Some of the antenna stuff you hear on the air these days makes you think that 2 plus 2 now equals 5. A few basic facts about radio waves and antennas are therefore needed. If you look around at the radio waves passing by, you will see some strong ones, some weak ones, and some in between. The way you measure a radio wave is in volts, just like a battery, except RF volts. Since the radio wave doesn’t have terminals on the end, we pick some spots on the wave to measure the voltage. The normal measurement is between two points on the wave on meter, about 39 inches, apart. The voltage is not much, so we usually measure millivolts or event microvolts. We have to measure the wave in the plane of polarization, if it’s vertical we measure the vertical meter distance, and if it’s horizontal we measure horizontal. The result is that we get a measurement of so many microvolts or millivolts per meter. For example, if you measured a broadcast signal from a 1000 watt station at one mile, you should get about 150 mV/meter. A TV station at 30 miles should measure about 3 mv/meter. Most ham band signals will measure between 1 and 100 uv/meter, if you are a few miles away.
Now how much signal does your antenna get from that radio wave? It depends upon how long it is. If the signal is 50 uv/meter and your antenna is 10 meters long, in the plane of polarization of the wave, you will get 50 x 10 = 500 microvolts into your receiver. If your antenna is 50 meters long, you will get 2500 uv. So, the longer the antenna, or the stronger the radio wave, the louder the signal. So also, small antennas = small signals and big antennas = big signals, no way around it, so hang up some wire.
Chuck Teeters
W4MEW