How many decibels does this router radio REALLY output?

How many decibels does the router/radio below really output? ('cuz 26 + 18 is too high)
In the before-and-after krack-update screenshot below, I'm confused because the radio says transmit power is 26dBm into a built-in 18dBi dish antenna, so the EIRP of the stock unit set for the USA would be too high at 26+18DdBm in the USA.
And yet it's all set to the defaults (I didn't change the transmit or antenna value since it's the stock unit that comes with the antenna).
BEFORE: <
http://wetakepic.com/images/2017/10/29/01_PB400_firmware_update_krack.jpg

AFTER: <
http://wetakepic.com/images/2017/10/29/14_PB400_firmware_update_krack.jpg

Of course, the AirOS firmware could secretly throttle the EIRP to 30dBM (or whatever the USA legal limit is); but why would AirOS report bogus number then?
What are those decibel numbers in AirOS actually *telling* me?
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On Sun, 29 Oct 2017 16:42:22 +0000 (UTC), harry newton

Are you doing point to multipoint or point to point?
<https://www.air802.com/fcc-rules-and-regulations.html
5GHz is different quite different. Might be helpful if you describe what you're using for hardware, what band you're using, and your wireless network topology.

One of the dangers of updating firmware is that the saved or stored values might not work with the new firmware if they've shifted memory location between versions. This is almost guaranteed for major revision changes in firmware. Less so for minor changes. When in doubt, print your your settings, reset the router, and manually setup the numbers. Krack firemare tweeks seem to be a rush job and fall in the category of "customer tested software".
You mention that "it's all set to the defaults" which is rather ambiguous. Did you reset the router after installing the firmware update?
Busy patching the roof today before the sky falls on me tonite.
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Jeff Liebermann snipped-for-privacy@cruzio.com
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He who is Jeff Liebermann said on Sun, 29 Oct 2017 12:41:28 -0700:

Thanks Jeff.
Given the 2.4 GHz antenna dish is 18 dBi, the chart says the max is a. Point to multipoint (18dBm or 63mW transmit) into (18dBi antenna) = (36 decibels or 4 watts)
b. Point to point (26dBm or 400mW transmit) into (18dBi antenna) = (44 decibels or 25 watts)
The radio is set up as an access point, exactly how you suggested Rod Speed set up his antenna outside his house to feed his neighbor Wi-Fi where his neighbor is only a few hundred feet away line of sight.
So I'm overdriving the radio by accident, I think. I thought they throttled themselves so that they'd never exceed the limit.

I have plenty of 5GHz Ubiquiti equipment (Rocket M5, for example, with a 30dBM dish), but this particular radio is one of my smaller ones, which is the Ubiquiti PowerBeam M2 400, which is only 26 decibels of transmit into an 18dBi antenna.
But even so, it has no problem getting to the legal limit it seems, where it must be defaulting to the legal limit for point to point even though it's set up as an access point hanging off a wired router acting as a repeater.
It only has to paint the barn with 2.4GHz WiFi to feed the cameras which are about a half kilometer away, which is nothing for this type of WiFi radio.

The radio rebooted itself after the firmware update.
What I mean by defaults is the radio is set up to be an access point at a certain IP address in bridge mode, but that's all I set. The rest is whatever defaulted after I set it.
So I didn't touch the antenna setting. Nor did I touch transmit power.
So it *defaulted* to the 44 Watts, which, for a home radio, is overkill unless I'm going 10 miles but it's not even half a mile that I'm going.
So I'll dial down the transmit power. Thanks.
NOTE: For those reading this, if you need an access point to paint an area between hundreds of feet and a couple of miles away with 2.4GHz or 5GHz WiFi signal, you can get Ubiquiti or Mikrotik radios for about the same price as you paid for your last home router - but which are so much more powerful (aka directional) than a radio with an omni, that it isn't funny.

Good luck with the roof!
Our power went out again yesterday (it goes out once a month) and we didn't even have much wind coming up from your side of the ocean.
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On Sun, 29 Oct 2017 21:35:35 +0000 (UTC), harry newton

I deduce by reading between your lines that you have an unspecified model 2.4Ghz radio and that you're using it in point-to-multipoint topology. Therefore, you're limited to 4 watts EIRP which translates into +26dBm into an 18dBi dish.

