[TowerTalk] stacking 4X 15m beams

[Texas RF]

Ah ha! A subject that I like to talk about: stacking beams (sells more
aluminum don't you know).

As many of you know, the good 75 ohm coax is becoming harder to find unless
you are one of the fortunates with access to catv scraps.

Four way power division is easily done with all 50 ohm cable on this manner:
1> Use four equal length 50 ohm lines from the antennas back to the center
area of the array. It does not matter if the stacks are vertical, horizontal
or a combination.

2> construct a four way 1/2 wave power divider of 50 ohm coax with a tee
connector at the center and on each end. (Don't forget velocity factor). This
actually constitutes back to back 1/4 wave lines.

3> connect one antenna to the ends of the tee connectors and feed the tee
connector in the center.

For those not understanding how this works, the principal is based on the
impedance inverting characteristic of a 1/4 wave line. Two of the 50 ohm
antennas are connected in parallel by a tee connector, producing 25 ohms. The
50 ohm 1/4 wave of coax will transform this value to 100 ohms. The two 1/4
wave lines are connected in parallel by the center tee connector, producing a
load of 50 ohms again. Four way power dividers built this way have extremely
low vswr and are very wide banded.

This scheme is used extensively on vhf/uhf and will work equally well at hf.

Tnx/73 de Gerald, K5GW, General Manager, Texas Towers

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