On 6/24/16 4:36 AM, Paul Christensen wrote:
Although difficult to manage, one could place ammeters or shunted
pilot lamps at equal distances from the feed-point on the dipole
itself, and observe current. Some of the first experiments using
this method were developed during the 1920s and covered in QST. In
the early literature, transposition blocks spaced at regular
intervals along the line were used with the intent to force the line
into balance.
also the recommendation to have a twist in your balanced two conductor
feed line.
Or you can use quadro or hexo line, which contains the fields even more.
AC power lines do the same thing (periodically rotate the positions of
the phases on the towers/poles). And back in the open wire
telephone/telegraph days, they did the same thing. I've not seen much
open wire phone line recently, but you do see the crossover insulator
things.
For that matter, that's why cat 5 has twisted pairs with different twist
rates.
By the 1940s these devices seemed to have disappeared,
possibly because of the availability and easy installation of coaxial
lines after the war.
Balanced lines are probably of limited use these days:
1) amateur radio
2) fixed broadcast HF stations with high power (feeding a multi bay
dipole array with open wire line is a natural, and low loss, too)
3) high power RF/pulse work over short distances
Paul, W9AC
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