Topband: DX-Enginneering Active Antenna System

[Lee K7TJR]

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