EIRP

Hi
can anybody explain me what is the physical sense of EIRP.
I mean I know the equations and how to count it but i can't understand about
what this magnitude inform me.

thx
michal

mikez <(E-Mail Removed)> wrote:
> Hi
> can anybody explain me what is the physical sense of EIRP.
> I mean I know the equations and how to count it but i can't understand about
> what this magnitude inform me.

Effective Isotropic Radiated Power.
For example, a laser pointer has a power of 5mw or so.
The beam has an angle of around 0.5 milliradians. (1/30th of a degree).
To have a 360 degree floodlight with the same visible brightness would
need around 50000W.

In article <bngm94$lov$3$(E-Mail Removed)>,
Ian Stirling <(E-Mail Removed)> wrote:
> mikez <(E-Mail Removed)> wrote:
> > can anybody explain me what is the physical sense of EIRP.
> > I mean I know the equations and how to count it but i can't understand about
> > what this magnitude inform me.
>
> Effective Isotropic Radiated Power.
> For example, a laser pointer has a power of 5mw or so.
> The beam has an angle of around 0.5 milliradians. (1/30th of a degree).
> To have a 360 degree floodlight with the same visible brightness would
> need around 50000W.

So it's something like watts per steradian?

--
-eben (E-Mail Removed)m home.tampabay.rr.com/hactar

And we never failed to fail / It was the easiest thing to do -- CSN

Hactar <(E-Mail Removed)> wrote:
> In article <bngm94$lov$3$(E-Mail Removed)>,
> Ian Stirling <(E-Mail Removed)> wrote:
>> mikez <(E-Mail Removed)> wrote:
>> > can anybody explain me what is the physical sense of EIRP.
>> > I mean I know the equations and how to count it but i can't understand about
>> > what this magnitude inform me.
>>
>> Effective Isotropic Radiated Power.
>> For example, a laser pointer has a power of 5mw or so.
>> The beam has an angle of around 0.5 milliradians. (1/30th of a degree).
>> To have a 360 degree floodlight with the same visible brightness would
>> need around 50000W.
>
> So it's something like watts per steradian?

Not directly.
Isotropic = same in all directions.
So, EIRP is a way to rate the emission of antenna by comparing it
to a one that radiates equally in all directions. (somewhat rare for
RF)

If you need a EIRP of 1W to be recieved at some distance, you can
either use a antenna with a beam of around 60 degrees (1 radian) and
1/12th of a watt, a 6 degree beam with 1/1200th of a watt, ...

In article <bnh8j5$652$1$(E-Mail Removed)>,
Ian Stirling <(E-Mail Removed)> wrote:
> Hactar <(E-Mail Removed)> wrote:
> > In article <bngm94$lov$3$(E-Mail Removed)>,
> > Ian Stirling <(E-Mail Removed)> wrote:
> >> mikez <(E-Mail Removed)> wrote:
> >> > can anybody explain me what is the physical sense of EIRP.
> >> > I mean I know the equations and how to count it but i can't understand about
> >> > what this magnitude inform me.
> >>
> >> Effective Isotropic Radiated Power.
> >> For example, a laser pointer has a power of 5mw or so.
> >> The beam has an angle of around 0.5 milliradians. (1/30th of a degree).
> >> To have a 360 degree floodlight with the same visible brightness would
> >> need around 50000W.
> >
> > So it's something like watts per steradian?
>
> Not directly.
> Isotropic = same in all directions.
> So, EIRP is a way to rate the emission of antenna by comparing it
> to a one that radiates equally in all directions. (somewhat rare for
> RF)

Gotcha. BTW, do you know how many steradians are in a sphere?

> If you need a EIRP of 1W to be recieved at some distance, you can
> either use a antenna with a beam of around 60 degrees (1 radian) and
> 1/12th of a watt, a 6 degree beam with 1/1200th of a watt, ...


Ah, so EIRP applies to receiving antennas as well as transmitting ones?

Where can I find more information about EIRP (specifically, the EIRPs of
typical antennas)?

--
-eben (E-Mail Removed)m home.tampabay.rr.com/hactar

Logic is a systematic method of coming to
the wrong conclusion with confidence.

"Hactar" <(E-Mail Removed)> wrote in message
news:bnhag2$kj5$(E-Mail Removed)...
> In article <bnh8j5$652$1$(E-Mail Removed)>,
> Ian Stirling <(E-Mail Removed)> wrote:
<snip...>
> > Isotropic = same in all directions.
> > So, EIRP is a way to rate the emission of antenna by comparing it
> > to a one that radiates equally in all directions. (somewhat rare for
> > RF)
>
> Gotcha. BTW, do you know how many steradians are in a sphere?

