[TowerTalk] Antenna interaction tests

[K4SAV]

The consensus for placing a 4 element SteppIR and an XM240 five feet 
apart is that this is much too close. Although it is true that the 
SteppIR can be retuned to lower the SWR because of interaction, you 
probably wont be able to recover the loss in gain or F/B.

Thanks to Joe, K4IK for modeling this configuration and modeling some 
possible solutions.  Modeling shows with 5 ft seperation, on 17 meters 
the SteppIR loses 3 dB gain and most of its front to back.

Possible solutions:

1.  Turn the antennas 90 degrees to each other

2.  Place antennas 5 ft apart and disconnect the feedline (center and 
shield) from the XM240 with a relay located at the feed point.  (Loses 
1dB gain, 6 dB F/B on 17M, and loses 0.5 dB gain, no F/B loss, on 15M)

3.  Place antennas 5 ft apart and use an odd multiple of 1/4 wavelength 
on 17 meters feedline, to the XM240 and short line when using the 
SteppIR. (Loses 1 dB gain, 6dB F/B on 17M, and loses 1 dB gain, no F/B 
loss on 15M)

4.  Buy a new mast which will allow 10 ft seperation. (Another month 
wait for delivery and >$500 expense) This solution in combination with 
using the "odd multiple of 1/4 wavelength on 17 meters feedline to the 
XM240" loses only about 0.2 dB gain and 0.5 dB F/B, - insignificant.

Thanks to all who replied
Jerry K4SAV