Today's Message Index:
----------------------
1. 07:09 AM - Re: 1 Amp Fuses (Chuck Jensen)
2. 01:16 PM - Re: Nav/com 'acoustic feedback' (Miskelly, Francis G)
3. 04:36 PM - Re: PTC (Robert L. Nuckolls, III)
4. 07:39 PM - Design Questions (MTBehnke)
5. 09:57 PM - D-Sub Pin Extraction ()
Message 1
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The Chinese are building the old style fuse boxes with the screw in
fuses. They were having trouble making the screw in fuses that fit in
the fuse box. Every resourceful, they decided to supply each fuse
socket with a penny on a string. This is considered an upgrade since
the screw in fuse would only carry 5 amps but the penny...much more.
Distributed by Mattel. :-)
Chuck
Message 2
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Subject: | Nav/com 'acoustic feedback' |
Feedback for the list
This problem was due to the poor intercom on a Bendix/King 155 picking
up radio interference and was solved by adding an external intercom
(I've included the correspondence as it contains useful info)
- Frank
1. The radio is a Bendix/King KX155
2. It is approximately 1 year old. Don't know the model # but could find
out
3. It definately has an internal intercom but i've no links to describe
it
4. I didn't check whether the sound varied depending on where your
head/headset is sitting, or by
bending the wires around on the headset, or the wires to the jack but it
occurred with 3 separate headsets and on both pilot and co-pilot
outputs. Pretty sure its not a headset problem as same headsets work
fine in other planes
5. The noise gets worse with higher engine RPM but is very obvious even
at 1000 RPM. The character doesn't change - just its loudness
Many thanks
Frank
<mprather@spro.net>
Interesting.. I wasn't aware that any KX155 has intercom. Okay. I see
the manual says it has 500ohm aux inputs, but don't see any reference to
intercom. We're talking about a Bendix/King KX-155, right? Do you have
a
link to a file which describes the feature?
Does the sound vary depending on where your head/headset is sitting, or
by
bending the wires around on the headset, or the wires to the jack?
Is the frequency of the whine/feedback dependent on the engine RPM? Or
is
it just a steady tone?
I agree with item 3 (assuming an intercom).
Regards,
Matt-
> Matt
> 1. When i cover the mic with my hand (muff off) the character of the
> feedback alters significantly but is not overall reduced. If i move
the
> boom away from my mouth and around to the back of my head then the
> feedback reduces but doesn't disappear. Its worse (louder) the closer
the
> boom to my mouth. These symptoms occur on both left and right hand
> headsets
> 2. My KX155 has an internal intercom. I haven't tried to disconnect
it.
> 3. Plugging in the mic jack should activate the intercom and the
transmit
> on the radio (when PTT pressed)
> 4. Remember the problem only occurs when the engine is running.
> 5. Does anyone know how to adjust the mic gain (intercom volume
control)
> on the KX155? Couldn't find this info in the installation manual.
> Kind regards
> Frank
>
>
> <mprather@spro.net>
>
> Does it help if you cover the mic with your hand (both sides - pull
the
> muff off)?
>
> I suspect that the input stage of your intercom is being overdriven by
the
> acoustic noise of the engine.
>
>
> Regards,
>
> Matt-
>
>> Thanks for your comments Ernest.
>> I've double-checked all the grounds i could find. Even took the whole
>> harness out (which was new) and had it double-checked. Nothing found.
>> If its the intercom in the radio why does it not cause the same
problem
>> when the engine is off?
>> It only causes the problem when the engine is running
>> Kind regards
>> Frank
>>
>> ________________________________
>>
>> From: owner-aeroelectric-list-server@matronics.com on behalf of
Ernest
>> Christley
>> Sent: Mon 13/08/2007 15:04
>> To: aeroelectric-list@matronics.com
>> Subject: Re: AeroElectric-List: Nav/com 'acoustic feedback'
>>
>>
>>
>> <echristley@nc.rr.com>
>>
>> Miskelly, Francis G wrote:
>>> The KX155 nav/com in my Glastar has 2 problems which may be related.
>>>
>>> 1. Inserting the headphone jack i have near perfect reception.
>>> However, when i insert the microphone jack there is a loud whine
>>> suggestive of 'acoustic feedback'. Moving the boom away from my
mouth
>>> reduces the whine. With a different headset it appears as lots of
>>> static noise which again changes with position of the boom. I've
>>> changed the aerial, power supply and checked all the earths. It
occurs
>>> with either mag and when the generator is disconnected. It only
>>> happens when the engine is running. The radio's been bench tested
and
>>> passed as good.
>>>
>>> 2. Radio reception is good with just the headphone jack inserted.
>>> However, insert the microphone jack and reception becomes very poor
or
>>> disappears completely. I suspect the 'acoustic feedback' is raising
>>> the automatic squelch which is cutting off the radio station
>>>
>>> Can anyone suggest an explanation and a solution!
>>> Many thanks
>>> Frank
>> Since there is a problem with multiple headset, I would check the
jack
>> first. The symptoms seem to imply some feedback from the mic to the
>> audio. Look for a short or a broken ground. Beyond that, it would
seem
>> circuitry withing the intercom is fritzed, and it gets much more
>> complicated.
Message 3
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At 09:24 AM 9/13/2007 -0400, you wrote:
>all correspondence to the list should not use a acronym the first time a
>item is used.. What is a PTC???
Positive Temperature Coefficient. The discussion was
about the trade-offs for incorporating Polyswitches
or their direct cousins . . .
http://www.circuitprotection.com/polyswitch.asp
. . .into the power distribution of light aircraft.
Bob . . .
----------------------------------------
( "Physics is like sex: sure, it may )
( give some practical results, but )
( that's not why we do it." )
( )
( Richard P. Feynman )
----------------------------------------
Message 4
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Subject: | Design Questions |
I have a few questions as I'm trying to work through my electrical design. I've
looked through the Aeroelectric book and other sources, but can't seem to find
answers to the following:
1. Is there some design guidelines for minimum fuse sizes to avoid nuisance trips?
I've seen a couple of people mention keeping current below 80% of the fuse
size. I also saw one recommendation on keeping below 50% for radios based
on transmitting current draw.
2. I have the Creativair strobe power supply. I noticed that the strobe kit came
with 22 ga. shielded wire to go from the power supply to the strobes. The
installation instructions give Joules per flash, but nothing about voltage, current,
etc. I don't have any way to validate whether 22 ga. is okay, especially
as it's round trip distances. Should I just assume it's fine?
3. This may be overly nit-picky, but do you generally use 12 or 14 volts when
calculating loads? For example, I have the Duckworks 100W landing light. Using
12V gives 8.3A versus 7.2A using 14V. On top of that, a 5% drop of 12V is
0.6V compared to 0.7V for 14V. I'm not sure if this would result in any different
wire or fuse sizes.
Thanks,
--------
Mike Behnke
RV-9A Fuselage
Andover, MN
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=134314#134314
Message 5
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Subject: | D-Sub Pin Extraction |
I need to reverse the direction of my autopilot roll servo. This involves swapping
two wires that go into the servo D-Sub connector.
I have extractred pins from D-Sub connectors before, but I always had a free end
of the wire attached to the pin to thread through the groove in the extraction
tool.
This may be a stupid question, but how do I get the extraction tool around the
wire when I don't have a free end to the wire? This would be easy if I had a
free end to thread into the extraction tool groove, but a free end isn't available
unless I cut the wire!?
I sure don't want to cut the two wires, swap and then solder working in the belly
of my fuselage!
Am I missing something here?
HELP!
Paul Siegel
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