## The Underrated Inverted V Antenna

The inverted V is an excellent antenna!—*if it is properly tuned and matched. *This article shows the merits of the inverted V, and includes methods of matching and tuning that antenna. The lesson applies to any antenna.

#### Easily Modified

Many Hams think of the inverted V as a second class antenna, one that happened because some one only had one pole to support a dipole. The real truth is that by bending the dipole the radiation pattern can be modified and the antenna can be properly matched to the feed line. For this article, the design was done at a frequency of 3.9 MHz. Results on other bands will be similar. The antenna patterns and other data are based on calculations from MININEC (a USN CAD program). Tests performed on actual antennas have verified the calculations.

For comparison, **Figure 1** displays the antenna pattern of a horizontal dipole at a height of 1/4 wavelength above real ground. For the purpose of calculations, a dielectric constant of 12 and a conductivity of 0.002 mhos per meter is used. The ground under your antenna may be different, but not enough to make a significant difference in the radiation pattern, unless your antenna is over water. All future articles for *antenneX* will use these parameters. The dipole pattern is a standard of comparison. Two patterns are presented on the same plot: One in the plane of the dipole and one broadside to the dipole.

###### Antenna Pattern for a horizontal Dipole 1/4 wavelength above average Ground at a frequency of 3.9 MHz

#### A Look at the Pattern

**Figure 2** displays the pattern of an inverted V with the apex at a height of 63 feet (almost 1/4 wavelength at 3.9 MHz). Note that the gain of the antenna at high angles is the same as a dipole. At very low angles the broadside pattern is slightly less than a dipole. The lesser energy in that direction means that there is more in the plane of the antenna. In other words, the inverted V is less directional than a dipole at low angles. Now you understand why the inverted V is a preferred antenna for rag chewing on 80 meters.

###### Antenna pattern for a properly tuned & matched Inverted V

with the apex at a height of 1/4 wavelength over ground at 3.9 MHz

#### Poor Reputation

The primary reason the inverted V has a poor reputation is because this antenna is not properly constructed, which means it is not matched and tuned. Figure 3 presents the feed point impedance of the antenna (at resonance the impedance is the sum of the radiation and loss resistance) as a function of the bend angle. For this case, the wires are both in the vertical plane, but have had excellent luck with various configurations including one wire being horizontal and the other at some angle to cause the proper matching. There just isn’t room in the magazine to present all the patterns for all possible combinations.

###### Feed point impedance of an Inverted V as a function of angle Ø

#### Angel is Important

The important point is that the angle between the wires will have a significant effect on the feed point impedance. From Figure 3, notice that the impedance at an angle of 0 degrees (which is a horizontal dipole) is 78 ohms for this particular antenna. As the angle decreases, the impedance is reduced. Notice, at 38 degrees, the impedance is 50 ohms, The impedance does not change rapidly, so you don’t have to be exactly at the right angle to get a pretty good match.

#### Tuning the Antenna

Every antenna installation is unique, due to the surrounding objects, which requires each antenna to be tuned and matched when it is in the operating configuration. To tune an antenna, you need test equipment. The preferred item is an Antenna Ohm Meter. An Antenna Noise Bridge is the second choice, and a VSWR bridge is next in line. Using any of these, determine the resonant frequency of the antenna. If it is different than what you want, change the length of the antenna to bring it close to the desired frequency.

#### Configuring

Measure the impedance of the antenna at resonance. If it is other than 50 ohms, change the angle of the wires until it is close to 50 ohms. Unfortunately, when you move a wire, the resonant frequency will change. Figure 4 was plotted to show the amount of change to be expected. Bending the wires from horizontal to 38 degrees only resulted in a change of less than 150 kHz. Note that as the wires are brought closer together the frequency increases.

If you change the wire length, the impedance will change. Some trial and error will eventually result in an antenna that is resonant at the desired frequency and has a 50-ohm feed point impedance. The next step is to measure the VSWR bandwidth of the antenna. That is done simply by finding the frequency (by tuning the transmitter) that results in a 2.0:1 VSWR on either side of resonance, then subtracting the lower frequency from the higher frequency. This is the useful band-width of the antenna unless you use an antenna tuner to keep the transmitter happy (low VSWR).

#### A Disadvantage

One disadvantage of the inverted V is that it has less bandwidth than a dipole. The example dipole had a 3-dB bandwidth of 347 kHz while the inverted V had only 257 kHz. You don’t get something for nothing. (In a future article I will explain the relationship of 3-dB bandwidth and VSWR.)

#### Summary

If you have an inverted V that isn’t used much because you had poor luck with it, tune it up and let us know how much the performance improved. Be sure you feed the inverted V with a good 1.0:1 balun. If you don’t have a good antenna on the low bands, this one comes highly recommended.

Originally posted on the AntennaX Online Magazine by Ted Hart, W5QJR

*Last Updated : 28th April 2024*