Cisco AP EIRP Calculation Examples
Used AP for these calculations is a Cisco AIR-AP1572EAC-E-K9 access point running IOS Version 15.3(3)JA8$ (8.0.133 MR3).
1. Browse for the EU Directive 1999/5/EC - Compliance Information document on the Cisco website for the specific access point.
2. Following tables are of importance in this document:
a. Table 1 - Max. Allowed EIRP for ETSI
b. Table 2 - Max TX power increments
Note*: The AP will lower the TX power in increments of 3dB. The max allowed TX power for this AP is 23dBm.
3. Used Formulas:
a. EIRP calculations
EIRP (dBm) = TX power (dBm) + antenna gain (dBi) – insertion loss (dB)
Ex. >>> 23dBm + 7dBi = 30dBm (we don’t care for insertion loss for these examples due to fixed antenna gains (cable loss and connector is already included)).
b. mW to dBm convertion
10 x log10 (mW) = dBm
Ex. >>> 10 x log10 (1mW) = 0dBm
4. Used Cisco Ios commands for AP config extract :
a. LAP-01772-01-0001-Smokey > show controllers dot11Radio 0 >> 2.4GHz radio
b. LAP-01772-01-0001-Smokey > show controllers dot11Radio 1 >> 5GHz radio
5. Configuration Example 1
Carrier Set: Belgium (BE) (-E)
Uniform Spreading Required: Yes
Configured Frequency: 5540 MHz Channel 108 (DFS enabled)
Configured TxPower: 16 dBm (Level Index 1)
Allowed Power Levels: 16 13 10 dBm
Allowed Client Power Levels: 16 13 10 dBm
Antenna: Rx[a b c d ]
Tx[a b c d ofdm all]
External Gain [Allowed 8, In Use 26] (dBi x 2) 10, In Use 26] (dBi x 2) 14, In Use 26] (dBi x 2) 16, In Use 26] (dBi x 2) 26, In Use 26] (dBi x 2) 28, In Use 26] (dBi x 2), Reported 26, Configured 26, In Use 26] (dBi x 2)
You can see in this example that the channel configured on the AP is 108 (5.540 GHz) which is located in the UNII2-ext band (Table 1). The max. EIRP for this band is 1000 mW or 30dBm (10 x log10 (1000). We statically configured the AP gain to 13dBi (26 increments of 0,5dBi). The AP auto chose the TX power level of 16 dBm (when configured on level index 1). See table 2 for allowed tx power increments.
TX power = 10 x log10 (200mW) = 23,01dBm
EIRP = 23,01dBm + 13dBi = 36,01dBm (higher than 30dBm)
TX power = 10 x log10 (100mW) = 20dBm (23dBm – 3dB)
EIRP = 20dBm + 13dBi = 33dBm (higher than 30dBm)
TX power = 10 x log10 (50mW) = 16.9897dBm (23dBm – 3dB – 3dB)
EIRP = 16.9897dBm + 13dBi = 29,9897dBm (lower than 30dBm)
6. Configuration Example 2
Carrier Set: Belgium (BE) (-E)
Uniform Spreading Required: Yes
Configured Frequency: 5540 MHz Channel 108 (DFS enabled)
Configured TxPower: 20 dBm (Level Index 1)
Allowed Power Levels: 20 17 14 11 8 dBm
Allowed Client Power Levels: 20 17 14 11 8 dBm
Antenna: Rx[a b c d ]
Tx[a b c d ofdm all]
External Gain [Allowed 8, In Use 14] (dBi x 2) 10, In Use 14] (dBi x 2) 14, In Use 14] (dBi x 2) 16, In Use 14] (dBi x 2) 26, In Use 14] (dBi x 2) 28, In Use 14] (dBi x 2), Reported 14, Configured 14, In Use 14] (dBi x 2)
You can see in this example that the channel configured on the AP is 108 (5.540 GHz) which is located in the UNII2-ext band (Table 1). The max. EIRP for this band is 1000 mW or 30dBm (10 x log10 (1000). We statically configured the AP gain to 7dBi (14 increments of 0,5dBi). The AP auto chose the TX power level of 20 dBm (when configured on level index 1). See table 2 for allowed tx power increments.