As far as I know, there's no connection between the transmit power and the mode of operation. Since the radio has no way to know what gain antenna is attached, it has no way to determine if the radio is used in accordance with 15.247. Setting up your Ubiquiti for bridging, which is what's normally used for point to point, should not have any effect on the transmit power.
Note that if this were a cellular system, which has ATC (automagic transmitter control), the SNR (signal to noise radio) from the receiver at the other end of the link would be reported back to the transmit radio and adjusted for the minimum RF level necessary to maintain a decent BER (bit error rate) or PER (packet error rate). However, wi-fi is not cellular, so forget about doing it the way you've been guessing that it works.

Reboot is NOT the same as reset to defaults. When you reboot, all it does is unload the current setting from working memory, and reload the saved settings from NVRAM into working memory. When you update the firmware, there's no guarantee the setting saved in NVRAM are going to work correctly.

Let me make this really simple. If you're radio is going goofy things after a firmware update, punch the reset button and put everything back to the factory defaults. Then, configure it to your favorite working numbers and see if the problem goes away.

Everything you do seems to be overkill.

Dial, as in a knob and potentiometer? How quaint.

I think I have all the potential leaks plugged. Of course, I've been saying the same thing for last 15 years or so.
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He who is Jeff Liebermann said on Mon, 30 Oct 2017 19:28:04 -0700:

Yes. I was setting up an access point. Your information helps because I want to stay legal.
For example, since a neighbor 15 miles away (by road) lost her Internet yesterday in the Santa Cruz Mountains, I temporarily set her up using this spare Rocket M2 I had lying around outside gathering leaves & rust: <
http://wetakepic.com/images/2017/11/01/wifi3.jpg
It won't hold up against a windstorm as all I did was hand bolt it to the top of a wooden stepladder just outside her house, on the ground, near enough for the only (albeit short) Ethernet cord she had to reach the POE injector just inside the house. <
http://wetakepic.com/images/2017/11/01/wifi4.jpg
Luckily, as you know, the weather is calm these days out here so it will hold up until her ISP gets around to fixing the blown access point she was connecting to. Meanwhile, we're getting pretty good (-60dB) signal pointing to an access point that is over 3 miles (over 5 kilometers) away with this temporary rig. <
http://wetakepic.com/images/2017/11/01/wifi_2.jpg

This is good information becuase, for some reason (the forums?) I was under teh impression tha tthe radios were "hard coded" to not exceed the legal EIRP under any circumstances.
Yet, as can be seen in the screenshot below, this Ubiquiti Rocket M2 I temporarily set up for my neighbor miles away, is transmitting at 24 dBm into a dish that is 24 dBi, for a whopping calculation EIRP of 48 dBm. <
http://wetakepic.com/images/2017/11/01/wifi.jpg

In this case of the temporary setup, the measured noise is about -84 dBm, with a signal of -60 dBm, so we have a headroom of about 24dBm, which is way more than the 10 dBm to 15 dBm I find out, empirically, that seems to be the minimum required for a stable connection.

I agree. In fact, I sometimes get *better* performance when I update the firmware, and sometimes *worse* (especially when they change how the radio reacts to denial-of-service attacks which consume the CPU bandwidth (it seems).
I had to talk to my ISP to get him to block certain IP addresses on his side, instead of me having to do so one by one on my side.
But I agree, there are three things that are different: a. Merely rebooting the radio (aka power cycling) b. Resetting the radio to factory default (aka factory settings) c. Updating the radio firmware (aka the operating system)

I agree. It's even *easier* than that because I save the configuration files, so, in the end, all I have to do (for Ubiquiti equipment) is press the reset button on the POE injector for about 15 seconds (until all the lights flash on the radio), and voila! Factory settings.
Then I change my PC laptop to the 192.168.1.xx subnet, taking care not to use 192.168.1.0, 192.168.1.1, and 192.168.1.255, or 192.168.1.20.
Then I log into the radio at http://192.168.1.20 with a username and password of "ubnt" "ubnt", and load the previously saved configuration file.
I love that the Ubiquiti equipment defaults to station mode, which means you can plug it into any computer Ethernet port where it becomes your Wi-Fi connection capable of connecting your laptop to an access point *miles* away (depending on the access point of course) where you see a desktop connected to the access point over 3 miles (over 5 kilometers) away.

