ORIGINAL: Bob Laine
Mounting the batteries one on top of the other, has no bearing on the noise generated by the ignition. the ignition battery is isolated from ignition noise at the switch. Batteries make, nor do they transmit ignition noise. That's why it's important to keep the ignition switch as close to the ignition module as possible, and the receiver switch mounted as far from the ignition switch as possible. You can use the batteries anywhere you desire to achieve the proper balance.
DON'T THINK SO
These ignitions do NOT have a nice smooth 500ma (or whatever) draw. They take a big spike of power the instant after the spark happens. Some of the spikes are in the multi amp
range. This spike impresses a noise on the ignition battery that is equal to RPM. A battery is yards of metal and will act as an antenna and "send" the noise to the RX battery.
We spent hundreds of hours developing the "rules" on the installation needed for a CH ignition. Yes these rules were developed with AM and PPM radios. Yes PCM may or may not be better, but remember that PPM and PCM BOTH use the same FM carrier to send the signal and the first several stages of the RX are the SAME. When you lose frames with PPM the rx will send out random noise to the servos and cause them to move erratic. When you lose frames with PCM the servo is frozen. IN NEATHER CASE DO YOU HAVE CONTROL OF YOUR PLANE.
An installation shouldn't be the minmum needed to make a safe flight but the very best you can do. Give your plane a chance to live through a situtation where something has happened to the RF link