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Engineering Notes


RF POWER AMPLIFIERS TECHNICAL REFERENCE MATERIAL


Peak Envelope Power


PEP (AM)

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

Example:

Carrier Power PC = 100 W, PEP = 400 W.

Determine % Modulation

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

rf amplifiers peak envelop power
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
MULTIPLE & CARRIERS
Phasor Representation

Voltage Maximum

Example:

F1 = 10 MHz
F2 = 10.1 MHz
E1 = E2 = IV
RL = 1 Ohm

SINGLE CARRIER CASE (F1 only)

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

TWO CARRIER CASE ( 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 CARRIER CASE (F1 + F2 ... +Fn)

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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