Bill:
This may not be the solution you are looking for....but:
Put both elements back pointing the same direction.
Shorten all the elements on the 20 the same amount to bring it back to
resonance.
The fact that the 20m Yagi has been "loaded down" because of the 40m
does not mean that there will be a problem with the pattern AFTER it is
re-tuned. There IS interaction....but only to the extent that the 20m
elements now resonate lower in frequency. Modeling would likely confirm
this. The same thing happened here when the 80m dipole (or later the
Yagi) was added to the tower at VE6WZ.....the 40 needed to be shortened
but the pattern was preserved. Modeling confirmed this.
40/20m , 80/40m etc. duo-banders are commercially available because they
work this way.
de steve ve6wz. http://www.qsl.net/ve6wz/index.html
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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