Vertical Antenna tidbits

I have said many times that horizontal antennas give better performance (stronger signals) than vertical antennas at 20 meters and higher frequencies. While that is definitely true, there are times that the strongest possible signal is not the most important thing.

Once a signal is readable or of adequate strength to meet the communications requirement it is frequently of no use to make it stronger. 

Many times a very simple, small antenna with zero dBi gain ( such as a vertical)  or even negative dBi gain ( such as a mobile antenna) will work and satisfy our needs quite nicely.

For those times I will use a top loaded mobile antenna mounted on my truck. Under the right conditions it does not take much radiated power to communicate long distances. While with a good horizontal dipole I might be S-9 plus 10 dB on an S-meter in California, I may still be S-8 with a mobile vertical antenna. The difference is this case is maybe 16 dB. For all practical purposes to make the communications I don’t need to be very strong, I just need to be above the noise level at the receiving station. For most amateur radio operations the chances are that with even a few watts into a small antenna you can be heard somewhere in the world. You just have to pick the right time and frequency. Trying to push the limits of extreme long distance and get through to a rare country will require a better antenna than trying to communicate 300 miles on 40 meters or 1200 miles on 20 meters. Picking the optimum time of day for that 300 mile QSO on 40 meters is just as important as the antenna gain. If you are on at the wrong time it will not matter if you are running 1500 watts and have an antenna 100 feet in the air! Pick the right time and frequency and you can be S-9 plus with 2 watts and a poor antenna!

Let’s one more time think of power. Let’s assume we have 100 watts and we can radiate it is all directions equally. That is almost always the reference we should use. That is 0 dBi or zero dBi.

The closest we have to that signal level is a vertical. Typically verticals radiate a signal at a fairly low angle that is roughly the equivalent strength of an isotopic antenna. The main difference being the isotopic antenna also radiates up and down equally and there are no ground reflections from the isotopic antenna. With real antennas such as horizontal dipoles and vertical antennas there are ground reflections that can both help increase the signal in some directions and hinder it in other directions. When an electromagnetic field radiated from an antenna first strikes the ground the orientation of the electric field ( E field) is very significant. If the E field is parallel to the earth ( horizontal polarization) the reflected signal is reversed in phase. If the E field is vertical it is not so simple. What happens depends on many factors. If the ground is seawater one thing happens, other things happen if it is earth. If it is real earth then the conductivity then makes a large difference. The angle at which the Electromagnetic field strikes the earth is also significant. There is a critical angle called the pseudo Brewster angle that essentially reduces the low angle radiation. All this means is that the simple vertical is not so simple and it’s hard to achieve a gain greater than 0 dBi from a vertical over real earth. Verticals over seawater are possible and are great but there is no such thing as perfect ground even though it is one option in antenna modeling. I always model with programs that allow a simulation with “real ground” parameters.