> Also the output to FMS is the raw data before it is being transmitted.
> That is why on some older tx w/o trainer ports, you could still build a
> FMS cable by patching directly to the circuit board.

FMS supports two distinct serial protocols:

1) "Serial IRQ interface", which works only in Win 9X (unless you use PPjoy or similar drivers).
FMS itself senses the channel pulse duration in PPM frame and converts it to the channel positions.

2) "Serial PIC interface", which is natively supported in all Windows versions including 2000 and XP.
FMS reads channel position numbers from the serial port and it's a responsibility of a microchip inside the interface to decipher the PPM frame and convert duration of each pulse into the corresponding stick position. FMS has less work to do, which is immediately visible in the increased frame rate (assuming the video card is fast enough and the CPU load theremins the FPS).


In any case, the PPM signal is extracted from the pransmitter before it gets modulated (AM or FM) with a radio frequency.
I myself converted Hitec Focus 3 by adding a trainer connector with the signal wire going to one of the legs of the encoder chip.

Getting back to Zhen Hua transmitters: they use the standard PPM frame format (with the same zero and min/max durations as everyone in the industry) and the only time I've seen them doing something different, except for messing with protocols, is introduction of non-disableable CCPM mix (which is only done in their CCPM transmitters).