How Can I calculate EIRP?

Hi folks,

What is the maximum EIRP allowed on a point to point wireless link?

I am using Cisco Aironet Bridge 1410, and the Cisco 5.8 GHZ 28dBi dish
antenna

I have set the Air bride to 24dbm/250mw, let me think loud

The EIRP = Tx Output Power (dBW/dBm) + Antenna Gain (dBi) - Line Loss
(dB)

= 24 + 28 + 1.3 (for 20ft cable)
= 53.3 db

Now if want to convert this amount in watts, then I will use this
equation

53.3dB = 10 log (P in mille watts)
5.33db = 10 log P
p = 213796 mw or 213 watts I am sure that I am wrong.

I know that for multi point the maximum EIRP is 4 Watts only

I will appreciate any help

ConceptZone

> What is the maximum EIRP allowed on a point to point wireless link?

Point to Point:

Higher EIRP is allowed if the antennas are directional in nature.

Systems operating in a point-to-point operation may employ transmitting
antennas with directional gain greater than 6 dBi provided the maximum
output power of the transmitter is reduced by 1 dB for every 3 dB that
the directional gain of the antenna that exceeds 6 dBi. Maximum
transmitter power versus largest antenna table for PTP:

Transmitter RF power Antenna Gain EIRP in watts
30dBm 1W 6dBi
3.98
29dBm 800mW 9dBi
6.35
28dBm 630mW 12dBi
10.14
27dBm 500mW 15dBi
15.81
26dBm 398mW 18dBi
25.23
25dBm 316mW 21dBi
40.28
24dBm 250mW 24dBi
62.79
23dBm 200mW 27dBi
100.2

This information is provided as a guideline. If you are not a
professional installer we highly recommend that you read the FCC Part 15
rules and understand them before attempting installations.

From www.fab-corp.com/db.htm

> The EIRP = Tx Output Power (dBW/dBm) + Antenna Gain (dBi) - Line Loss
> (dB)
>
> = 24 + 28 + 1.3 (for 20ft cable)
> = 53.3 db

You've added the line loss not subracted it so should be ~ 50 db give or
take a connector loss.

> p = 213796 mw or 213 watts I am sure that I am wrong.
>
> I know that for multi point the maximum EIRP is 4 Watts only

However, you're still over the US limit but you didn't say which country
you're in.

David.

Currently I am in Saudi Arabia,

Let me recalculate the EIRP

EIRP = 24dbm +28dbi -1.3db = 50.7 db

50.7 dbm = 10 log P
P = 117.48 Watts

Still 117.48 Watts is a tremendous number.

Is this 117.48 Watts a realistic number?


Here is the specification of the dish antenna I am using
http://www.cisco.com/en/US/products/...08022fb7f.html

Also here is the specification of the Aironet Bridge I am using
http://www.cisco.com/en/US/products/...08018495c.html

ConceptZone

On 3 Sep 2005 04:12:06 -0700, "ConceptZone" <(E-Mail Removed)>
wrote:

>What is the maximum EIRP allowed on a point to point wireless link?

In what country? The FCC has be screwing around with the 5.7GHz power
and spectra rules until nobody seems to know what's legal and what's
not. This is a bit old but covers the basics and the politics:
> http://www.cisco.com/en/US/products/...801c4a88.shtml

See:
> http://www.cisco.com/en/US/products/....html#wp998787
in the section starting with "Power Levels". Basically, for point to
point, 1 watt tx maximum into any directional antenna up to 23dBi
gain. After that, a reduction in tx power is required for larger
antennas.

Point-to-point UNII-3 systems can employ the transmitting antennas
with a directional gain up to 23 dBi without any corresponding
reduction in peak transmission power. For antennas with a gain
greater than 23 dBi, a dB reduction in output power is required
for every corresponding dB increase in excess of 23 dBi.

EIRP = Peak transmission power (30 dBm or 1 W) + 23 dBi
= 53 dB (200 W)

>I am using Cisco Aironet Bridge 1410,

Note that Cisco has not obtained regulatory approval for Saudi Arabia,
assuming such approval is required.
> http://www.cisco.com/warp/public/779...provals.html#7


>and the Cisco 5.8 GHZ 28dBi dish
>antenna
>
>I have set the Air bride to 24dbm/250mw, let me think loud
>
>The EIRP = Tx Output Power (dBW/dBm) + Antenna Gain (dBi) - Line Loss
>(dB)
>
> = 24 + 28 + 1.3 (for 20ft cable)
> = 53.3 db

Wrong. You must SUBTRACT your losses and add your gains. EIRP is:
+24dBm + 28dBi -1.3dB = 50.7dBm EIRP
I'm not sure where you got your numbers, but the -1.3dB cable and
connector losses are unrealisticly small. If you describe the RF
components a bit better, we might be able to conjur a more realistic
number.

