Last summer, using spare tubing and tubing from an old 14AVQ I put up a
33-foot 1/4 wave 40 meter vertical. I laid down 32 radials of various
sized with 16 of them being 32 feet long. There is an RF choke at both
the tuner and the base of the vertical. Using this vertical I have
worked 150 countries on 40 meters (my total is 216 since I started over
on 01/01/05). I use a Palstar AT1500CV tuned in the shack and run RG8X
buried to the vertical. I run an IC756 PRO III and a Yaesu FL2100B when
needed. I also run my newly build (3/6/07) K1. I have worked 40
countries and 26 states, 200 QSOs using that vertical. It works great
on 40, 30 and 17. Best on 40 and I can always work anything I can hear
including BY, YB, 4X4, 3Y0, R1, etc. For the money $0.00, who can
complain. See: http://www.metaphoria.us/hamradio/ham_radio.htm And
yes, I need to add a webpage on the new K1 and the four 55-watt solar
panels from which it draws power. :)
Jozef WB2MIC
Wells VT
Stuart Rohre wrote:
Both the half wave and 5/8 wave antennas are complete resonant structures
without the need for radials. See L. B. Cebik's web site, www.cebik.com for
his discussion modeling half wave verticals, and little was gained by
modeling radials under them.
The reflections you are concerned about are in the range beyond the Fresnel
Zone, some 5 or more wavelengths out from the vertical. Short 1/4 wave
verticals need radials to complete the circuit and return RF current to the
feedpoint.
You can feed with a link, and possibly not need the cable choke. But, the
cable choke is good insurance in any case. The whole issue is one of
balance and if the feeder leads off vertically under the vertical, there is
minimal pickup of RF by its outer conductor. Of course, if it is at right
angles to the vertical directly at the feed point, there is more chance of
current reaching the outer conductor inducing unbalance.
An efficient ground for a 1/2 wave vertical is any whose impedance is say
1/10 of the feedpoint impedance of the vertical conductor, which is
typically around 3000 ohms, depending on how close it is to RF earth at the
base of antenna. So, a ground of 300 ohms would work in this case, while it
would way inefficient for a quarter wave vertical, which needs a return
conductors impedance of less than 3.6 ohms or so. (36 ohms base impedance
on theoretical quarter wave vertical, base fed.) You want the ground to be
a much more attractive path for RF than the other impedances in the system.
73,
Stuart
K5KVH
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
