I just attempted to make use of the PPM capabilities of the APM2, and I'm running into some odd issues.
I'm using the ChainLink Dare UHF Tx/Rx (with Turnigy 9x and er9x firmware) system which has a PPM port on the receiver. I hooked that up to the Input channel 1 on the APM and jumpered channels 2 and 3. As far as I understand, that is the way to enable PPM input on the APM2 board (despite what the wiki says).
I connected the APM2 to Mission Planner to see if all the channels were working, and they do appear to respond to tx inputs. However, all of the channels are jumping around quite a bit. Have a look at the plot above.
Any ideas as to what might be causing this?