>Now if want to convert this amount in watts, then I will use this
>equation
>
>53.3dB = 10 log (P in mille watts)
>5.33db = 10 log P
>p = 213796 mw or 213 watts I am sure that I am wrong.

Please memorize:

0dBm = 1 milliwatt
10dBm = 10 milliwatts
20dBm = 100 milliwatts
30dBm = 1 watt
40dBm = 10 watts
50dBm = 100 watts
60dBm = 1000 watts

Yep, it really is about 200 watts EIRP (with the numbers you
supplied). That's one nice thing about microwave frequencies. You
can get literally huge antenna gains, which result in sky high EIRP
levels. However, the much higher free space loss means that there's
no free lunch and that you can't win.

>I know that for multi point the maximum EIRP is 4 Watts only
>
>I will appreciate any help
>
>ConceptZone

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann;16393 Wrote:
> On 3 Sep 2005 04:12:06 -0700,
> That's one nice thing about microwave frequencies. You
> can get literally huge antenna gains, which result in sky high EIRP
> levels. However, the much higher free space loss means that there's
> no free lunch and that you can't win.

Sorry,
"Nice thing about microwave frequences"
you mean compared to higher frequencies right?

"Much higher free space loss"
you mean compared to lower frequencies right?


------------------------------------------------------------------------
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On Sep 19, 10:56 pm, kaon <kaon.2x8...@no-mx.wirelessforums.org>
wrote:
> Jeff Liebermann;16393 Wrote:
>
> > On 3 Sep 2005 04:12:06 -0700,
> > That's one nice thing about microwave frequencies. You
> > can get literally huge antenna gains, which result in sky high EIRP
> > levels. However, the much higher free space loss means that there's
> > no free lunch and that you can't win.
>
> Sorry,
> "Nice thing about microwave frequences"
> you mean compared to higher frequencies right?

The higher the frequency, the smaller the antenna.
Translation - a 5 dB gain 42 MHz Yagi will get torn off the headache
rack on my pickup when driving through a Burger King, but a 5.8 GHz
antenna is smaller than a Barbie Doll accessory.

> "Much higher free space loss"
> you mean compared to lower frequencies right?

There really isn't greater attenuation, rather the antenna is "less
sensitive" at higher frequencies.

I'll start a new thread about that.

kaon <(E-Mail Removed)> hath wroth:

>Jeff Liebermann;16393 Wrote:
>> On 3 Sep 2005 04:12:06 -0700,
>> That's one nice thing about microwave frequencies. You
>> can get literally huge antenna gains, which result in sky high EIRP
>> levels. However, the much higher free space loss means that there's
>> no free lunch and that you can't win.

>"Nice thing about microwave frequences"
>you mean compared to higher frequencies right?

Yep. For a given antenna aperature size, the gain increases with
frequency. For example, the gain of a parabolic dish is:
dBi = 20 * Log(N * Pi)
where N = diameter in wavelengths.
You can see that as the frequency increases, the number of wavelengths
in the dish diameter also increases, thus increasing the gain. Double
the number of wavelengths in the diameter, and the dish gain increases
by 6dB.

>"Much higher free space loss"
>you mean compared to lower frequencies right?

Correct. As the frequency goes up, so does the free space losses.
<http://www.terabeam.com/support/calculations/free-space-loss.php>
Double the frequency, and the free space loss goes up 6dB, which
cancels the the 6dB gain increase in the antenna gain.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sep 21, 12:47 am, Jeff Liebermann <je...@cruzio.com> wrote:
> kaon <kaon.2x8...@no-mx.wirelessforums.org> hath wroth:

> >"Much higher free space loss"
> >you mean compared to lower frequencies right?
>
> Correct. As the frequency goes up, so does the free space losses.
> <http://www.terabeam.com/support/calculations/free-space-loss.php>
> Double the frequency, and the free space loss goes up 6dB, which
> cancels the the 6dB gain increase in the antenna gain.

Not so.

The total path loss does indeed increase (as shown by on-line
calculator above), but not due to free space loss; rather less signal
is captured by the antenna.

