Nathan Young wrote:

I checked this afternoon. It is mounted on the engine side of the
firewall. The model is a Hisonic RFI 70. It's probably as old as the
plane, so I wonder if it has any capacitance left, or is merely along
for the ride.

-Nathan

If that Hisonic box is about 2" X 3" X 4", and has two terminals
(instead of one), it is actually a low pass filter containing series
rf chokes wound on ferrite as well as shunt capacitors. If it has just
one terminal, then it is likely just a shunt capacitor, where the
case is the other side...

In either case, the case has to be well grounded for it to have any
effect. The capacitor(s) in these things are high quality, and usually
do not dry out.

Mike M
Skylane '1MM
Pacer '00Z