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AMATEUR RADIO - DIPOLE CONVERSIONS

INTRODUCTION - The longwire antenna is a very effective antenna for the listener who wants to cover all of the shortwave bands from 530 Khz to 30 Mhz. However if you have some favorite frequencies that you listen to on a regular basis you may wish to consider a dipole antenna. This antenna is a fairly easy to construct antenna and will give you better reception on the frequency that it is cut for. Think of a dipole as a longwire that has an insulator in the middle.

FREQUENCY - A dipole antenna will not only work well on the frequency that it is cut for, but also for the multiples of that frequency. For example if you cut a dipole for 7.0 Mhz will also work well on 14 Mhz, 21 Mhz and 28 Mhz. This way if you can pick and choose your frequency you can make one antenna work on two or three bands.

LENGTH - To find out how long the antenna should be all you have to do is fill in a simple formula:

Instructions for Use:
  • Enter the frequency for the Dipole &/or Inverted "V" Antenna Calculation
  • Use entries like 7.200, 3.5, 50.140, 442.200, 147.045, etc...
  • Press the "CALCULATE" button for results.

Divided by Freq. MHz

smaller for the Inverted "V"

   

DIPOLE RESULTS
Your Dipole's TOTAL length is: feet
Each LEG of the Dipole is: feet
 
INVERTED "V" RESULTS
Your Inverted V's TOTAL length is: feet
Each LEG of the Inverted "V" is: feet


The picture above is a diagram of the old standby CLASSIC antennas... the Dipole and the Inverted "V" antennas.

They are shown superimposed on each other in the above representative drawing.

The BLUE colored line is the dipole configuration.

The COPPER colored line is the inverted vee configuration.

The Inverted-V is basically a straight dipole broadband antenna with high gain that requires a little less space than the straight dipole and requires only one long mast at the center. The base, or bottom of the 'V' is connected to the top of the mast. The end of one arm of the Inverted-V is connected to ground via a terminating resistance, while the other end of the second arm is connected to the antenna feeder. The Inverted-V antenna is an excellent antenna for static locations. On flat ground the Inverted-V antenna radiates mainly surface waves, but can be used to generate space wave if erected on a hill.

Both antennas can be constructed just about anywhere using any type of wire you may have and can be used with 50-75 ohm coax or open wire ladder line and an antenna tuner. The use of an RF choke balun is highly recommended. Most antenna critics agree there is little difference in the performance of either the Inverted-V and the straight dipole. The largest difference between the two antennas is the length of wire needed. Inverted-V's usually require about a 5% shorter wire length per leg than the straight dipole.

You could use the calculator to build a 75 meter dipole and then calculate an Inverted-V for other bands suspended under it from the same support and feed both with the same line to your transmitter. A little experimentation may be required for adjustment of the Standing Wave Ration (SWR), tuning the 75 meter dipole first for lowest SWR and then the Inverted-V.

LENGTH CONVERSION FACTORS
CONVERT FROM TO MULTIPLY BY
mile (US Statute) kilometer (km) 1.609347
inch (in.) millimeter (mm) 25.4 *
inch (in.) centimeter (cm) 2.54 *
inch (in.) meter (m) 0.0254 *
foot (ft.) meter (m) 0.3048 *
yard (yd.) meter (m) 0.9144 *

Amateur Bands
160 Meters

MHz "L" (Feet) "E" (Feet)
1.800 260.00 130.00
1.900 246.32 123.16
2.000 234.00 117.00
80 Meters

3.500 133.71 66.86
3.600 130.00 65.00
3.700 126.49 63.24
3.800 123.16 61.58
3.900 120.00 60.00
4.000 117.00 58.50
60 Meters

5.331 87.80 43.90
5.347 87.53 43.77
5.367 87.21 43.60
5.371 87.13 43.56
5.404 86.61 43.31
40 Meters

7.000 66.86 33.43
7.100 65.92 32.96
7.150 65.45 32.73
7.200 65.00 32.50
7.300 64.11 32.05
30 Meters

10.100 46.34 23.17
10.150 46.11 23.05
20 Meters

MHz "L" (Feet) "E" (Feet)
14.000 33.43 16.71
14.100 33.19 16.60
14.200 32.96 16.48
14.220 32.91 16.46
14.300 32.73 16.36
14.313 32.70 16.35
17 Meters

18.068 25.90 12.95
18.130 25.81 12.91
15 Meters

21.000 22.29 11.14
21.100 22.18 11.09
21.200 22.08 11.04
21.300 21.97 10.99
12 Meters

24.890 18.80 9.40
24.950 18.76 9.38
10 Meters

28.000 16.71 8.36
28.500 16.42 8.21
29.000 16.14 8.07
29.500 15.86 7.93