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Rotatable Delta Loop for receiving on 160M and 80M. Measures 17 ft.
tall by 28 ft. long. All home brew, designed by Earl Cunningham, K6SE
(k6se@juno.com), fiberglass poles by Max-Gain Systems (tnx to Allen Bond
of MGS).
All from Earl's article from July, 2000 QST.
The delta shape was chosen since it is the most sturdy; here near
Chicago, the antenna will get a half inch of ice on it along with high
winds and I wanted something that would survive that. The frp poles
also are the most sturdy, non-conductive available for a reasonable
price. The mast is made of 1-1/2 and 1-1/4 inch poles and the cross arm
is made of 1-1/4, 1 inch, and 3/4 inch poles, all nest within each
other. Very sturdy; similar to MGS's quad spreaders that they offer.
The antenna is mounted on a single old Rohn BX tower section which is
lashed to a fence post. The bottom therefore is eight feet off the
ground; so I can walk and drive the tractor beneath it and not bang my
head! The rotator is a Dayton Flea Market Channel Master special; I
picked up two for 30 bucks with the thought, "I'll find a use for these
someday..."
Home brew xfmr, 8 turns coax side, 28 turns (for 75 ohm RG6 coax) loop
side on Amidon FT-140-43 (pre wrapped with TFE tape and Q-Dope applied
afterwards for weather protection), 0.01 mf @3Kv disc cap in line with
coax for DC blocking. 9 total watts of 947 ohm terminating resistor. 14
AWG hard drawn non insulated wire. Have since changed coax loop choke
seen in some piks to 12 inches of Amidon F-50A-J toroids (the coax loop
was too heavy and was pulling on the FRP mast) on the coax. You can see
these in other piks. The xfmr and resistors are housed in Radio Shack
plastic project boxes which are cable tied to the ends of the cross
arms. The wire rests in a notch cut in the top of the mast and is
connected to the boxes at the ends. The bottom wire is simply
taped/cable tied to the cross arm and cable ties, again, pull it away
from the mounting plate at the center. The coax is hung below the cross
arm with large cable ties, about 10 inches, and a very large loop is
made at the center to allow for rotation. If you look closely, you'll
also see the two inner dacron rope (3/16 dia.) spreaders which help hold
up the cross arms; this was done to take stress off the wires coming
down from the top. Finally to answer some folk's question, the bolt in
the bottom of the xfmr is not a ground connection; there is no ground
connection. That's an assembly error, I drilled the coax fitting hole
in the wrong place and used the bolt and nut to cover the hole to keep
out the bugs Each box does have a small drainage hole in the bottom.
Click on a picture for larger size.
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