Repeater Transmitter ERP and Feedline Loss Computations

Use this worksheet to compute the repeater's transmitter effective radiated power by starting with the transmitter output power and reducing it due to the loss of the duplexer and antenna feedline and increasing it due to antenna gain. This worksheet is not a calculator. It merely shows the method use to compute the transmitter ERP.

CALCULATING ERP
(use Table I to convert between 
Watts and dBW)
Transmitter output  watts   dBW
Minus duplexer insertion loss  -  dB
Duplexer output     watts   dBW
Minus feedline loss            -  dB
Antenna input       watts   dBW
Plus antenna gain              +  dB
Effective radiated power (ERP) =  dBW
Effective radiated power (ERP) =  watts
 
TABLE I
 W  dBW   W  dBW    W  dBW     W  dBW
 1  0.0  15 11.8  100 20.0   800 29.0
 2  3.0  20 13.0  150 21.8   900 29.5
 3  4.8  25 14.0  200 23.0  1000 30.0
 4  6.0  30 14.8  250 24.0  1500 31.8
 5  7.0  40 16.0  300 24.8  2000 33.0
 6  7.8  50 17.0  350 25.4  2500 34.0
 7  8.5  60 17.8  400 26.0  3000 34.8
 8  9.0  70 18.5  500 27.0  4000 36.0
 9  9.5  80 19.0  600 27.8  5000 37.0
10 10.0  90 19.5  700 28.5  6000 37.8
CALCULATING FEEDLINE LOSS
Length of feedline  feet
Divide by 100     =
Multiply by cable loss from
Table II          x dB per 100 feet
                  = loss of feed (dB)
 
TABLE II
50 ohm Coaxial Cable Loss
(dB per 100 feet)
Freq              Cable Type           
Band  RG-58 RG-8  RG-9, RG-8U 1/2"  7/8"
(Mhz) -223  -213  -214  9913  Foam  Foam
 
  29   2.8   1.0   1.0  0.7   0.4   0.3
  52   3.8   1.3   1.4  0.9   0.6   0.4
 144   7.0   2.6   2.6  1.5   1.0   0.7
 222   9.0   3.4   3.4  1.9   1.3   0.9
 440  13.0   5.3   5.3  2.9   1.9   1.3
 902  17.5   7.6   7.6  4.2   3.1   2.5
1240  19.0  10.3  10.3  5.1   4.2   3.2