Defined by analogy to radians in the plane. A radian is the angle subtended
by an arc of length r on a unit circle, where r is radius. So, there are
2*pi radians in a circle. A steradian is the solid angle subtended by a
patch of area r^2 on a unit sphere, so there are 4*pi steradians in a
sphere.

>
> > If you need a EIRP of 1W to be recieved at some distance, you can
> > either use a antenna with a beam of around 60 degrees (1 radian) and
> > 1/12th of a watt, a 6 degree beam with 1/1200th of a watt, ...
>
>
> Ah, so EIRP applies to receiving antennas as well as transmitting ones?

No, this refers to the transmitting antenna. Think of like this. An
isotropic antenna radiates equal power in all directions, so if you took a 1
meter square frame to a distance of 10 meters *in any direction* from an
isotropic antenna, you'd measure the same amount of energy flowing through
that frame every second (that is, the same power). If you took the same
frame out 20 meters *in any direction*, the measured power would would be
four times smaller than the measurement at 10 meters, but it would the same
at any position 20 meters out.

Anisotropic antennas radiate power asymmetrically - in some directions, they
radiate more power, in other directions less. It's easiest to think of a
directional antenna that tries to focus power in a beam. Over the angle
subtended by the antenna dish, there is transmitted power, outside that
radiating cone the power drops off to zero. If the total power is P, it
should be pretty clear that an isotropic antenna would spread P out over a
whole 4 steradians, while all of the power P is concentrated in the cone of
the directional antenna. So the 1meter square window will measure a higher
radiated power at 10 meters in the directional antenna's cone than at 10
meters from the isotropic antenna. The ratio of the two powers is the
directional antenna's gain - just a measure of how well the directional
antenna concentrates power compared to the isotropic antenna. That why gain
is measured in dBi - "decibels compared to istropic".

EIRP just encapsulates the fact that the receiver can't tell if the power
came from an isotropic or a directed antenna. It can't tell if the received
power came from an isotropic antenna transmitting with power P or a
directional antenna transmitting at power P/100 with a gain of 100. So, the
directional antenna transmitting P/100 with a gain of 100 has EIRP of P - it
looks to a distant receiver like an isotropic antenna radiating at power P,
even though it really only radiates P/100.

>
> Where can I find more information about EIRP (specifically, the EIRPs of
> typical antennas)?

Just run a Google or Yahoo search on EIRP, and you find more hits than you
can handle.

>
> --
> -eben (E-Mail Removed)m home.tampabay.rr.com/hactar
>
> Logic is a systematic method of coming to
> the wrong conclusion with confidence.

Entity gary spoke thus:

> If you took the same
> frame out 20 meters *in any direction*, the measured power would would be
> four times smaller than the measurement at 10 meters
OK, but what is the formula for that? I know it's the same as gravity,
inverse square or some such thing.

--Gnarlie

In article <(E-Mail Removed) m>,
Gnarlodious <(E-Mail Removed)> wrote:
> Entity gary spoke thus:
>
> > If you took the same
> > frame out 20 meters *in any direction*, the measured power would would be
> > four times smaller than the measurement at 10 meters
> OK, but what is the formula for that? I know it's the same as gravity,
> inverse square or some such thing.

Somebody who knows this junk stop me when I go astray.

Take the input power. If it goes to an isotropic antenna, it's spread
evenly over 4*pi steradians.

Actually, I'd better stop there. I don't know what data is given and
what results there should be.

--
-eben (E-Mail Removed)m home.tampabay.rr.com/hactar

They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety. -- Ben Franklin

So, for some real antenna that radiates power P, the EIRP rating is the
power that would be radiated by an isotropic antenna to produce the same
power at some distant receiver.

For a point at distance d, the power flux density is

PFD(d) = EIRP/(4*pi*d^2)

because the isotropic antenna radiates symmetrically in all directions
(there's your inverse square).

So the power transmitted through a patch of area A (actually a patch on the
surface of an imaginary sphere) at a distance d is

P(A,d) = A*PFD(d) = A*EIRP/(4*pi*d^2)

"Gnarlodious" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) s.com...
> Entity gary spoke thus:
>
> > If you took the same
> > frame out 20 meters *in any direction*, the measured power would would
be
> > four times smaller than the measurement at 10 meters
> OK, but what is the formula for that? I know it's the same as gravity,
> inverse square or some such thing.
>
> --Gnarlie
>

Entity gary spoke thus:

> For a point at distance d, the power flux density is
>
> PFD(d) = EIRP/(4*pi*d^2)
OK, so is it safe to simplify by saying that the field strength decreases
linearly with the inverse square of the distance?

-- Gnarlie
http://www.Spectrumology.com
Spectrumology is the science of chaos.