Mmmmm.. First I'd like to thank Lintond for his very nice advises... Octd, you are saying that you use a Fortec ultra receiver. Well, if we are to blame the voltage drop then the F connector on back of your receiver should output two switchable DC voltages, 13V and 18V to change polarization V/H on LNB.
Question
oes your motor turn when you have the output for 18V DC using your 100ft cable? You can change the voltage from your
remote control unit... If not then you either have a very bad cable and/or connectors, or your motor is faulty. You should fix this problem otherwise you might damage your receiver. Don't forget that you are limited to 500mA to use for external devices such as motors, LNBs. If I were you I would use a Ampere meter to measure the current that is drawn from receiver when the motor tries to move. If you see 0 or very low amp drawn, then you have a bad contact somewhere in the path. If you see values > than 500mA stop!!!! You might have a leak or short circuit somewhere in the path. Disconnect the cable on motor side and test it again. If Amp goes down to zero then you motor is to blame. For
SG2100 for example the DC current values are 50mA stanby, 200mA for 13V and max of 350mA for 18V. Well, you can always use a dedicated positioner for your motor to off-load your receiver... Hope it helps,