[Elecraft] open wire feeders

[Ron D'Eau Claire]

Open wire (or 'parallel conductor') feed lines connected to a reasonably
balanced load do NOT radiate (or receive noise, etc.) 

The currents, hence the electric fields, around each wire are opposite and
equal at all points, even though the line may have a high SWR. Those equal
and opposite fields cancel, meaning no radiation from the line nor can an
external RF field induce a current in the line.

Note that a "perfect" open wire line has two attributes. Both conductors are
in the same physical space -  a physical impossibility - and the load is
perfectly balanced - physically more possible but not common. 

However, spacing the wires a small distance apart (in terms of wavelength)
and a reasonable amount of balance in the load still results in a
transmission line that is as free from radiation or unwanted pickup as many
coaxial lines. 

Note that coaxial line itself suffers from the fact that the outside of the
shield is a conductor at RF completely separate from the inside surface of
the shield, since RF travels only on the surface of a conductor, not
"through" it. So, if you have 50 feet of coaxial line running from your
antenna to the rig, you also have a separate 50 foot random wire antenna
leading into the shack. That's why special care must be taken to control or
suppress currents on the outside of the shield to avoid "RF in the Shack"
issues with coax.  

Ron AC7AC

-----Original Message-----


Those of you using open wire feed lines. How do you keep RF out of the  
shack? 73 George/W2BPI K2/100