Microwave Radio System Gain

MICROWAVE RADIO SYSTEMS GAIN

System Gain * Gs is the difference between the nominal output power of a transmitter (Pt) and the minimum input power to a receiver (Cmin) necessary to achieve satisfactory performance; * Must be greater than or equal to the sum of all gains and losses incurred by a signal as it propagates from a transmitter to a receiver * In essence, system gain represents the net loss of a radio system, which is used to predict the reliability of a system for a given set of system parameters.

* Ironically, system gain is actually a loss. * Losses are much higher than the gains. * Therefore, the net system gain always equates to a negative dB value (i.e., a loss) * Because system gain is defined as a net loss * individual losses are represented with positive dB * individual gains are represented with negative dB * Mathematically, system gain in its simplest form is * Gs = Pt - Cmin

where
Gs = system gain (dB)
Pt = transmitter output power (dBm or dBW)
Cmin = minimum receiver input power necessary to achieve a given reliability and quality objective

* Gs = Pt - Cmin > = losses – gains * Pt - Cmin >= FM(dB) + Lp(dB) + Lf(dB) + Lb(dB)- At(dB)- Ar(dB)
Gains:
* At= transmit antenna gain relative to an isotropic radiator (dB) * Ar = receive antenna gain relative to an isotropic radiator (dB)
Losses
* FM = fade margin for a given reliability objective (dB) * Lp = free-space path loss in (dB) * Lf= transmission line loss in (dB) * Lf= total coupling or branching loss in (dB) *
FADE MARGINS
(Link Margin)
Fading
* The reduction in receive signal level; * Reduction in signal strength at the input to a receiver; * It applies to propagation variables in the physical radio path that affect changes in the path loss between transmit and receive antennas

What Is Fade Margin? * Considers the non-ideal and