I forgot to add: two shortend, elevated radials, fed as described below,
is only slightly poorer (about 1 dB) than four.
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
.
On 26/08/2020 14:36, Victor Rosenthal 4X6GP wrote:
Kevin,
My advice is to get Moxon's book, "Wire Antennas for All Locations."
Follow his advice, which is (roughly): use four elevated radials at a
level higher than an Elk's antlers. Make the radials equal in length,
about 0.15 wavelength long, connect them together, and add an inductance
in this common ground lead to resonate them. This helps equalize the
currents in the radials, which keeps your radiation angle low.
Do not use buried radials unless you have room for at least 16 of them.
In that case they can also be about 0.15 wl long.
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 26/08/2020 3:31, kevinr wrote:
I have to be very careful of raised wires on my property. If they are
not above the height of an elk's antlers I am in trouble. I plan to
bury them. This is something I've never done before which has its own
merit. I have plenty of wire scrap from broken antennas so the
non-resonant, buried radials work better for my circumstances. I need
to calculate the feed point impedance to see if I need to design a
balun for the system to work. Once my main project is done I'll have
more time for modeling each method.
Thanks for all the ideas guys,
73, Kevin. KD5ONS
On 8/25/20 5:23 PM, Wes wrote:
You probably should get acquainted with Rudy Severns, N6LF.
(https://www.antennasbyn6lf.com/) He has written more than you ever
want to know about vertical antennas,
More specifically to your case, are you planning the radials to be
elevated? If so, they need to be the same length, in fact some
effort should be made to get all of the currents the same. The last
thing you want is a fifty ohm feedpoint impedance with a shortened
vertical (which is what an L is). There is evidence that elevated
radials are an improvement over on-the-ground or buried radials.
Mine are on the ground, mainly because 1) I didn't want to give up
radiator height to raise the radials, 2) all of the big guns bury
theirs and I don't have room for full length radials anyway in my
cactus patch. See my QRZ page for evidence.
My modeling shows a little bit of directivity away from the
horizontal wire, but it's negligible.
Wes N7WS
On 8/25/2020 4:23 PM, kevinr wrote:
From what I can find, and what I can calculate, five wires, each
~130 feet long, could make a nice inverted L for 160 meters. One
leg for the vertical and horizontal portion of the antenna. Four
legs for the counterpoise (ground plane). There are many broken
wire antennas stored in my shed which are fodder for the radials. Do
all of the legs for the counterpoise need to be 1/4 wavelength or
can I substitute some shorter lengths? The feedpoint should
somewhere above 50 ohms impedance. As I add more radials that
number will reach 50 ohms asymptotically.
I can get the vertical part up to 70 or 80 feet above ground with
the rest of it horizontal. Most of the radiation should take place
from the vertical part since it is closer to the feed point. But
there should be some effect from the direction of the horizontal
portion. How strongly does the direction of the horizontal portion
effect the radiation pattern of the antenna system? My property
allows me to point it from 300 degrees around to 200 degrees so I
have plenty of options. Between 200 and 300 degrees there is a road
used by loggers, and the folks maintaining the towers at the top of
this mountain. They can break any antenna lower than 80 feet above
ground. Spar poles and cranes clear out any dead limbs across the
road.
Inquiring minds...
Kevin. KD5ONS
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