MOTM

3 people have noted that using longer (over 20") power cords makes the '485 
twitchy.

This is due to the very high impedance FET buffer picking up AM radio signals 
(really!)

Use only 20" power cords, and mount the module *away* from any VCOs or Power 
supplies.

I haven't tested this, but you *may* see improvement if you *replace* the 2 
ferrite beads  (L1/L2)
with 33 ohm 1/4W resistors AND increase C1 and C2 to 100uf (Mouser 
647-UVZ1V101MED at 35 cents each).

Old Crow noted that on the BP version of this filter such a newtork was needed. 
Might be worth a try (this I'm not doing as
an official change).

Paul S.