On Fri, 02 Mar 2007 15:06:40 GMT, "Teri Buck"
wrote:

I am using a multi-switch to change radios and antennas. One of those MFJ
1700Bs. I get different SWR readings depending upon where I place the
bridge in the tangle of wires that go into and out of the switch. If I
take the switch out of the equation I get very low SWR. With it in I get
2.5:1.

All of the coax has a common ground so the OCF windom also shares a common
ground with the coax going up to the beam and all the radios. All grounds
are starred at the back of the antenna tuner and run to earth.
I am wondering - does the common connection mean the coax shield to the beam
is becoming a part of the OCF windom antenna and vice-versa?

Would it therefore be adviseable to put current chokes on all the ins and
outs of the switch? Other comments?

k4ia
Buck


Based upon your description you can bet the farm you've got common
mode problems. Off center fed dipoles (that's what you have - its not
a windom) are notorious for that problem.

You'll need to install some good common mode chokes (high choking
impedance). For an OFCD you'll need two or more on the coax feed
line. I would start with one at the antenna feed point and another
where the coax enters the shack.

Danny, K6MHE