bob . . .


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jdubner(at)yahoo.com
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PostPosted: Wed Jan 09, 2008 7:03 am    Post subject: Intercom wires Reply with quote

Michael,

I'm using the two-place version of this intercom and factory harness in
my Long-EZ with no problems. 660 hours/5 years/12V system/IR
alternator/strobes/Lycoming O-235 with 1 magneto and 1 LSE EI.

I can't see shielded wire improving the performance of the earphone
wiring (it's low-impedance and high-level) although I can _imagine_ it
_possibly_ helping for the microphone. But in practice, all is fine.

If I had an aluminum airplane, I'd be sure to mount the jacks with
insulated shoulder washers to avoid picking up a ground common to other
(noisy) circuits.

Incidentally, Softcomm is one of the "good guys" -- they provided me
with a schematic of their intercom when I needed to fix it (blown LM386
output IC -- an easy fix).

Best,
Joe
Lewiston, ID
Email: http://mail2600.com/#Contact
On 01/09/2008 05:54 Michael Hinchcliff wrote:
Quote:
Hello all. I recently purchased a SoftComm 4-place panel mounted intercom that comes with a pre-wired harness. I am very surprised to see that the wires from the audio panel and to the headsets are not shielded. Would it be prudent to replace these wires with shielded ones or will it be ok using them as-is? If you're using this product with the harness as provided, please send me a PIREP.



Thanks!



Michael


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trigo(at)mail.telepac.pt
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PostPosted: Wed Jan 09, 2008 10:00 am    Post subject: Intercom wires Reply with quote

By the way, Bob

On a broader view of noise protection, let me ask a general (perhaps too
much general) question:

In TC or OBAM aircraft, which of the wires of all used in present electrical
installations must be (or should be) noise protected, and from those which
shall be twisted and which shall be made from shielded wire?
Apart from the ground-loop and careful grounding procedures...

Carlos
[quote] --


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nuckolls.bob(at)cox.net
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PostPosted: Fri Jan 11, 2008 7:44 am    Post subject: Intercom wires Reply with quote

At 04:54 PM 1/9/2008 +0000, you wrote:

Quote:

<trigo(at)mail.telepac.pt>

By the way, Bob

On a broader view of noise protection, let me ask a general (perhaps too
much general) question:

In TC or OBAM aircraft, which of the wires of all used in present electrical
installations must be (or should be) noise protected, and from those which
shall be twisted and which shall be made from shielded wire?
Apart from the ground-loop and careful grounding procedures...

Carlos


Only those called out as shielded in the manufacturer's installation
instructions. These will be generally limited to strobe head wires,
p-leads, spark plug wires, and the occasional avionics system signal
wire.

The notion here is that nobody knows more than the manufacturer about
the probability for the device becoming either an antagonist or a victim.

Having said that, it's not uncommon for a manufacturer to call out
prophylactic noise mitigation processes that make no sense. I.e.,
twisting of power wires going into the back of a transceiver. The
shielding of a power wire coming out of an electronic ignition
power supply. Shielding the b-lead and field-lead on an alternator
(I was at Cessna when we crafted that canard!).

The only risk here is that what ever process is called for is at
worst the byproduct of someone "whistling-in-the-dark" about noises
for which there is no demonstrable experiment. On the upside, the
well crafted system that truly benefits from adding filters or shields
acquires those recommendations for good reasons.

Bob . . .


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