[TowerTalk] coax cable charge dissipating through reed relay contacts

[Matt Patterson]

 Al,

I'm using RG58 on a 250' run to my Orion 2800 and have had no problems.  I
couldn't tell you about all the technical aspects of the coax when used this
way though as I'm sure others on the list can.  All I have is practical
knowledge of something that I have in use at my QTH.  If you're afraid of
using coax I have a friend who ran two lengths of 3 conductor romex to his
Orion and that also works well.

73 Matt
W5LL 

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Al Williams
Sent: Sunday, July 17, 2005 8:36 PM
To: towertalk at contesting.com
Subject: [TowerTalk] coax cable charge dissipating through reed relay
contacts

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


 
_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk