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nuckolls.bob(at)cox.net
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 Posted: Wed Sep 03, 2008 12:30 pm Post subject: Noise Filter for Strobe power and regulator? |
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At 06:12 AM 9/3/2008 -0600, you wrote:
| Quote: |
Bob,
Regarding my interest in a noise filter for my strobe:
>**
> Now does noise from the strobe manifest itself
> in your system?
>
> **
I was told it was audible via the intercom and the previous owner had
glued (literally) a massive aluminum electrolytic to the top of the case
(the size of a tall drinking glass) "which helped" (as I remember being
told). I'm redoing the wiring from scratch and it's possible that
elimination of a previously existing big radio/intercom power feed loop
will have taken care of the problem but it seems prudent to put some
filtering in to replace the overly large cap.
My goal is to put in something "reasonable" and, with luck, not have
anything to chase down in this area when I power everything back up again
after the rewiring.
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This is a LongEz? Where is the strobe supply mounted
and how is it grounded? Do you have a single point
ground system? Where are the microphone and headset
jacks grounded?
Bob . . .
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steve(at)tomasara.com
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| Posted: Thu Sep 04, 2008 4:55 am Post subject: Noise Filter for Strobe power and regulator? |
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| Quote: |
** >Bob,
>Regarding my interest in a noise filter for my strobe:
>>**
>> Now does noise from the strobe manifest itself
>> in your system?
>>
>> **
>I was told it was audible via the intercom and the previous owner had
>glued (literally) a massive aluminum electrolytic to the top of the case
>(the size of a tall drinking glass) "which helped" (as I remember being
>told). I'm redoing the wiring from scratch and it's possible that
>elimination of a previously existing big radio/intercom power feed loop
>will have taken care of the problem but it seems prudent to put some
>filtering in to replace the overly large cap.
>
>My goal is to put in something "reasonable" and, with luck, not have
>anything to chase down in this area when I power everything back up again
>after the rewiring.
This is a LongEz? Where is the strobe supply mounted
and how is it grounded? Do you have a single point
ground system? Where are the microphone and headset
jacks grounded?
**
It's a LongEZ, I'm redoing the wiring (all of it..., In fact there is no
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wire left in the airframe right now, but I made a full set of
"as-builts" before I ripped it all out) as I didn't like some things I
found. The first issue that I think could have been a big contributor
for strobe noise is that the power and ground for the radio and intercom
stack (which was one breaker for all, but will be separate fuses) ran
different directions from the radio with the ground running forward to
the battery while the power ran backward on the left side, crossed over
to the right side through the pilot headrest and then forward to the
switch panel in the right strake before continuing forward to the
battery. This left a huge inductive loop for noise pickup. This will
be fixed. The strobe power was mounted under the wing spar in the "hell
hole" and was grounded both directly to the firewall (via case mounting)
and through a power cable that ran up to the switch panel which there
had a separate ground back to the firewall. This put the the strobe in
the middle of one of the ground loops (all of which will be
eliminated). The radio, intercom and instruments, and this is worth
something..., were at least on a separate non-looped ground direct to
the battery. At the jacks, the mic and headphone jacks were only
grounded to each other and to a ground wire and the shields on a closely
paired pair of shielded cables back to the avionics harness. There was
technically a ground loop in the two shields but not an egregious one as
there was no area within the loop (but it will be fixed none-the-less).
From your questions I'm inferring that noise problems with a Whelen
Strobe supply is not a given. And I'm now expecting you might suggest
that since I'm rewiring and eliminating an obvious noise propagation
path (that from the nice open power supply ground-loop to the nice open
radio power path loop...) and possible other less-obvious ones (and
hopefully avoiding any of my own design) perhaps I should wait on the
noise filter until I determine if I still have a problem.
(In student mode...) How'd I do?
Steve Stearns
Boulder/Longmont, Colorado
CSA,EAA,IAC,AOPA,PE,ARRL,BARC (but ignorant none-the-less)
Restoring (since 1/07): N45FC O235 Longeze Cothern/Friling CF1 (~1000 Hrs)
Flying (since 9/86): N43732 A65 Taylorcraft BC12D
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