I finally had a chance to figure out the discrepancy between radio power
readings in the 2.4 GHz band. I've often heard about people getting
significantly reduced signal when switching from airMAX to ePMP on 2.4
GHz.. but other people see no difference. In my case, I found a drop of
about 7 dB going from airMAX to ePMP on a particular PTP link with matched
settings running 5 MHz channels, but an increase in throughput (which
really made me want to figure out what was going on).

Following some early morning testing, it turns out: ePMP is reporting
received power while airMAX is actually reporting receive spectral density
with units dBm/20MHz.

As a result, if you swap radios from airMAX to ePMP when running 20 MHz
channels, you should little to no change at all. If you are running 10 MHz
channels, however, you should expect about 3 dB reduction in reported
signal, and if running 5 MHz channels, you should see about 6 dB reduction
in reported signal. [If you are running 40 MHz channels, you should see an
increase of about 3 dB, but please don't run 40 MHz channels in 2.4 GHz.]
These reductions are not the result of weaker performance, but simply
different units in the signal bar.

On a side note relative to poor ePMP performance... ePMP has had a firmware
issue with calculating output power in FCC areas resulting in lower than
allowed power output. I've been questioning them about this, and they tell
me the correct output power calculations should be in the "next firmware".
Once this is fixed, weaker customers should have a better chance of linking
up.

[Also, I should note the AF-2X radios also report received power like the
ePMP.]

-Chris

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