# How Can I calculate EIRP?

G

#### Guest

##### Guest

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

G

#### Guest

##### Guest

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/hw/wireless/ps469/products_data_sheet09186a008022fb7f.html

Also here is the specification of the Aironet Bridge I am using
http/www.cisco.com/en/US/products/hw/wireless/ps5279/products_data_sheet09186a008018495c.html

ConceptZone

G

#### Guest

##### Guest

On 3 Sep 2005 04:12:06 -0700, "ConceptZone" <ismail@conceptzone.net>
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/hw/wireless/ps5279/products_white_paper0900aecd801c4a88.shtml

See:
> http/www.cisco.com/en/US/products/hw/wireless/ps5279/products_technical_reference_chapter09186a00802a16cd.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/smbiz/wireless/approvals.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

+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.

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 jeffl@comix.santa-cruz.ca.us
150 Felker St #D http/www.LearnByDestroying.com
Santa Cruz CA 95060 http/802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

G

#### Guest

##### Guest

> 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.