PPM and PCM are still both FM but the PCM filters better. I use them both with gas engines and haven't had any RF problems. It's more about learning how to set up A gas plane then the radio you are using. With 2.4 you can get very sloppy and not have any problems, with FM you have to set up your plane correctly. Do yourself A favor and read up on both gas plane set up and the Futaba 9-C series of radios. The Futaba site is very good and there are several forums you can learn about gas plane set up right here on RCU. Your LHS probably has books on the subject. It isn't all the hard and I have run into this stuff on other web sites. At present I'm setting up A 30% Extra with A G-62 with A mag, not an electronic ignition and I'm betting there will be no RF to worry about or have to trace looking for A problem. I'm using my 9-C and A PCM RX. Do some research!!!