(E-Mail Removed) hath wroth:

>On Sep 21, 12:47 am, Jeff Liebermann <je...@cruzio.com> wrote:
>> kaon <kaon.2x8...@no-mx.wirelessforums.org> hath wroth:
>
>> >"Much higher free space loss"
>> >you mean compared to lower frequencies right?
>>
>> Correct. As the frequency goes up, so does the free space losses.
>> <http://www.terabeam.com/support/calculations/free-space-loss.php>
>> Double the frequency, and the free space loss goes up 6dB, which
>> cancels the the 6dB gain increase in the antenna gain.

>Not so.
>
>The total path loss does indeed increase (as shown by on-line
>calculator above), but not due to free space loss; rather less signal
>is captured by the antenna.

Try again. The free space loss calculation does not in any way
involve the antenna. It is the loss between two isotropic antennas at
a given frequency and a given distance only. If there were anything
involving the antenna (capture area, aperature size, gain, beamwidth,
etc), then it would appear in the free space loss formulas and
calculations. They don't. There's no antenna gain in any of the
formulas on this page:
<http://en.wikipedia.org/wiki/Free-space_loss>

What do you mean by "total path loss"? Are you including the
transmitter, antennas, receiver, coax cables, and propagation
imparements? If so, you're talking about system gain/loss, which is a
different animal, and certainly includes the antenna gains. If you
want to measure your path loss between the antenna ports, that's fine,
but it's NOT the free space loss.

Quiz: You have a broadband dish antenna at both ends of a fixed
2.4GHz link. Shove 0dBm into one antenna and you get -60dBm at the
other end of the link. Now, double the frequency to 4.8GHz. What's
the signal level at the other end?

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sep 21, 1:47 am, Jeff Liebermann <je...@cruzio.com> wrote:
> nevtxjus...@gmail.com hath wroth:
>
> >On Sep 21, 12:47 am, Jeff Liebermann <je...@cruzio.com> wrote:
> >> kaon <kaon.2x8...@no-mx.wirelessforums.org> hath wroth:
>
> >> >"Much higher free space loss"
> >> >you mean compared to lower frequencies right?
>
> >> Correct. As the frequency goes up, so does the free space losses.
> >> <http://www.terabeam.com/support/calculations/free-space-loss.php>
> >> Double the frequency, and the free space loss goes up 6dB, which
> >> cancels the the 6dB gain increase in the antenna gain.
> >Not so.
>
> >The total path loss does indeed increase (as shown by on-line
> >calculator above), but not due to free space loss; rather less signal
> >is captured by the antenna.
>
> Try again.

I'll rephrase it this way.... The effective free space loss does
indeed increase (as shown by the on-line calculator above), but not
due to attenuation traveling through free space; rather less signal is
captured by the antenna.

>The free space loss calculation does not in any way
> involve the antenna. It is the loss between two isotropic antennas at
> a given frequency and a given distance only. If there were anything
> involving the antenna (capture area, aperature size, gain, beamwidth,
> etc), then it would appear in the free space loss formulas and
> calculations. They don't. There's no antenna gain in any of the
> formulas on this page:
> <http://en.wikipedia.org/wiki/Free-space_loss>

Ok, slow down...I don't think were on the same page yet.

Its not obvious in the formula for the on-line calculator, but if you
examine how that formula was derived, you can see how antenna capture
area was used.

On http://en.wikipedia.org/wiki/Free-space_loss, read down to the
Physical explanation section and you'll see "The second effect is that
of the receiving antenna's aperture, which describes how well an
antenna can pick up power from an incoming electromagnetic wave...Note
that this is entirely dependent on wavelength, which is how the
frequency-dependent behaviour arises."


> What do you mean by "total path loss"? .... .... If you
> want to measure your path loss between the antenna ports, that's fine,
> but it's NOT the free space loss.

See above. Since just about all of my equipment is similar, I don't
need to input any variables such as different antennas, I'm just so
used to saying "total path loss" to describe the free space
attenuation. Sorry for the confusion.


> Quiz: You have a broadband dish antenna at both ends of a fixed
> 2.4GHz link. Shove 0dBm into one antenna and you get -60dBm at the
> other end of the link. Now, double the frequency to 4.8GHz. What's
> the signal level at the other end?

Unwittingly, that could be a trick question.

If you had a unity gain quarter-wave antennas at the receiving end and
doubled the frequency,
the answer is -66 dBm as the 4.8 GHz antenna has one fourth the
capture area.

If you had increased the gain of the receiving antenna by making it
four times longer (as in a four element co-linear array), you increase
the capture area by four times, so the answer would be -60 dBm.

Since you didn't specify that you used a smaller antenna when you
doubled the frequency, rather retained the same square area and thus
increased the gain by four times, the answer is -60 dBm.