jcpearce wrote:

Thanks for the input.
Perhaps going with a linear power supply would be the way to go, I did
not as there are already three switching DC-DC power supplies on the
MB, the power efficiency is less than 50% for linear and I would have
to deal with the heat issues. I could just string a bunch of LM78xx and
LM79xx to get the required positive and negative voltages.

I've created a seperate smaller case for the PSU as creating a new
single case would have taken longer and I don't know about what level
of cooling issues I will have. I've noticed the PSU manufacturer (not
surprisingly) has reducd the MTBF when it is in hotter conditions. (but
hey perhaps I could use the heat to warm my cold toes in the Long Ez)
If the weather clears tomorrow I will go flying and measure how much of
a problem I have with it operating.

Thanks for the continuing input.
The LM79XX's will do you no good unless you have a source of negative
voltage to feed them. This generally will mean a dc to dc converter which
generally means switching regulators. Try putting your current powersupply
in a case and attach it directly to the MB's case and use feedthrough
capacitors in the common case bulkheads to feed the dc voltage in. Put
fedtrough caps and ferite beads on the dc in to the powersuppply case.
Cheep and will get you a good start to eliminating the noise.
John