Ed G wrote in
.81:



The feedline is doing more than transporting energy to the dipole
centre, it almost certainly carries a significant common mode current
and in that case is just as much a part of the radiating system as the
dipole itself.

So, isn't the coax and control line to the SG237 carrying current mode
RF current, ie contibuting to radiation.

Inch by inch, the detail unfolds.


Yeah, inch by inch. I hate to fill up the post with too many
details as some people grab something insignifcant and go off on a
tangent.... however, the devil may be in the details.....

Yes, the people who modelled your antenna based on half the information
got an incorrect answer.


You're right on the current in the shield. We have a choke balun,
currently located 85' down the coax toward the transmitter. I have it
scheduled, when it stops raining, to move it up to the input of the
SG-
237 coupler unit. The Choke balun is homemade, 6" diamter, about 11
turns of RG-8X coax. Does that sound sufficient? I didn't make it or
provide it. There is no control line for the SGC coupler unit. It
only
requires 12VDC @ 300ma and we are providing that by using a couple MFJ
DC adapter units to feed the 12VDC up the coax.

You need to visualise that you what you have looks like a dipole with a
wire from one side of the centre following the path of the feedlines to
the choke and from the choke on to wherever.

The choke balun introduces a common mode impedance in that equivalent
wire, but it does not necessarily eliminate common mode current, rather
it modifies the amplitude and distribution of the common mode current.

Owen