通信基础知识（Basic knowledge of communication）.docVIP

通信基础知识（Basic knowledge of communication） A and RF knowledge Power / level (dBm): output power of amplifier, general units are w, MW, dBm Note: dBm is the absolute power level expressed in decibels, taking 1MW as the reference value. Conversion formula: Level (dBm) =10lg 5W to 10lg5000=37dBm 10W to 10lg10000=40dBm 20W to 10lg20000=43dBm It is not difficult to see that the power level increases by 3dBm each time the power is doubled Gain (dB): that is, the amplification factor can be expressed in decibels (dB). Namely: dB=10lgA (A is power amplification) Insertion loss: the attenuation of a device or component into a transmission circuit. The unit is represented by dB. Selectivity: measures the gain in the operating band and the ability to suppress radiation outside the band. -3dB bandwidth, that is, when the gain goes down by 3dB, the bandwidth is the same as that of -40dB and -60dB. In Bobbi (return loss): for the standing wave state, and the node voltage of voltage loop ratio (VSWR) Attached: stationed in Bobbi - echo loss comparison table: SWR, 1.2, 1.25, 1.30, 1.35, 1.40, 1.50 Return loss (dB) 211917.6, 16.6, 15.6, 14 Three order intermodulation: if there are two sinusoidal signals, Omega 1 and Omega 2, because of the nonlinear effects, many intermodulation components will be generated, of which 2, Omega, 1-, Omega 2 and 2 Omega 2-, Omega 1, and two frequency components are called Three order intermodulation component, whose power P3 and signal Omega 1 or omega 2 power ratio is called three order cross modulation factor M3. That is, M3, =10lg, P3/P1 (dBc) Noise factor: generally defined as the ratio of the output signal-to-noise ratio to the input signal-to-noise ratio, which is actually converted to decibels in actual use. Unit with dB. Coupling degree: the power ratio between the coupling port and the input port, and the unit is dB. Isolation: the ratio of the power of this oscillator or signal to other ports to the original power, dB. Antenna gain (dB): the ab