TX power = 10 x log10 (200mW) = 23,01dBm
EIRP = 23,01dBm + 7dBi = 30,01dBm (higher than 30dBm)
TX power = 10 x log10 (100mW) = 20dBm (23dBm – 3dB)
EIRP = 20dBm + 7dBi = 27dBm (lower than 30dBm)
7. Configuration Example 3
Carrier Set: Belgium (BE) (-E)
Uniform Spreading Required: Yes
Configured Frequency: 5540 MHz Channel 108 (DFS enabled)
Configured TxPower: 23 dBm (Level Index 1)
Allowed Power Levels: 23 20 17 14 11 8 dBm
Allowed Client Power Levels: 23 20 17 14 11 8 dBm
Antenna: Rx[a b c d ]
Tx[a b c d ofdm all]
External Gain [Allowed 8, In Use 8] (dBi x 2) 10, In Use 8] (dBi x 2) 14, In Use 8] (dBi x 2) 16, In Use 8] (dBi x 2) 26, In Use 8] (dBi x 2) 28, In Use 8] (dBi x 2), Reported 8, Configured 8, In Use 8] (dBi x 2)
You can see in this example that the channel configured on the AP is 108 (5.540 GHz) which is located in the UNII2-ext band (Table 1). The max. EIRP for this band is 1000 mW or 30dBm (10 x log10 (1000). We statically configured the AP gain to 4dBi (8 increments of 0,5dBi). The AP auto chose the TX power level of 23 dBm (when configured on level index 1). See table 2 for allowed tx power increments.
TX power = 10 x log10 (200mW) = 23,01dBm (highest TX power possible)
EIRP = 23,01dBm + 4dBi = 27,01dBm (lower than 30dBm)
8. Configuration Example 4
Carrier Set: Belgium (BE) (-E)
Uniform Spreading Required: Yes
Configured Frequency: 5540 MHz Channel 108 (DFS enabled)
Configured TxPower: 23 dBm (Level Index 1)
Allowed Power Levels: 23 20 17 14 11 8 dBm
Allowed Client Power Levels: 23 20 17 14 11 8 dBm
Antenna: Rx[a b c d ]
Tx[a b c d ofdm all]
External Gain [Allowed 8, In Use 8] (dBi x 2) 10, In Use 8] (dBi x 2) 14, In Use 8] (dBi x 2) 16, In Use 8] (dBi x 2) 26, In Use 8] (dBi x 2) 28, In Use 8] (dBi x 2), Reported 0, Configured 0, In Use 8] (dBi x 2)
You can see in this example that the channel configured on the AP is 108 (5.540 GHz) which is located in the UNII2-ext band (Table 1). The max. EIRP for this band is 1000 mW or 30dBm (10 x log10 (1000). We statically configured the AP gain to 0dBi (the AP automatic antenna detection chose 4dBm). The AP auto chose the TX power level of 23 dBm (when configured on level index 1). See table 2 for allowed tx power increments.
TX power = 10 x log10 (200mW) = 23,01dBm (highest TX power possible)
EIRP = 23,01dBm + 4dBi = 27,01dBm (lower than 30dBm)
9. Conclusion
a. Example 1: When you select a 13dBi antenna, the AP selects the closest power level so that EIRP won’t go over 30dBm – hence 16dBm (in fact 10 x log10 (50mW) = 16.989700043360187dBm.
The AP showing 16dBm instead of 17dBm is due to operation rounding up to closest integer.
b. Example 2: When you select a 7dBi antenna, the AP selects the closest power level so that EIRP won’t go over 30dBm – hence 20dBm. Selecting 23dBm is not possible since (10 x log10 (200) = 23.010299956639813).
The AP cannot go over the max allowed EIRP level (even for 0.01dBm – 1.01mW). In that case the AP won’t meet compliancy requirements. Since only power decrements of 3dB are allowed, lowering the transmit power to 20dBm will be selected.
c. Example 3: When you select a 4dBi antenna, the AP can safely select 23dBm as transmit power since resulting EIRP will be 27dBm which is below the maximum allowed EIRP of 30dBm. Remember that we cannot go higher then 23dBm.
d. Example 4: Same as #3, but here the AP detected that a 4dBi antenna is installed, though not configured – automatic antenna detection may be inaccurate though.
