Hi Buly,

You will get more effective filtering by putting a choke in series
with the lead to the offending unit.  Put the capacitor on the end
away from the noise generator.  I looked at RS and only found one
choke of 100uH, but it didn't give a current rating (p/n 273-102)
They also have a snap together toroid core that you could use to make
a choke.  Wrap as much wire, of the appropriate gauge to carry the
current, as you can (p/n 273-104).  They also had ferrite choke core
(p/n 273-105) that you can just clip around the wire.   It will work
best if the noise is high frequency.  You should be able to reduce the
size of the capacitor when used in conjunction with the choke.

Bob W.


On Fri, 24 Feb 2006 19:40:00 -0500
Bulent Aliev <atlasyts@bellsouth.net> wrote:

This morning on the way to the hangar I bought some more ceramic disk
capacitors 0.01mF as suggested. Tried them on the fan. No change. The
fan is Spal brushles I think? It has separate return line to the
engine case.
While waiting for Jim to come with the oscilloscope, I connected
(temporary) the large 20A Radio Shack noise filter to filter the
incomming power to the avionics bus. BIG improvement! I would say 80%
reduction in fan, fuel pumps etc. noise.
Jim arrived with the o.scope and we connected it to the fan. Wow! You
can see the noise. Started trying different disc capacitors I had and
they did not make any difference. Jim asked me to buy few different
ones at RShack and left to take care of business, but left me the
o.scope. After trying few capacitors, 475mF did the trick.
Now the high pressure FI pumps. They were making one hell of a noise
filling the whole screen on the scope.
The avionics filter was taking care of most of it, bit I can still
hear them. Went twice more to RShack for bigger and bigger
capacitors. Finally the 2000mF made difference on the screen, but not
enough. On the way home I stopped again in RShack and got the biggest
one they had 5000mF and hope in the morning to see a flat line on the
screen :).
Next is the alternator, but had no time to run the engine today.
Thanks to everybody for your suggestions.

QUESTION FOR TRACY: At all times with everything else turned off
except master, I hear quiet noise in the headset that's like a clock
ticking. If I disconnect the antenna from the radio it stops. I was
wandering if there is something in the EC that maybe doing this?
Buly





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