## Tuesday, March 30, 2010

### Dipole, Inverted V and Ground Plane Antenna Calculators

Dipole, Inverted V and Ground Plane Antenna Calculators

The first online Dipole and Inverted V calculator on the page below has been around for many years and is designed as a simple "shortcut" so you will not have to do the math using the standard formulas for designing a horizontal dipole or inverted V dipole. It's results may be different than what will work at your particular location and your installation. Antenna calculators are not an exact science so don't expect "plug and play" results. It has no way of knowing ALL of the variables in your installation.

As you may already know, no two antenna installations are alike or identical in many ways, even when using identical antennas and each the same height above ground.

The surroundings, height above ground, the ground conductivity, and many other factors can detune most any antenna. Even the length, diameter of wire used, and type of feedline can be a factor to some extent.

Using larger conductor diameters for the antenna like aluminum tubing rather than normally used #12 or #14 AWG wire can have an effect that will be different than using the calculator which is designed for normal wire use.

The old standby formula 468 / freq in mhz = total length is used in the calculator for an average height of 1/2 wave high and horizontal dipole..and then 5 % is subtracted from that number to get the inverted V lengths. These formulas are used to get you close to the desired lengths......but they will result in ONLY the ball park lengths and not an exact length when you take into consideration all of the factors involved with the environment of the antenna.

The calculator assumes that the dipole is high above ground with no obstructions nearby, usually within 1/2 wavelength above ground or higher.
Always when using "formulas" or calculators...cut long and then tune as needed....the calculator is used just as a starting point and depending on the environment under, on top of and on both sides of the antenna, and the "specs" of your materials used, your actual final lengths may be different than what the calculator shows.
The calculator does not give you EXACT lengths that are "plug and play".
It does not know ALL of the variables with your installation.

Antennas can be much fun to work with even when using an antenna analyzer that will show you what happens when you make changes. If you do have an antenna analyzer then you have an advantage over many others that do not have one. They have to use the old "cut long and then trim down" method even when using the calculator or the so called "formulas".

You can "plug in" different angles of the V and get the results for each angle:

Use 5% for 45 degrees (The calculator should already be set for 5, if not change it to your desired angle using ONLY the percentages below. The results will still be "in the ball park".
Use 4% for 37 degrees
Use 3% for 30 degrees
Use 2% for 22 degrees

Enter The Frequency For The Dipole/Vee Antenna Calculation
Use entries like 7.200, 7.2, 144.200, 144.225, etc...

Divided by Freq MHz

Percent smaller for the Inverted Vee
Your dipole's total length is feet
Each leg of the dipole is feet
Your Inverted Vee's total length is feet
Each leg of the Inverted Vee is feet

The picture above is a diagram of the old standby CLASSIC antennas....the Dipole and the Inverted Vee. They are shown 'together" in the drawing for ease of viewing on this page.

The horizontal dipole and inverted V are shown superimposed on each other in the drawing and without the feed line for clarity. It is assumed that you understand that we are talking about 2 separate antennas in the drawing and not one antenna with 2 bands fed with coax.
Feed line (usually 50 ohms) is connected at feedpoints, center conductor to one side, the shield to the other side of antenna. The blue line in the drawing is the example of a horizontal dipole. The copper colored line is the inverted vee configuration. The inverted vee is is just a lazy dipole that can't hold it's arms up and is about 4 to 5% shorter in its total length. 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 a tuner. When fed with open wire type feed, it becomes a multiband antenna using a tuner. The use of an rf choke is recommended when using coax feed!
The inverted V antenna more closely matchs the 50 ohm coax than does the standard horizontal dipole, so your swr may be lower compared to a horizontal dipole fed with the same 50 ohm coax.
You could use the calculator to build a 75 or 80 meter dipole and then calculate an inverted vee for other bands higher in frequency, suspended under it as shown in the drawing above, from the same support and feed both with the same line to xmtr. This is usually called a "fan" dipole and works well when tuned for lowest SWR.
A little experimentation may be required for adjustment of the SWR, tuning the 75 meter dipole first for lowest SWR and then the inverted Vee/s under it in a test, cut, test, cut fashion.

Courtesy of and designed by
N2IMF
Joseph R Mielko
This downloadable calculator will provide you with good starting measurements for a basic ground plane, Inverted V or standard Dipole antenna.

The graphics below are "screen shots" taken from it. Non functioning!

Basic Ground Plane Calculator screen shot.

Dipole and Inverted V screen shot of calculator.

This is a very simple program to use and has a handy "Print" function and nice graphics showing the basic layout of each antenna.

All you have to do is run the program and input your design frequency in the white window top left. Click "Calculate" and the length results are shown in your choice of feet or inches.

You may be surprised at how fast it works!

It is not a large file and should download quickly for dialup users.
After the file unzips, open up the folder and look for the "N2IMF antenna.exe file...double click it and the program comes up! Enjoy!
Again, this calculator is courtesy of N2IMF...Thanks Joe!

EXPERIMENT! EXPERIMENT! EXPERIMENT!