XPS Technical Support Forum

Hi,

Need more channels.
Radiomaster TX16S in XJT can output 16 channels.
J1 Module handles this, that's great.
Radiomaster TX16S in PPM can output 16 channels.
Recall that the J1 Module will only handle 8 Channels. 
To refresh my memory is this correct?
I can't find a reference to it, time to update notes.

Regards,

The maximum number of channels that you can have in PPM mode, per the official specification is 8 channels.

However, you can have more PPM channels if you increased the frame rate.  This is what Graupner and Multiplex do with their radio systems.  The PPM specification calls for 2.2ms x Number of channels +  at least 4.9ms.  With a typical 8 channel radio that gives you a frame time of 22.5ms, which is a frame rate of 44.4 times per second.  32 channels would require more than 75ms, which is ~13 frames per second, making it too slow really for controlling a RC model - especially if dropped frames occur.  XPS transmitter modules support up to 32 channels in PPM mode.

Long frame times means a lot of latency, which iis why protocols like Xtreme, XBUS, SBUS, XJT, etc. exist.  The Xtreme protocol supports up to 256 channels, and a frame rate as low as 3ms with 4 channels.