Hacking receiver for PPM - signal inverted??

[weg22]

Hi all,

I opened up my Futaba receiver in search of the PPM signal. However, when reading it with an oscilloscope as shown on the following web page:

http://www.nobugs.org/engineer/uav/futaba-rx.html

I see the 9 pulses which correspond to my 8-channel receiver, but when moving one of the sticks on the transmitter the low portion of the pulse extends/contracts and not the high portion. It seems like an inverted PPM? Does anyone know what's going on? Is my interpretation of PPM (I thought it should show the high portion of the pulse extending/contracting) incorrect?

Thanks in advance,
-weg

[Mr.RC-CAM]

The demodulated and conditioned PPM's logic polarity, inside the Rx, can be whatever the responsible engineer needed to satisfy the input requirements to his decoder. This is NOT a FFM RF shift issue, but is a data slicer circuit thing that is determined by the overall design. If the observed signal is inverted from what you need, then just flip it over in your external circuit or accommodate it in your software.

[weg22]

What exactly do I need to "flip it over"? Some sort of resistor-transistor circuit?

Thanks in advance,
-weg

[Mr.RC-CAM]

Any inverter configuration you wish to use. Could be as basic as a NPN operated as a saturated switch. The options are endless. There may even be a compatible signal already on your Rx board.