[TowerTalk] 80m 4Square Dipole VSWR question

[Joe Subich, K4IK]

> 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. 

 
73, 

   ... Joe, K4IK