Hello and thank you for your detailed reply. As I said I just have RF modules that have no PPM decoders, PPM encoder is not problem because any RC transmitter has PPM output, I just connect it to TX module.
But on the receiver side is the problem I have RX module that outputs PPM signal and I have to decode it so the servos of the airplane can work. I have been searching a lot and finally found what I need: PPM decoder that has at least 8 channels and has programmable failsafe on at least 1 channel (that is made by user "mem")
On every modern rc system even cheap chinese receivers that cost around 10 USD the PPM decoding is done with atmel as far a I know.
So I thought this is the best http://dx.com/p/nano-v3-0-avr-atmega328-p-20au-module-board-usb-cable-for-arduino-118037
it has USB connection so I don't have to buy any programmers. Where I live buying only the atmega will cost as this whole board or more.
So yes I only need PPM decoder that has at least 8 channels and Failsafe. Without this I can't control the model.
If it is possible
to decode more than 8 channels it will be great, because with more channels you can control more things for example lights and other misc stuff.