Engineering Notes

POWER RF AMPLIFIERS TECHNICAL REFERENCE MATERIAL

% Modulation = (( PEP - P_C) / P_C) *100%

Example:
Carrier Power P_C = 100 W, PEP = 400 W.
Determine % Modulation

M% = ((400 - 100) / 100) *100% = ((20-10) / 10) *100% = 100%

MOD. DEPTH	AVERAGE POWER INCREASE DUE TO MODULATION		RATIO OF PEP TO CARRIER POWER
M%	dB = 10 LOG (1 + M2 / 2)	RATIO	dB = LOG (1 + M)2	RATIO
30 50 70 80 85 90 95 100	0.19 0.51 0.95 1.21 1.34 1-48 1.62 1.76	1.05 1.13 1.25 1.32 1.36 1.41 1.45 1.50	2.3 3.5 4.6 5.1 5.3 5.6 5.8 6.0	1.7 2.3 2.9 3.2 3.4 3.6 3.8 4.0

M U L T I P L E  C A R R I E R S

Phasor Representation

Voltage Maximum Example: F1 = 10 MHz F2 = 10.1 MHz E1 = E2 = IV RL = 1 Ohm

S I N G L E  C A R R I E R  C A S E  ( F₁ o n l y )

P = E² / R = (1)² / 1 = 1 Watt CW or PEP

T W O  C A R R I E R  C A S E  ( F₁ & F₂ )

The voltage phasors, E₁ & E₂ are at a maximum every 10 microseconds since:
Coincidence Rate = 1 / (F₂ - F₁) = 1 / ((10.1 - 10) *10⁶) = 10 Microseconds

At coincidence E₁ & E₂ add directly, therefore:
P = E₂ / R = (1+1)₂ / 1 = 4 Watts PEP

N  C A R R I E R  C A S E  (F₁ + F₂ ... +F_n)

P = E₂ / R = N₂ / 1 = N₂ Watts PEP

NUMBERS OF CARRIERS	POWER IN EACH CARRIER FOR 7 W PEP OUTPUT	PEP OUTPUT POWER FOR N 1 W CARRIERS
N	P = 1 / N2 Watts	P = N2 Watts
1 2 3 4 10	1 W 250 mW 111 mW 63 mW 10 mW	1 W 4 W 9 W 16 W 100 W

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