dB, Watts, ERP, EIRP calculations

Terrestrial Communication

OFCOM are proposing to implement ICNIRP 1998/2020 recommendations regarding a safe separation distance for the general public exposure to EMF in the range 100kHz to 300GHz.

In 2020 ICNIRP say that overall evaluation of all the research on RF EMFs leads to the conclusion that RF EMF exposure below the thermal threshold is unlikely to be associated with adverse health effects.

Radio Amateurs using yagi beam antennas need to consider the Fresnel zone, the region of space between and around a transmitter and a distant receiver. Remember with a yagi antenna it is the area within the bounds of the main forward lobe where maximum exposure could potentially occur. It is important therefore to know the likely EIRP on the chosen beam heading!

Entering the calculated EIRP into OFCOM's emf-calculator it is then possible to establish the safe separation distance, and if this can be achieved at a particular station location?

Duty cycle and length of time of exposure also need to be considered to mitigate. As an example consider a transmitter with a maximum EIRP of 8KW, a duty factor of 50%, and a maximum percentage of time transmitting of 50%, then we can calculate an average power of 2KW (8,000 Watts x 50% x 50% = 2,000 Watts).
So, using OFCOM's emf-calculator the safe separation distance at 144MHz would be 14.27 metres.

Space Communication

Beam antennas used for Space Communication will be pointed skyward, for EME operation a typical elevation angle of 30° will reduce/minimise general public exposure to EMF.

Suitable Test Equipment

SMP2 is currently the only Meter that will measure both E & H fields in one unit, seen here with WPF3 (100kHz - 3GHz) head!

SMP2 is currently the only Meter that will measure both E & H fields in one unit, seen here with WPF3 (100kHz - 3GHz) head! It is available from APC formerly Aspen Electronics


Convert Watts to dBW

Enter Watts: dBW =  

Convert dBW to Watts

Enter dbW: Watts =  

Calculate ERP and EIRP

Enter Power at Antenna Terminals:
Enter Antenna Gain:
 
Effective Radiated Power (ERP): dBW = Watts =
Effective Isotropic Radiated Power (EIRP): dBW = Watts =

Working example antenna system 2 x CQM12UX at 20M above ground seen in 4nec2

Working example antenna system 2 x CQM12UX at 20M above ground

Two 144MHz yagis design ID CQM12UX stacked one above the other at 20M above ground produces around 22.4dBi forward gain at 4° elevation due to enhancement from ground gain. Confirmed below in K6STI's AOP (AO Professional version software), note there is a very small difference in AOP V's 4nec2 results...

Two 144MHz yagis design ID CQM12UX stacked one above the other at 20M above ground produces a staggering 22.4dBi forward gain at 4° elevation due to enhancement from ground gain! Confirmed in K6STI's AOP (AO Professional version software)

Assume 400 Watts at antenna terminals!

In this particular case with a maximum EIRP of 69.512KW, a duty factor of 50%, and a maximum percentage of time transmitting of 50%, then we can calculate an average power of 17.378KW (69,512 Watts x 50% x 50% = 17,378 Watts). So, using OFCOM's emf-calculator the safe separation distance at 144MHz would be 42.07 metres.

| 2CQM12UX.ANT | 2CQM12UX.nec |


Working example antenna system single CQM10DX at 7M above ground seen in 4nec2

Working example antenna system single CQM10DX at 7M above ground

Single 144MHz yagi design ID CQM10DX located at 7M above ground produces some 20dBi forward gain at 4° elevation due to enhancement from ground gain. Confirmed below in K6STI's AOP (AO Professional version software), note there is a very small difference in AOP V's 4nec2 results...

Single 144MHz yagi design ID CQM10DX at 7M above ground produces a staggering 20dBi forward gain at 4° elevation due to enhancement from ground gain! Confirmed in K6STI's AOP (AO Professional version software)

Assume 400 Watts at antenna terminals!

In this particular case with a maximum EIRP of 39.269KW, a duty factor of 50%, and a maximum percentage of time transmitting of 50%, then we can calculate an average power of 9.817KW (39,269 Watts x 50% x 50% = 9,817 Watts). So, using OFCOM's emf-calculator the safe separation distance at 144MHz would be 31.62 metres.

| GCQM10DX.ANT | GCQM10DX.nec |


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