hi Tom thanks for pointing that out.
I'm running the sketches on a mega 2560
to find out if my cable was actually sending signals a first used an Analog Input output sketch from the library. this involved dimming a led, with a pot. first the standard setup with short jumper wires.it worked.
also the serial monitor gave me figures from 0-255,as expected.
then i used the same sketch, but this time with the long cable.Dimming did't work and no values on the serial monitor.so i got a new cable.this time a telephone cable.Dimming the pot worked.
The serial monitor however only showed values only from 0-55,which i can't explain.
But still a successful test as controlling the led was possible.
Next step was using this cable and inclining it in the Servo Knob setup.
I used the Servo knob sketch from the example list in The IDE.
However i took the advice on powering the servo externally.grounded everything correctly.and everything worked. the servo can be controlled from 0-to not quite 180 degrees.Hardly any jitter
The cable I'm using is only three meters long.Next step is getting a three phase cable with eight meters and also taking the 0,1 uF capacitor between analog input and ground arduino on board.
sketch and diagram will also be posted
so far so good,thanks