PPM Advantages

Our servos use 3 connection wires: plus, minus and pulse.The pulse connection uses exactly the same 1-2ms servopulse as generated by the transmitter, meaning the complete transmission chain is transparent. The representation of the information is not altered.Therefore transmitter and receiver can get by without processor,the only possibility in the past. That way they can be easily built, small and cheap. There should be no problems using different makes of receivers with transmitters from other manufacturers. Every 22.S-ms-Frame contains the complete servo position. Transmisson is fast enough to operate even the quickest of servo's. With PPM ,the end of the transmission range is shown by the servo's starting to move erratically. When the pilot starts to notice this( control movements are no longer transferred correctly), he could probably still get his model back home safely. Momentary signal losses get ironed out by the model's inertia.

Disadvantages

Due to its simplicity, PPM transmission cannot detect errors, the receiver does not see the difference between valid and invalid servo pulses. It starts counting after every starting pulse and , for example, steers the 7^th pulse toward the 7^th servo exit. If there is a short glitch (0.5 ms), halving the first servopulse, two undersize, faulty pulses appear, going to exits 1 and 2. The second pulse , that was unaltered, goes to exit 3 etc. If the glitch is long enough (>30 ms), it could be seen as a starting pulse and pulse counting in the receiver starts at an arbitrary channel. This can only get corrected in the next frame. When the range boundaries are reached, pulses get slightly longer or shorter because of noise. Servos start to move eratically. The same thing happens when antenna orientation is not optimal, when the projection of the receiver antenna is nearly down to a single point, the signal breaks down and the servo's get false pulses. These short glitches go unnoticed most of the time because they are smoothed out by the servo's inertia( "slowness").

Translation to the picture:

Störung - distortion
ohne/mit - without/with
Störung während des 1.Pulses - distortion during 1st pulse
Servoausgang - servo output