Good information. Thanks for sharing.
------ Original Message ------
From: "Christopher Gray" <cg...@graytechsoftware.com>
To: af@afmug.com
Sent: 9/21/2016 7:17:59 AM
Subject: [AFMUG] Power Readings on 2.4 GHz airMAX / ePMP
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
