This is a deviation from the wonderful antenna the Double Bazooka. I was in need of a good antenna for field use and with minimum support requirements. So this is what I came up with.
The Vertical element is still a 1/4 wave so from the center feed point to the top is found by the simple and well known formula 460 / Frequency in Mhz then Divide it by 2. This will give you the Total length of the Vertical element.
Now for the Vertical Coax part "A" use the formula 325 / Frequency in Mhz divided by 2. Then add about 4 inches to tie in the Radials and the center conductor on the lower end with the Shield on the Feed line.
Now for the top portion of the Vertical "C", Take your 460 / Frequency in Mhz minus the length of B (325 / Freq) and divide it by 2. That will be the length of wire added to the top section of the vertical.
For the Radials use the Formula 460 / Frequency in Mhz and Divide it by 2 and then Multiply by 1.05. That will give you the total length of your Ground Radials. I use 4 but you only need 2 for this antenna to work well at a minimum. Keep adding the Radials to improve your Omni Directional signal.
Vertical Total (A + C) = 460 / Freq in Mhz divided by 2
A =Vertical Coax = 325 / Freq in Mhz divided by 2 + 4 inches (for lower Radials to tie in)
B = 325 / Freq in Mhz
C = Vertical Top Wire = 460 / Freq – (325 / Freq) and divide by 2
Radials = 460 / Freq in Mhz divided by 2 X 1.05
I was amazed at the first one of these I built, I only trimmed about one inch off of the top to move the 1.0 to 1 SWR from the 14.050 on up to the 14.150 and it is better then 1.3 to 1 across the rest of the band so there will be no tuner needed for this one. Perfect for portable or backpack use.
I used tent stakes to hold the radials out on the ground and raised the vertical element to full length over a tree limb and then hooked up the Yaesu FT817 and called out to get a 59 from K4IQ on 2.5 watts from Clarksville, TN to Virginia so I am very happy with it.
Note:
"A" is Coax RG58 or RG8x
"C" and "Radials" are 12 or 14 gauge Copper insulated wire
I use 1/2 inch PVC pipe with caps for insulators and center feed point
3 or more Radials recommended but will work with only 2
40 meters
A = 325 / 7.000 = 46.4 X .5 = 23.2 + .4 = 23’ 6"
B = 325 / 7.000 = 46’ 4"
C = 460 / 7.000 = 65.7 – 46.4 = 19.3 X .5 = 9’ 7"
Radials = 460 / 7.000 X .5 X 1.05 = 34’ 5"
20 meters
A = 325 / 14.100 = 23.04 X .5 = 11.52 + .4 = 11’ 9"
B = 325 / 14.100 = 23’ 1"
C = 460 / 14.100 = 32.60 – 23.04 = 9.56 X .5 = 4’ 8"
Radials = 460 / 14.100 X .5 X 1.05 = 17’ 1"
15 meters
A = 325 / 21.200 = 15.33 X .5 = 7.5 + .4 = 7’ 9"
B = 325 / 21.200 = 15’ 3"
C = 460 / 21.200 = 21.70 – 15.33 = 6.37 X .5 = 3’ 2"
Radials = 460 / 21.200 X .5 X 1.05 = 11’ 4"
10 meters
A = 325 / 28.300 = 11.48 X .5 = 5.74 + .4 = 5’ 11"
B = 325 / 28.300 = 11’ 5"
C = 460 / 28.300 = 16.30 – 11.48 = 4.82 X .5 = 2’ 4"
Radials = 460 / 28.300 X .5 X 1.05 = 8’ 6"
6 meters
A = 325 / 51.100 = 6.36 X .5 = 3.18 + .4 = 3’ 6"
B = 325 / 51.100 = 6’ 4”
C = 460 / 51.100 = 9.0 – 6.36 = 2.64 X .5 = 1’ 3"
Radials = 460 / 51.100 X .5 X 1.05 = 4’ 7"
2 meters
A = 325 / 145.100 = 2.24 X .5 = 1.12 + .4 = 1’ 5"
B = 325 / 145.100 = 2’ 3"
C = 460 / 145.100 = 3.2 – 1.5 = 1.7 X .5 = 9"
Radials = 460 / 145.100 X .5 X 1.05 = 1’ 7"
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Craig McVey, AB8DY, is in the US Army and operates from the field frequently. He is a gifted creator of antennas.
ab8dy@hotmail.com
