airFiber - Output Power Needed to Achieve Desired Modulation


Overview


This article includes information needed to determine the signal strength necessary to achieve different modulations.


Table of Contents


  1. Introduction
  2. Suggested Maximum Tx Power
  3. Sensitivity

Introduction


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In order to achieve certain modulation, enough signal strength is necessary to keep it stable. Radio sensitivity information is available in our products' data sheets (downloadable at the bottom of each product page in www.ubnt.com). However, not all users know that the output power also determines what the maximum modulation rate is. Our airFiber 5X is a very powerful device: every dB will matter to get maximum throughput and optimize efficiency.

The following two tables will help with this: the first shows suggested maximum Tx Power and the second, the radio sensitivity depending on channel width and modulation.


Suggested Maximum Tx Power


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NOTE: Remember that maximum output power depends on country code and frequency.

Suggested Max Tx Power:

 Modulation Output Power
8x 19-20 dBm
6x  21-22 dBm
4x  23-24 dBm
1-2x  26 dBm
1/4x 26 dBm

From the table above we can conclude that to achieve up to 8x modulation it's highly recommended to use output power up to 20dBm. If higher levels are used, for example 21dBm output power, it's possible that you'd only get up to 6X.


Sensitivity


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Radio sensitivity depends on channel width and modulation, for example if you want to get 8X modulation using 30MHz channel you need a received signal strength of -62dBm or better (like -60dBm, -55dBm, etc...).

User Tip: It's a good practice to keep a certain fade margin to prepare for weather changes or other situations that could temporarily affect your link. Recommended fade margins depend on your area and link distance. In most cases, it's recommended to keep at least 5dBm of fade margin.

 

BW (MHz)

Rate

RX Power (dBm)

50

8x

-60

50

6x

-67

50

4x

-74

50

2x

-81

50

1x

-83

 

 

 

40

8x

-61

40

6x

-68

40

4x

-75

40

2x

-82

40

1x

-84

 

 

 

30

8x

-62

30

6x

-69

30

4x

-76

30

2x

-83

30

1x

-85

 

 

 

20

8x

-64

20

6x

-71

20

4x

-78

20

2x

-85

20

1x

-87

 

 

 

10

8x

-66

10

6x

-74

10

4x

-81

10

2x

-88

10

1x

-90


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