An 80-meter Ground-mounted Vertical Antenna Design
By Rob L. Dey  KA2BEO  9/13/94

Specifications
Antenna description: 22' base-loaded 80M vertical up 8'.
Center frequency: 3.75 MHz.
Frequency range: Useable from 3.5 to 30 MHz (MUF = 31.8 Mhz) by moving coil
                 taps.
Ground radials: 2 copper wires 56' long #18 AWG 1" below ground.
                6' of structure is seated into the ground.
Radiator length: 22' 1" (265" or 22.08333'), 30.3 electrical degrees
                 @ 3.75 MHz. 1/2 wavelength @ 21.2 MHz.
l/d ratio: 385 average.
SWR: 1.6:1 w/o coil (Lm), 1:1 w/ coil (Lm).
Efficiency: 6-10% (less than 1 S-unit below the signal of a 1/4 wave vertical).

Features
DC-grounded design eliminates static build up.
All aluminum and stainless steel construction resists corrosion, even in harsh
 environments.
Low-angle radiation pattern offers long-distance communication.

System Parameters

fo = 3.75 MHz
Rr = 2.94 ohms
Ca = 75 pf*
Xc = 565.9 ohms
Za = 2.94 - j565.9
Zo = 52 ohms
l = 265"
d = 0.6875" average*
h = 30.3 degrees (0.084 wavelength)
Rf = 31 ohms*
Xs = 25.5 ohms
Xp = 63.2 ohms
Ll = 24 uH
Lm = 2.68 uH (2.7 uH)
Ka = 0.97*
w = 23561944.9

* = value estimated

Part Descriptions (Most parts are from an old 1/2-wave CB ground plane antenna)
1 Alum. tubing 1/4"od, 4'long, insert 16" (32" exposed)
1 Alum. tubing 3/8"od, 4.5'long, insert 4" (1/8" hole @ 3.5") 2 slots 3/4"long
 at other end (50"x)
1 Alum. tubing 5/8"od, 4.5'long, insert 11" (1/8" hole @ 10.5") 5/32" hole @
 0.5" fluted end (43"x)
1 Alum. tubing 3/4"od, 4.5'long, insert 10.5" (1/8" hole @ 10") 5/32" hole @
 0.5" other end (43.5"x)
1 Alum. tubing 1-1/8"od, 4.5'long, insert 10.5" (1/8" hole @ 10") 5/32" hole @
 0.5" fluted end (43.5"x)
1 Alum. tubing 1-1/4"od, 4.5'long, insert 1.75" (1/8" hole @ 1.5") 5/32" hole @
 0.5" other end (52.5"x)
1 Alum. tubing (base) assembly 1-7/8"od, fiberglass and plastic base with
 SO-239 connector
1 Alum. tubing (mast) 1-5/8"od, 10'long, insert 4' (1/4" thru holes @ 3.5' &
 2.5') 2 holes at other end too
1 Galv. steel post (ground mounting rod) 1.9"od, 1.7"id, 8'long, insert 6'
 (1/4" thru holes @ 0.5' & 1.5')
4 S/S #6 1/2"long sheet metal screws
1 S/S 3/8"dia. hose clamp
2 S/S #1/4-20, 1"long bolt, with S/S: lock washer
2 S/S #1/4-20, 2-1/2"long bolt, with S/S: flat washer, lock washer, and wing
 nut
1 Coil (Ll+Lm) 25.5uH 30 turns, #12 AWG, 6 TPI, 5" long, 2.5" dia. Q=300 B&W
 #3029
2 Copper wires 56' long #18 AWG
1 Rubber cap <1/4"id 1"long

Miscellaneous
Total radiator length (inches) = 36-4+54-4+54-11+54-10.5+54-10.5+54-1.5+0.5
                               = 265"
Average diameter (inches) = (.25+.375+.625+.75+1.125+1.25)/6 = 0.729167"
Average l/d ratio = 363


An 80-meter Ground-mounted Vertical Antenna Design
By Rob L. Dey  KA2BEO  9/13/94

Final Results
The antenna is mounted 31" x 31" from the corner of a 6' tall wooden fence.
SWR: <1.5:1
BW (2:1 SWR): 400 kHz, 3.5-3.9 MHz
Coil: 46 uH 42 turns, #18 AWG, 14 TPI, 3" long, 2" dia. Q=300 #6033 ceramic
Ll = 26.2 uH tapped at 32 turns from ground end
Lm = 8.8 uH tapped at 8 turns from ground end
Note: Ll was set with a grid dip meter, and Lm was set with an RX noise bridge.
 Further "on-air tweeking" could improve the SWR and usable BW.