Advanced Amateur Radio Exam
Section A-007-006 Effective Radiated Power
Section A-007-006 Effective Radiated Power
Effective Radiated Power (ERP) is a crucial concept in radio communications, indicating the actual power transmitted from an antenna. It takes into account the transmitter's output power, any losses in the transmission line and connectors, and the gain provided by the antenna. Understanding how to calculate ERP is essential for optimizing transmission systems and adhering to regulatory requirements.
Effective Radiated Power means the transmitter's output power minus any line losses, plus the antenna's gain relative to a dipole. Increasing the overall gain of an amateur station by 3 dB effectively doubles the ERP. This is because every 3 dB increase in gain represents a doubling of power. A 1 dB loss is equivalent to about 20%.
For a transmitter with an output of 100 watts experiencing a 3 dB loss in the cable and connectors and using an antenna with a 6 dBd gain, the ERP calculation goes as follows:
A 3 dB loss halves the power:
100 watts/2=50 watts
A 6 dBd gain doubles the power twice:
50 watts×2×2=200 watts
Thus, the ERP is 200 watts.
As the standing wave ratio (SWR) increases, losses in the transmission line due to dielectric and conductor heat also rise, affecting the ERP. These losses can be significant, especially in poorly tuned systems.
If a transmitter outputs 200 watts, with a transmission line loss of 5 watts and an antenna gain of 3 dBd, the ERP is calculated as follows:
Subtracting the line loss:
200 watts−5 watts=195 watts
A 3 dBd gain is equivalent to doubling the power:
195 watts×2=390 watts
Hence, the ERP in this scenario is 390 watts.
For a transmitter with a 200-watt output, experiencing a 3 dB total loss in coaxial and connectors, and using an antenna with a 9 dBd gain, the ERP is calculated as:
A 3 dB loss halves the power:
200 watts/2=100 watts
A 9 dBd gain is equivalent to doubling the power thrice:
100 watts×2×2×2=800 watts
Thus, the ERP is approximately 800 watts.
For a 100-watt transmitter with a 1.30 dB loss in the transmission line and 0.2 dB loss through the antenna tuner, combined with a 4.50 dBd gain in the antenna, the ERP calculation involves:
A total loss of 1.50 dB (1.30 dB + 0.2 dB), which slightly less than halves the power.
A 4.50 dBd gain, which more than doubles the power.
Approximately, this results in an ERP of 200 watts.
In a system where a transmitter has a power output of 125 watts, experiencing 0.8 dB loss in the transmission line and 0.2 dB in the antenna tuner, combined with a 10 dBd gain in the antenna, the ERP is calculated as:
The losses slightly reduce the power, while the 10 dBd gain (equivalent to tenfold increase) significantly raises it.
The final ERP in this case is approximately 1000 watts.
Replacing a 3 dBd gain antenna with a 9 dBd gain antenna, with no other changes, increases the ERP by a factor of 4. This is because the antenna's gain contributes significantly to the overall ERP.
For a transmitter with 2000 watts PEP and 1 dB composite loss in the transmission line, connectors, and antenna tuner, combined with a 10 dBd gain from a stacked Yagi antenna, the ERP is calculated as:
A 1 dB loss slightly reduces the 2000 watts PEP, but the 10 dBd gain significantly increases it, resulting in an ERP of approximately 16,000 watts PEP.
Similarly, a transmitter with 1000 watts PEP and the same loss and gain parameters would have an ERP of around 8000 watts PEP.
Accurately calculating the Effective Radiated Power is essential for designing efficient radio transmission systems and ensuring regulatory compliance. By understanding the interplay of transmitter power, line losses, and antenna gain, one can optimize the performance of radio communication systems, ensuring effective and reliable transmission.