Direct email failed, but perhaps others are interested anyway. Here are
my comments:
Sounds like a lot of work, but I'm still jealous! (I have a single 70 foot
tower on a 60 X 120 foot city lot. But at least I have a very short
commute to work.)
I'd go for the extra height for the 40 M tower. 76 feet is marginal for
40, close to optimum for 20. Also, if you can orient your towers
right, you could stretch a 2 element 80 M wire beam between two of
them. Feed it with open wire, and also run open wire from the parasitic
down near the ground to a box with relays and a tuning network. That way
you can make it reversible (EU/Pacific), and also get it to work all
over the band. The tuning is easiest if the open wire is a half wave
long on the parasitic, but it should work with shorter lengths if you
use the right reactance in the box. K6NA uses such an antenna, with
obvious success.
With your 10/15 M beams up so high, you will want to have lower beams
available. Even at 70 feet, I sometimes get beaten out by locals
with smaller antennas at 40 feet or so, apparently when the vertical
angle lands right in my null. (About 13 degrees on 10.) Check out
the vertical patterns in the Antenna Book, and make sure your lower
beams are at the right height to fill in the null of the upper
ones. (Offhand, it looks like you're pretty close.) Of course,
feeding the beams so you can choose either, or both, gives you
lots of flexibility. Make the switching convenient, so you can
quickly pick the combination that works best at the moment.
Good luck!
73,
Scott Ellington, K9MA
sde@sal.wisc.edu
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