sounds like a lot of joints that could slip. i wouldn't expect a lashup
like that to survive very long up here in ice and wind country. i would
get rid of the '1 1/4" posts sticking up' and mount the quads right to the
cross arm. and unless that extra 6' really is necessary i would mount the
crossarm directly to the steel mast. which way are these going to be
polarized, horizontal or vertical?? even if vertically polarized they
should be ok being 2' out from the steel mast i would think.

"ab5mm" wrote in message
...
Thanks to Tom, Dave and the rest of you that answered my question so
quickly.

I thought I should give a little more pertinent info on this project. A
elderly ham friend of mine is putting together a 70cm fast scan TV
station. He chose the quad because of its wide band characteristics. His
tower is Rohn 45 at 73 feet. It has a Glen Martin "Voyager" trolley/tram
system. The steel mast is above the bearing plate about 14 feet. Out the
top of the steel mast is 6 feet of thick wall fiberglass tubing. The two
70cm quads will be on a fiberglass cantilever arm that is approximately
48" long. It slips over the fiberglass mast and bolts into place. (arm
required to clear the tower when cranking antenna system down) This arm
will have two, 1 1/4" diameter post sticking up vertically to mount the
quads. Here is where the question arose about how far apart the quads
should be.

I don't think I could/should push the cantilever arm out any further.
The system, all together, could probably withstand a little longer arm
if required. ?? Three 1/2 wavelengths would be ~39 inches.

The quads are 7 1/2 feet long with 12 elements each and weigh 3.5 pounds.

We have no modeling software, just a desire to do it right the first time.

Thanks again & 73,

Steve
ab5mm