> From: Paul Playford
> Assuming that the phase shifting box was designed to drive a
> ground plane array this would require the 0 degree port match
> 165 ohms, the 90d port match 82 ohms (two elements in parallel)
> and the 180d port match 165 ohms.
Except the 0 degree port and the 180 degree port are actually
connected in parallel (the 180 degree port is connected to the
zero degree port through a phase reversal transformer/un-un).
Thus, you have the quadrature (90 degree) port and the in-phase
port each seeing 82 Ohms ... which when combined result in a
nominal input impedance of 41 Ohms for the "box."
Of course, all of that does not consider the mutual coupling
among the elements of a four square or ground losses! However,
a four square constructed of verticals (over perfect ground) that
were adjusted for j0 in isolation and spaced 1/4 wave on a side
would show widely differing impedances for the leading, lagging
and side elements. AO shows something on the order of:
Leading element (1) 67.2 +j53
Side elements (2&3) 37.3 -j19.4
Lagging element (4) -1.5 -j12.9
Given the wild mismatches, it would be interesting to see some
measurements of actual current magnitude and phase in a "real
world" four square being fed with a Comtek style box.
... Joe, K4IK
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
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