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From: Dan Purgert <dan@djph.net>
Newsgroups: alt.os.linux,comp.sys.mac.system,microsoft.public.windowsxp.general,alt.comp.os.windows-10
Subject: Re: Curious how far your Wi-Fi access point is from your desktop
   computer
Date: Wed, 16 Oct 2019 13:54:13 -0000 (UTC)
Organization: A noiseless patient Spider
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Arlen _G_ Holder wrote:
> On Wed, 16 Oct 2019 03:06:46 -0000 (UTC), Dan Purgert wrote:
>
>> Usually around 30.  But that's because that's the legal limit for point
>> to multipoint intentional radiators.  You can only run your setup at the
>> EIRP you've stated if it's point-to-point.
>
> Hi Dan Purgert,
>
> Thanks for reminding us the rules are different for...
> o Point-to-MultiPoint [e.g., 2.4GHz is 36dBm (4watts)]
> o Point-to-Point [e.g., 2.4GHz could be as high as 158 dB]

No it can't. As per FCC 15.247("Operation within the bands 909-928 MHz,
2400-2483.5 MHz, and 5725-5850 MHz"),

  (b) The maximum peak conducted output power of the intentional
    radiator shall not exceed the following:
  (1)For frequency hopping systems operating in the 2400-2483.5 MHz
    band [...]: 1 watt. 

  (c) Operation with directional antenna gains greater that 6 dBi
  (1) Fixed point to point operation:
  (i) Systems operating in the 2400-2483.5 MHz band that are used
    exclusively for fixed, point-to-point operations may employ 
    transmitting antennas with directional gain greater than 6 dBi
    provided the maximum conducted output power of the intentional 
    radiator is reduced by 1 dB for every 3 dB that the directional 
    gain of the antenna exceeds 6 dBi.


That is, if you have a fixed point-to-point link (such as from a WISP
tower to a customer's premises), you can increase the antenna gain by 3
dB for every dB you reduce your conducted power.

Assuming we start from the legal limit (30 dBm conducted + 6 dBi
antenna), and ignoring any additional restrictions imposed elsewhere in
section 15 of the FCC rules (e.g. 15.209):

  - our first step is a 9 dBi antenna, with 29 dBm conducted, for a
    result of 38 dBm EIRP.

  - our tenth step is a 36 dBi antenna, with 20 dBm conducted, for a 
    result of 56 dBm EIRP.

  - our twentieth step is a 66 dBi antenna, with 10 dBm conducted, for 
    a result of 76 dBm EIRP.

  - our thirtieth step is a 96 dBi antenna, with 0 dBm conducted, for
    a result of 96 dBm EIRP.

At this point, we've generally nowhere else to go. Some radios may be
able to conduct at a few dBm below zero


> [...]
> So it's not just a single number.
> o But it's my understanding that the radio won't "let" you exceed limits
> (That understanding is literally from conversing with Ubiquiti support.)

The "lockouts" are based on what you give the radio as inputs.  Wrong
inputs = wrong lockouts. This is, of course, not possible to change on
the all-in-one units (Nanobeam, Nanostation), but any of the models with
removable radomes (Powerbeam, Litebeam) or antennas (Rocket) can be told
the wrong information.

> [...]
> There they discuss my radio, which turns out to be, for Paul an...
> o Ubiquiti PowerBeam M2 400, which is only 26 decibels of transmit 
> o into an 18dBi antenna, which is legal for point-to-multipoint

No, it is not.  The maximum EIRP of a point-to-multipoint intentional
radiator is 36 dBm (30 dBm conducted power + 6 dBi antenna; or a 1:1
correction thereto).


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-- 
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|_|_|O| Github: https://github.com/dpurgert
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