Aren't radials also needed to make the shunt fed tower work efficiently? If so
what would be the correct length and how many for a respectable installation?
> I agree with Phil's recommendations on Jeff's book. You can get it
> from ARRL. I based my Trylon 64's shunt feed on Jeff's design. The key is
> to have something as a capacitive load at or near the tower top to make the
> tower appear electrically longer than it is physically. Your Yagi/40M
> add-on ought to be a pretty good load.
> Many on this reflector would recommend modeling, but I'd say try it and
> let us all know. The feed is nothing more than a wire from the bottom of
> the tower and connected near the top, keeping it a couple of feet away from
> the tower itself (I used PVC tubing as spacer material). Then you feed the
> bottom of the wire through a variable transmitting cap of some fairly large
> value in series with the coax center; I keep the cap insulated from ground
> by mounting it in a plastic weather enclosure (a plastic shoe box from
> K-mart). The coax shield gets connected to the tower legs and ground
> radials. Tune the cap for min SWR and call CQ.
> BTW, the sloper might have an impact on your ability to shunt feed the
> tower. If you can't get the tower to load, you might want to remove the
> sloper and try again. (I haven't modeled this, so I'm guessing.)
> GL es 73 de
> Gene Smar AD3F