I see, so adding 4 more channels to a radio that has 7 channels already, may be too long of a PPM frame? Wish I had a scope.
Don't steal, the government hates competition.
Do you have an Arduino kicking around? There's free code & software online to use one as a simple scope. When I first started thinking about this project my oscilloscope was at work so this is what I used - It was absolutely fine for the PPM stuff
I believe there are some simple sound-card-scope instrucitons online too. Haven't tried that myself.