W4TV says:
<The "phasing" part of the W8JI design was on Tom's web site for
a very long time. The design is not too difficult for a good
home builder. The most complex parts are the transformers and
anyone who has built their own Beverage units will have no
problems. >
Yes, the time delay phasing (crossfire) has been disclosed for a very long
time on Toms
website. There is more than one way to accomplish phase tracking with a 4
element
array. I cite Rick N6RK and his cross element source inversion among others.
Using active amps is a little more complicated than loaded elements in an
array controller.
One cannot use the simple early design of W8JI to combine active antennas. That
design used simple cable paralleling for signal combining and as such will
provide
a very low impedance to the active amps. I am not aware of any active amps
designed
to drive 25 ohms or less. That W8JI controller relies on the impedance of the
loaded antennas to exactly match the connecting cables so that the phase delay
cables
will have at least one end terminated in its correct impedance. Without one end
of the cable being
correctly terminated the phase delay is NOT the same as it is terminated. Except
at 90 and 180 degrees which is generally not used in an RX 4 square.
In my opinion one must use hybrid or magic tee type combiners to assure the
active amps
will maintain there designed IMD performance while looking into their designed
load impedance.
One must also insure the time delay through each channel of a controller is
the same which
may be a little more difficult for home builders. Especially if they are
contemplating a narrow spaced array.
Lee K7TJR OR
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