[TowerTalk] coax cable charge dissipating through reed relay contacts

[Al Williams]

I am in the process of rebuilding the cabling for my M2 2800 rotator.  In order to reduce or eliminate errant pulses from coupling to the reed relay return lines I have been planning to use some old RG58 coax.  The run will be about 200 feet.

However, I believe it was Tom Rauch who cautioned about using coax in this application because of the charged coax lines discharging through the reed relay contacts and possibly damaging or welding them together.  

I think that the M2 design applies 12v  to one reed relay contact through a ~2k resistor and thus to the 200' coax line.  And the other side of the reed relay contact is connected to the circuit ground.  Thus the 200' coax line, of approximately 30pf x 200 feet, is a capacitor of about 6000pf.

The resistance path of 2 (?) x 200' is probably insignificant to reduce the outrush current.  However would there be enough inductance?  What about the effect that the capacitance is distributed?  Is using coax going to be ok or should I change?

k7puc