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Com issues - resolved

 
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berkut13(at)berkut13.com
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PostPosted: Fri Feb 16, 2007 8:54 pm    Post subject: Com issues - resolved Reply with quote

Well gang...it's fixed.

I added 150ohm resistors to all input audio leads into the panel.
Everything is living together quite nicely now. I guess something in the
combination was not playing well with the new radio.

However, there was one wild card that might also have something to do with
it. While I was removing, moving, installing, and re-installing the pins in
the 134's connector, one of the ground leads (mic I think) broke off a pin.
I was forced to strip and crimp a new molex pin on there and re-secure.
This was done in the same operation as the resistors. After all that, the
audio was loud and clear with all radios mixed in, regardless of the
combination. I'm not convinced this was the issue, since the radio did work
correctly by itself.

So...was it the resistors?...was it a bad ground?...was it a gremlin?
Personally, I don't care anymore...it's fixed!

Thanks for all the help, everyone. Nothing like beating your head against
the wall in a cold hangar.

James Redmon
Berkut #013 N97TX
http://www.berkut13.com


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nuckollsr(at)cox.net
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PostPosted: Sat Feb 17, 2007 6:27 am    Post subject: Com issues - resolved Reply with quote

At 10:47 PM 2/16/2007 -0600, you wrote:

Quote:


Well gang...it's fixed.

I added 150ohm resistors to all input audio leads into the panel.
Everything is living together quite nicely now. I guess something in the
combination was not playing well with the new radio.

However, there was one wild card that might also have something to do with
it. While I was removing, moving, installing, and re-installing the pins
in the 134's connector, one of the ground leads (mic I think) broke off a
pin. I was forced to strip and crimp a new molex pin on there and
re-secure. This was done in the same operation as the resistors. After
all that, the audio was loud and clear with all radios mixed in,
regardless of the combination. I'm not convinced this was the issue,
since the radio did work correctly by itself.

So...was it the resistors?...was it a bad ground?...was it a gremlin?
Personally, I don't care anymore...it's fixed!

I suspect that your victim radio was being loaded down by
and exceptionally LOW output impedance of the other radio.
With its low output impedance, it was able to deliver useful
audio output energy into a system that was "loaded" not only
by the system that drove you headphones but by the other
radio. This is the phenomenon explained in the audio systems
chapter I cited earlier.

Adding the resistors artificially raised the output impedance
of all sources. This degrades the transfer of energy to the
headphones . . .but no so much that increasing radio volume
can't overcome it. At the same time, it breaks the ability
of a radio having exceptionally low output impedance from
exercising the loading effect you were experiencing.

Bob . . .

----------------------------------------
( IF one aspires to be "world class", )
( what ever you do must be exercised )
( EVERY day . . . )
( R. L. Nuckolls III )
----------------------------------------


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berkut13(at)berkut13.com
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PostPosted: Sat Feb 17, 2007 7:04 am    Post subject: Com issues - resolved Reply with quote

Yep, I read that chapter and found it very enlightening. When I was wiring
up the airplane, I skipped that section since I out-sourced the panel wiring
harness to a local avionics shop. I guess another lesson here is to read the
WHOLE book when you're building airplanes...'cuz if you are maintaining
airplanes too, you are going to need ALL the info sometime in the future.
Wink

Bob, thanks again for the education.

-James
---


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