Let's hope this winter is wet, but I could do with a lot less rain than we had *last* winter, where our power went out every two weeks or so, for months!
You're a little closer to civilization than I am, but we're both in the same weather patterns.
Thanks for your helpful advice!
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On Wed, 1 Nov 2017 13:59:19 +0000 (UTC), harry newton

The maximum transmit power and operating channels of the radio are controlled by the country code setting. Anything sold in the USA is suppose to be "locked" to US power limits: <https://www.cisco.com/c/en/us/td/docs/wireless/wcs/3-2/configuration/guide/wcscfg32/wcscod.pdf >Yet, as can be seen in the screenshot below, this Ubiquiti Rocket M2 I

If it's point to point, that's legal. For fixed Point-to-Point it's 1 watt (+30 dBm) minus 1 dB for each 3 dB of antenna gain greater than 6 dBi. FCC Part 15.247(b) and (c), and Part 15.407(a).

The fade margin, headroom, SOM (system operating margin), Eb/No (energy per bit / spectral noise density), SNR (signal to noise ratio), or whatever you wish to call it, varies with the data rate. The faster you go, the more fade margin you need for a constant BER (bit error rate) or PER (packet error rate). It also varies with modulation method. <http://www.eletrica.ufpr.br/evelio/TE111/Eb_N0.pdf From my archives: Minimum signal to noise ratio (Eb/No) for various speeds at a BER = 10E-5 using 802.11b and 802.11g Speed SNR(dB) 11 6.99 5.5 5.98 2 1.59 1 -2.92 54 24.6 48 24.1 36 18.8 24 17.0 18 10.8 12 9.0 9 7.8 6 6.0

Nope. I don't think you understand the problem. The structure of the configuration files might change between firmware versions. Often, it's something subtle, like the length of the field length in an array. If you restore the previously saved configuration file, you're putting everything back the way it was before it became screwed up. The idea is to use the new and improved structure, from the upgraded firmware, not whatever is lurking in your saved config file. To play it safe, after a few surprises, I only restore config files to the a device with the same firmware that was used to create it.
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He who is Jeff Liebermann said on Wed, 01 Nov 2017 08:45:13 -0700:

Thanks for that chart Jeff, as my Ubiquiti equipment, bought in the USA whole, can only set itself to the USA, Canada, and, I think, Mexico (I'd have to look) whereas my similar Mikrotik equipment (but bought as boards and assembled in the USA) can be set to any one of 200 odd countries.

That explains the enigma, because it's certainly *saying* the EIRP is 48 decibels! <
http://wetakepic.com/images/2017/11/01/wifi.jpg

Yes. I know. And I know you know. I've seen all the datasheets, as have you. For others though, here's a datasheet for just the radio part of my Ubiquiti Rocket M2 setup (where the antenna is 24 dBi added to that). <https://dl.ubnt.com/datasheets/rocketm/RocketM_DS.pdf

Yup. As a rule of thumb, I look for 12 to 15 dBm "headroom" to solve all those complexities. :)

Heh heh .... looking at the author's comments, I knew an electrical engineer pHd named Bob Pease in the valley.
Same guy?
Tall. Thin. Sharp featured. Nerdy as hell. Don't ever get caught in a corner with the guy discussing diffraction of electromagnetic beams!
Not like you or me. You looked like a hippy parks guy, while I look like a pocket-protected balding computer nerd.

Well, what's interesting about your numbers is that sometimes it needed a *lot* less than my rule of thumb, and sometimes it needed a lot more.
Sigh. Such are rules of thumb. Luckily, the setup I showed has the requisite headroom to handle the values in your chart!

OK. I belatedly get it. While it has never happened to me, I belatedly understand your heart-felt advice to be wary of such changes.
Since I only use a small subset of Ubiquiti and Mikrotik stuff, and mostly a very small subset of Ubiquiti radios, in practice, that hasn't happened *to me*.
It has happened to me on Android, Linux, iOS, Windows, etc., but not on AirOS or WinBox, yet.

See above. I agree. In principle. Luckily, setting up a radio is easy most of the time. a. It's either an access point, b. Or it's a station (e.g., the barn cam)

You have far too much real-world experience with such radios! I have less experience in what can go wrong!
I appreciate the clarifying advice! Thanks.
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