Radio waves can bounce off objects and solid surfaces. Travel at 186,000 miles per second. 299,000 kilometres per second. Frequency is the number of waves that travel past in a second; unrelated to the speed. This is the length of the waves. Amplitude is the measure of the height of the wave. Phase is the relationship between two signals. If the signals are out of phase; the two signals have the waves reversed in relation to each other. Frequency Modulation; this modifies the frequency to send data. Phase modulation; modifying the phase to send data. Phase shift keying; PSK signal starts and stops to send a binary data signal.
- 1mw = odbm.
- 2mw = +3dbm.
- 4mw = +6dbm.
- 10mw = +10dbm.
- 20mw = +13dbm.
- 14mw = +25dbm.
- 1000mw = +30dbm.
- 10,000mw = +40dbm.
- +/- 100,000mw – 50 dbm.
- -3dbm half the wattage value.
- +3dbm Double the wattage value.
- -10dbm – Decrease watt value to one-tenth of the original.
- +10dbm – Increase the watt value by ten times.
A decrease of 3 dBm gives us about half of the original value. Increasing by 3 dBm gives us about double the original value.
Signal to noise ratio: this gives us the ratio of noise to signal.
Signal scattering can cause the signal to be scattered.
Attenuation; this is loss of signal strength over distance.
Gain; the positive difference in amplitude between two signals.
Free space path loss is the natural loss of signal in space.
Waves decrease in power over distance
Waves bounce off things.
Waves are absorbed by things.
Lower frequency waves are bigger.
Bigger waves penetrate better.
Choices for open license communications: 900mhz, 2.4 GHz, 3.5ghz 5ghz.
How to make a radio transmitter work optimally.
-Good placement.
-Select the right frequency.
-Right hardware.
Point to point wireless link: rain fade. Absorption. Using a 900 megahertz link would be better than 5ghz. Proper antenna with a focused beam.