• By Tony-T - edited: August 1, 2017

    Hello There

    Do the Beacon and Neighbor message frames break the legal (EIRP) limits put in place by the legislators in our respective regions, when using high gain antennas?

    As Beacon and Neighbor messages (and maybe more that I am not aware of) are sent at max power - will this break the legal max EIRP rules

    My situation is-

    Industrial environment (big freezers that conform to Mr Faraday's rules)

    Meraki MR72 + MA ANT-11 (5gHz / 14dBi) & MA_ANT 13 (2.4GHz / 11dBi)

    AP max output is +20dBm / plan to assign power to +8dBm

    On 5GHz:

    Max Tx power: 20dBm + 14dB = 34dBm / 2, 512mW   <- Oh Dear, a little 'over the top'

    Set Tx power:  8dBm + 14dB = +22dBm / 158mW  <- WooHoo I'm legal

    Indoor max legal Tx power on 5GHz UNII 1 is 200mW EIRP (in Australia at least)

    But it looks like the 'Tx at max power' frames will be transmitted at 2,512mW EIRP - this being true, Is it a problem?



  • By Howard - edited: August 1, 2017

    I looked at the Meraki website regarding this AP..  In general, it looks like they are touting Bluetooth Low Energy (BT-LE) Beacons.

    First, if these are the beacons you are worried about don't worry. - there is no BT in the 5GHz range.    

    Also, I can (almost) guarantee you that the BT Beacons will be at a much-much lower power level..

    If not , please clarify, as I could not find anything regarding higher power beacons.

    Whoever is selecting and installing you AP's and antennas should be familiar with all the siting rules in your locale.

  • Hello Howard

    While this AP is Bluetooth capable, I am referring to WiFi 802.11 transmissions.

    I believe that Beacon Frames and RRM Neighbor message frames (and maybe others) are transmitted at maximum tx power and at the lowest supported data rate (temporarily over-riding the Tx power level set in software).

    Accepting that the above statement is true, then the planned MR72 (with high gain antennas) will be set to a Tx level of +8dBm (or just below) and will operate at that Tx level for the most part, but would transmit at +20dBm when the Beacon & RRM Neighbor message frames are 'sent', and that looks to be quite a bit above the indoor maximum legal EIRP limit.

    In essence:

    Normal WLAN traffic would be transmitted at a Tx level +8dBm from the AP (nice and legal)

    Beacon frames (etc) look like they will be transmitted at a Tx level +20dBm from the AP (potentially well above the legal EIRP level)

    I hope what I have written above has more clarity

    (this is kinda "doing my head in", but am enjoying the challenge)



  • You are correct about the 8 dBm setting being preferred.  I don't think you'll have to worry about the maximum legal power level being exceeded.

    I do not know of any AP's that use different power levels for particular Frame types.   They might however, change the power level for different rates - ( though it requires more work by the radio designer and ends up being more work to insure that compliance requirements are met.)

    Everything sent at the same rate, will be sent at the same power level.   As noted, lower rates could, in fact,  be sent with slightly higher power levels depending on the radio manufacturers design, but it would only be by a few dB per step.  

    Beacons are sent at the lowest Basic rate, which is not necessarily the same as the lowest Supported rate.

    BTW, it is now very common to completely disable the lowest rates to limit your cell sizes and AP range.

    You should be able to specify both the Basic and the Supported rates individually.

    You also don't have to leave RRM completely un-tethered - you can override the power range it allows.

  • Tony,

    Take a look at this chain, and Devins video on RRM, if you haven't already.

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