Don’s Antenna talks by N4DJ

  Yagi vs dipole My full size 4 element 20 meter Yagi was a good antenna at 70 feet. However it only had a gain of less than 2 S-units over a dipole at the same height. Its elevation angle profile would be the same as the dipole at the same height. Most likely its gain was about 2 dB less than two S-units. A properly installed 4 element Yagi has a gain of about 10 dB over a dipole while 12 dB is two S-units. Under some conditions that is a lot. However under good conditions, signals can be S9 or better and it’s hard to tell the difference by ear. When DX stations are weak and right at the noise level, only one S-unit can make the difference. For general amateur use I find the dipole works just fine. I don’t miss my 4 element Yagi at 70 feet enough to go through the time, money and work to put up a tower again. Frankly I have worked more QSOs in a contest weekend and more countries in a contest weekend with dipoles than I ever did with the Yagi. Some of that is due to experience and...

All antennas are a compromise. As you only have a given amount of power you can focus all of it in one pinpoint direction at the expense of all other directions or spread it out equally in almost all directions. Gain in one direction is always at the expense of signal strength is other directions. I wrote up some info that may help explain how wire antennas work. The lengths are just ballpark numbers as the exact length depends on many variables such as exact frequency, size of wire, distance above ground, type of insulation and other factors.  Use these lengths as a guide.  Quarter wave wire. Approximate lengths are: 130 feet on 160 meters 65 feet on 80 33 feet on 40 16 feet on 20 10 feet on 15 8 feet on 10  This length wire has zero current at the open end. ( there is always zero current at the open end of a wire) Maximum current at input. Low input impedance. Half wave wire. Approximate lengths: 270 feet on 160 135 feet on 80 67 feet on 40 33 feet on 20 21 fe...