Why is the transmit power stuck at 10 dBM regardless of what I set them to?

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  • Updated 11 months ago
We recently replaced the Cisco APs in our high school with AP550's  We chose them specifically because of the programmable radios.  In most classrooms we have both set to 5GHz.  In a few locations, where coverage is more an issue than density, we have them set as 2.4/5.  Most classrooms are set to auto channel and auto power.  But the spots with coverage issues (guidance offices and the like) we have the power set to 15 or 20.

The radio profiles are both set to 20dBm as max power.   When I look at HMOL, every single AP550 shows the transmit power at 10 dBm regardless of what the device config is set to.  I don't seem to have this problem with our AP330's.  Any thoughts?
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Posted 11 months ago

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Edwin Boesten

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I had the same problem, my quick "fix" was to roll the AP back to firmware 8.0r1.
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Maybe I need to upgrade.  I am running HiveOS 7.0r3 Tower.138627.  I'll have to look for the release notes.
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Mike Kouri, Official Rep

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It's a display issue, the devices ARE transmitting at the maximum allowed power for your regulatory region. We changed the output in the CLI in HiveOS 8.1r1 based on feedback we have received over the years, to try and make it more intelligible. However, the GUI changes didn't happen at the same time.

Assume you're in the UK using channel 36. The regulatory region says that 23dBm is the max for that channel, and you say transmit at 20. What actually has always happened under the sheets was that we would take that EIRP limit of 23dBm, subtract around 6dBi for the antenna gain, subtract about another 6dBi for the 4 Tx chains gain, and subtract about 1 to 2dB for a safety-net (because not all transmitters are calibrated identically), and arrive at around 10dB conducted that our chip would use to achieve the 23dB EIRP allowed.

Here's a sample of the new CLI output, I've bolded the changes:

UK1-Basement#show int w1 | inc power

IDP=Intrusion detection and prevention; BGSCAN=background scan; PS=Power save;

EIRP=Effective Isotropic Radiated Power (Transmit Power + Max Antenna Gain + Max TX Chains Gain);

Freq(Chan)=5180Mhz(36); EIRP power=23.02*dBm(11dBm + 6.00dBi + 6.02dBi); Diversity=enabled;

Tx range=300m; Noise floor=-95dBm; Tx power control=disabled;

OFDM 20Mhz power: Board limit=20dBm; Regulatory limit=11dBm;

Please note that your AP330s are still on HiveOS 6.5r8 or earlier, so they did not pick up this change in the CLI output (nor will they).