Jim,
I agree!
I've been doing some balance measurements on a 100ft doublet I have fed
with ladderline. Because of its local environment it's a pretty
unbalanced antenna system.
I measured ladderline leg current balance using a couple of clip-on
meters; I also ran the ladderline through a single ferrite core wound
with pick-off turns to overcome the phase imbalance "uncertainty
problem". I tried the following arrangements:
Palstar BT1500 balanced tuner
Ten Tec tuner equipped with internal Ruthroff 4:1 Voltage Balun
Ten Tec tuner equipped with home-made external balun configured as 1:1
Guanella
Ten Tec tuner equipped with home-made external balun configured as a 4:1
Ruthroff.
The Ten Tec tuner plus external 1:1 Guanella produced noticeably better
current balance than any of the other arrangements - particularly at the
lower frequencies. The 4:1 Voltage baluns were especially bad.
I was unimpressed with the Palstar BT1500; the 1:1 balun it uses at its
input has pretty low CM impedance on the lower bands.
73,
Steve G3TXQ
On 14/11/2010 18:30, Jim Brown wrote:
> The primary concern with balance in an antenna system, INCLUDING THE
> LINE, is minimizing common mode current on the line. We care about this
> because we do not want the line to radiate to our neighbor's living room
> or receive noise from his computers, and because we do not want that
> common mode current in our shack. Indded, the primary function of a GOOD
> choke at the feedpoint (or down the line below a matching section) is
> to disconnect the feedline from the antenna from a common mode point of
> view.
>
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