# 900 SM TX Power

If the 900 SM’s are only rated for 26dBm why can you set them to 28dBm?

jwcn wrote:
If the 900 SM's are only rated for 26dBm why can you set them to 28dBm?

They can be used at 28dbm if you have an 8dbi or less antenna.

The total EIRP must be 36dbm or less. With the "normal" 12dbi antenna, 26dBm is the legal limit.

Note that this also means if you have a higher-gain antenna like a 15dbi, you need to turn this down lower.

-forrest

Sure, they can be set at 28dBm but are they actually putting out 28dBm or 26dBm?

It’s been said before that the maximum output is 26dBm not 28

jwcn wrote:
Sure, they can be set at 28dBm but are they actually putting out 28dBm or 26dBm?

It's been said before that the maximum output is 26dBm not 28

They are actually putting out 28dBm.

If you don't believe me, try turning a SM up from 26 to 28 and notice the difference in the RSSI on the AP side...

-forrest
forrestc wrote:
[quote="jwcn":iucz4c9z]If the 900 SM's are only rated for 26dBm why can you set them to 28dBm?

They can be used at 28dbm if you have an 8dbi or less antenna.

The total EIRP must be 36dbm or less. With the "normal" 12dbi antenna, 26dBm is the legal limit.

Note that this also means if you have a higher-gain antenna like a 15dbi, you need to turn this down lower.

-forrest[/quote:iucz4c9z]

sorry to nit-pick, but 12+26=38 not 36...for an integrated 12db panel the max legal value for this is 24db.

24outputpower+12db(antenna)=36db max eirp..

I stand corrected.

jwelch wrote:
[quote="drdrew":2u96g0uc][quote="forrestc":2u96g0uc][quote="jwcn":2u96g0uc]If the 900 SM's are only rated for 26dBm why can you set them to 28dBm?

They can be used at 28dbm if you have an 8dbi or less antenna.

The total EIRP must be 36dbm or less. With the "normal" 12dbi antenna, 26dBm is the legal limit.

Note that this also means if you have a higher-gain antenna like a 15dbi, you need to turn this down lower.

-forrest[/quote:2u96g0uc]

sorry to nit-pick, but 12+26=38 not 36...for an integrated 12db panel the max legal value for this is 24db.

24outputpower+12db(antenna)=36db max eirp..[/quote:2u96g0uc]

The 900 (non-connectorized) has a 10dB integrated antenna[/quote:2u96g0uc]

thats an incorrect statement.. the 900 integrated units have a 12.5dBi antenna.

http://motorola.motowi4solutions.com/support/library/

go there & open the 900mhz document to verify if you wish...

When you figure ERP you do not add the gain of the antenna to the input power of the antenna. You multiply the gain of the antenna by the input power to the antenna.

A 12dbi antenna would have a multiplier of 16, since with every 3dbi increase in gain you double the ERP

So a 9dbi antenna would have a multiplier of 8, and a 12dbi antenna would have a multiplier of 16, a 17dbi antenna would have a multiplier of 50.

26 dbm = 400mw / 28 dbm = 631mw

9dbi antenna 8 x 400mw =3.2w =35dbm ---------8 x 631mw = 37dbm

12dbi antenna 16 x 400mw = 6.4w = 38dbm-----16 x 631mw = 40dbm

17dbi antenna 50 x 400mw = 20w = 43dbm------50 x 631mw = 45dbm

This is EIRP, it does not account of any loss in the system.

That is correct.