Oops, my bust I guess. Damn computer programs! Well, I probably
should have stated that this should be "tried at your own risk". I
guess that my point was that it should be possible to steer a signal by
using crossed dipoles. We do it at ELF frequencies for submarine comms,
so it should work at any other frequency as well...just takes a little
dinkin' around...but hey, that's what autotuners are for

Scott
N0EDV



Cecil Moore wrote:
Cecil Moore wrote:

acepilot wrote:

As long as you use resonant dipoles, current and voltage will be in
phase in its respective dipole, so the impedance will not change.



This isn't always true. The feedpoint impedances of two resonant
dipoles when phased together are not usually resistive. For instance
using EZNEC:

A 33 ft. dipole at 66 ft. has a feedpoint impedance of 70+j0 ohms
on 7.298 MHz.

Two 33 ft. dipoles at 66 ft. spaced 33 ft. apart and fed 90 degrees
out of phase have the following feedpoint impedances on 7.298 MHz:

109+j34

29-j33

Please describe how you would achieve equal magnitude currents 90
degrees apart into those dipoles given those feedpoint impedances.


I just ran this matching problem through Roy's (W7EL) SIMPFEED BASIC
program downloadable from http://www.eznec.com

Using 300 ohm twinlead, the program said that one feedline should be
27 degrees and the other should be 168.5 degrees. For 7.298 MHz and
VF=0.9, that's lengths of 9.1 ft. and 56.78 ft. I plugged them into
EZNEC and it worked great - a phased dipole array with 10.5 dBi gain
in one direction. The above lengths ensure that equal currents flow
in both elements and gives a 50 ohm SWR of about 2:1 at the junction
of the two 300 ohm feedlines.

Incidentally, there were no solutions using 50 or 75 ohm coax.