Some IMPRESSIVE experience in this group.

I have not heard "tempest" in years.

But again, in my experience, if you've got a metal box already. It's
most likely the connector and harness.

Carry those grounds (on the harness shields) through!



AINut wrote:
Look up info on "Tempest" PC's. Lots of good methods for RFI
suppression.


jcpearce wrote:
Thanks for the suggestions, no I have not posted what I did
anywhere
but I think I will as it took me a little while to learn
rudimentary
assembly, come up with a variant of linux running off flash memory,
write the code to process the serial output and display etc..

I did not use a hobby aluminum case, I custom built one with no
gaps
(motherboard has a temperature sensor so I could check this for
possible overheating) and this was grounded. Without hooking up the
data aquisition card and just powering up the EPIA M in the
seperate
aluminum case with no connections of any kind to the airplane I get
the
interference in the radio. There are no connections coming out of
the
aluminum box except for power and this line has caps on it for
filtering.

So it is coming solely from the motherboard, some chip on the board
is
oscillating in the 107~130 Mhz range, given this occurs against one
home computer running at 2Ghz, another at 2.4 Ghz and the EPIA and
500
Mhz I would guess it is some supporting chip, but even if I knew I
am
not sure that would do me much good. Perhaps changing the aluminum
case
to a different size/shape would catch the offending frequency but I
am
in the dark here and would be shooting in the dark.

There only seems two generic routes,
A) find a small computer which does not emit these frequencies (but
I
do not know what is emmiting them so I would not know which
computer
choice would alleviate this)
B) Some vastly better shielding approach for the motherboard.

Ideas?

Thanks



Bob wrote:

The "noise" could be coming through the connector and could be

emitting

from the wires.

Try using a connector with a metal housing and backshell and wires

with

shields, terminate the shields to the connector backshell/housing

which

will ground to the chassis.

The other end of the wires, try to terminate their shields where
they
connect to.

Aircraft environment is not the same as home environment.
Different
applications different techniques.

jcpearce wrote:

As a pet/learning project I made a data aquisition unit using an

8051

microprocessor and an EPIA M motherboard running a variant of
Linux

to

process and display the information. It all works but the EMI from

the

EPIA M causes way too much noise to the aircraft radios. I have

tried

shielding the whole device in an aluminum case with very little
improvement.

Any ideas on how to smother the EMI or some other small
motherboard
which may not have as much an issue (as a test I took my portable
aviation radio and within 6' of any my home computers the same

occurs

which gives me little hope)

Thanks