I did a set of noise experiments using my Zaon MRX and my Icon A6.

The setup for the Zaon was (1) Flight Mode = On, (2) Brt down until
just disappears, (3) Antenna pointed vertically, (4) Power – internal,
external, external w/ 0.01uF ceramic and 0.1uF metal film caps in
parallel across power leads at tip going into Zaon (I couldn’t fit my
1” long by 1/2" diameter non-split ferrite into the test rig).

The setup for the Icom was (1) Frequencies 123.300, 123.075, 122.800,
(2) Internal batteries, (3) Antenna pointed vertically (4) unit on
opposite site of power input to Zaon and external battery.

The testing procedure was (1) Place antennas 3 inches apart, (2)
Reduce squelch from highest value until sound appears, note number,
increase squelch, reduce squelch, note number, repeat until lowest
consistent squelch number is obtained.

Test 1 – Zaon on internal batteries, Test 2 – Zaon on external
battery, no caps, and Test 3 – Zaon on external battery, caps used.

Results:
Test 1 Test 2 Test 3
Internal External Ext w/ caps
123.300 5 18 14
123.075 5 24 21
123.800 5 24 16

It’s clear that the Zaon radiates noise when running on an external
battery. It’s also clear that the 0.01uF ceramic and 0.1uF metal film
caps in parallel across the Zaon power leads reduce the noise the Zaon
is radiating, but they are nowhere near as effective as running the
Zaon on internal batteries.

Any electrical engineers out there who'd like to make some suggestions
for further tests to help me try and get the Zaon noise down?

-John