The more the merrier, 30 minimum. Length not that
critical but 1/4 wavelength at 130 ft. is theoretical
best. Most recommend 60 radials and broadcasters go
with 120. Last year I have about 30 down (put up shunt
feed last Feb. and laid the radials on the ground).
This year, after the last grass cutting, I plan on
permanently putting in about 30 to 45. However, with
the match connected to just the tower base, which is
well grounded with three ground rods per leg, the tower
seems to be working well. Phil KB9CRY
> Aren't radials also needed to make the shunt fed tower work efficiently? If
> what would be the correct length and how many for a respectable installation?
> Julio, W4hy
> > Jim:
> > 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
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