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EIRP and ERP

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Joe G \(Home\)

Jan 1, 1970
0
HI All,

What the difference between EIRP (Effective Isotropic Radiated Power) and
ERP (Effective Radiated Power)?

Are both EIRP and ERP feild measurements?

How do you relate EIRP / ERP to dBuV/m?


Why the questions - the reguilations on some Tx requipment state an EIRP
limits / requirements

BUT EIRP is what's coming out the antenna.

So if you measure 5watts at the 50ohm termination - you have to factor in
cable loss and Antenna gain loss.

So I guess EIRP = Power (50ohm) - cable loss + Antenna gain + (EIRP / ERP
factor) .... correct?


Thanks in advance

Joe
 
F

Fred Abse

Jan 1, 1970
0
HI All,

What the difference between EIRP (Effective Isotropic Radiated Power) and
ERP (Effective Radiated Power)?

Effective radiated power is the power supplied to an antenna multiplied by
the gain of that antenna compared to some standard antenna. Unqualified,
it is usually taken to refer to the gain over a half wave dipole, but it
doesn't have to be, it should really be stated.

Effective isotropic radiated power is just effective radiated power
referred to a theoretical isotropic radiator, which radiates equally in
all directions. Such a device does not physically exist, but is
nevertheless useful in theoretical field calculations.

Effective radiated power is usually taken to mean ERP in the direction of
maximum radiation for the antenna under consideration.

A dipole antenna which is electrically one half wave long, in free space,
exhibits a gain in its direction of maximum radiation of 2.15dB over a
theoretical isotropic radiator.
Are both EIRP and ERP feild measurements?

Somebody at some time will have made field measurements to derive the
antenna's polar pattern, hence its gain, but ERP is usually just derived
from input power and antenna manufacturers' gain figures.

How do you relate EIRP / ERP to dBuV/m?

From antenna gain, radiated power and the inverse square law, hence power
density (watts per square meter), and the intrinsic impedance of free
space (120 * pi, about 277 ohms))
Why the questions - the reguilations on some Tx requipment state an
EIRP limits / requirements

BUT EIRP is what's coming out the antenna.

So if you measure 5watts at the 50ohm termination - you have to factor
in cable loss and Antenna gain loss.
Correct


So I guess EIRP = Power (50ohm) - cable loss + Antenna gain + (EIRP /
ERP factor) .... correct?

No, EIRP = (power to feeder) *times* feeder loss *times* (antenna gain
over isotropic).
 

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