I am using an LND712 with an 8.5 meters long RG6 coaxial cable. The anode resistor is exact near to GM tube at the other end of cable. I have used compensation capacitor as well.
The system works and gives no issues but as soon as I touch the cable with my hands, spurious counts appear. Why such noise gets introduced just by touching. Using a long cable has been a problem with my project. Any ideas in why the problem on how to solve it ??? Is it due to cable capacitance ? Or any other reasons ?
Good you included that drawing to make it clear what you meant.
It is no wonder you get spurious counts when you touch the caox shield, since you connected the very high impedance cathode to it.
If possible, you should connect the shield to the HV supply, and the cable core to the cathode!
However, I am a bit concerned about carrying a voltage that high over a coax cable designed for SAT receivers…