ERP Calculations
This worksheet may be used to calculate your repeater transmit effective
readioted power (ERP). this data must be supplied in order to properly
coordinate your repeater.
Information Needed:
Sponsor: _________________________
Transmit Frequency Band: _________________ MHz
Transmitter Output Power: ____________ Watts (97.103(e)(6))
Antenna Make and Model: __________________________
Antenna Gain (in dB over a half-wave dipole)__________ dBd
Type of Antenna feedline: _________________________
Length of Antenna feed line: _______________ feet
Duplexer Make and Model: ____________________
System Gains:
Transmitter Output Power: ___________________ dBW
Add the Antenna Gain: + __________________ dBd
Equals system gain = __________________ dB
System Losses:
Length of Antenna Feed Line: ___________________ feet
Divide by 100: / 100
Equals: ___________________
Multiply this figure by the
cable loss factor from Table II
X _______________ db per 100 ft.
Equals cable loss in dB ___________________ dB
Add duplexer insertion loss
(if used): + _____________ dB
Equals total system loss = ___________________
Caculate Transmit ERP
System Gain: _________________ dB
Minus System Loss: _________________ dB
Equals ERP in dBW _________________ dBW
Equals ERP in watts: _________________ Watts
Table I
dbW/Watt Table
Watts dBW Watts dBW Watts dBW Watts 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
Table II
50 ohm Coaxial Cable Feed Line Loss Factors (dB pre 100 feet)
------------------------------------------------------------------------
Freq. Cable Type
Band ----------------------------------------------------------
(MHz) RG-58,-223 | RG-8,-213 | RG-9,-214 | 1/2" foam | 7/8" foam
------------------------------------------------------------------------
29 2.8 1.0 1.0 0.4 0.26
52 3.8 1.3 1.4 0.55 0.36
144 7.0 2.6 2.6 1.0 0.66
220 9.0 3.4 3.4 1.3 0.85
440 13.0 5.3 5.1 1.9 1.3
1240 19.0 10.3 10.3 4.2 3.2
------------------------------------------------------------------------
©1998 Iowa Repeater Council, Inc.
All rights reserved.
info@iowarepeater.org
Last modified: Thursday, May 28, 1998