B24 collocation with UBNT AF-24


Moving existing conversations to the new B24 category

B24 collocation with UBNT Air Fiber

Are there any best practices for collocating our new B24 with our existing Ubiquiti Air Fiber?


Excellent question, @Corey2.

Unfortunately our GPS sync does not communicate with UBNT GPS sync. You would need to use a different channel or get far enough away from the AirFiber to use the same channel.

From the testing I’ve seen, AirFiber24 has a lot of backscatter which would cause you interference, even when facing away from the AF24. @Faisal I believe has a collocated B24 and AF24, so he might be able to add additional information.


Do they interfere with each other ? yes… if you see our mount picture,… B24 mounted a couple of feet from AF24 on the same link path… we had to shutdown the AF24… one might be able to make the AF24 co-exist with B24 if AF24 is setup to half duplex, and B24 is setup with smaller channel of 1FD mode… … We have other AF24’s on the AP side but not very close and pointing in other directions… incidentally we discovered (comparing with another link) that our noise floor is 5db higher … so yes there is interference …If I was to summarize… speaking very loosely if you have a 5ft or higher separation, and the AF24 is not pointing in the same direction, you should be fine… (if it it someone else’s AF24, then you may have some modulation wobble… if it is your AF24, you might want to replace it with a B24 for a happy co-existence ! :wink: )



Hi Dustin:

Ya, the B24 dies when the AF24 is fired up. We got the B24 link up and running when we turned off the AF.

The way AF works is that the MU transmits on a 100 MHz channel at 24.2 to the RU and the RU then receives on 24.2 and transmits back to the MU on 24.1.

The RU transmits on a 100 MHz channel at 24.1 and the MU receives on 24.1 and visa versa.

This scenario creates an open channel at 24.1 and 24.2 depending on which side you are on.

For example, when the AF MU is transmitting on 24.2, the B24 at the same location doesn’t see anything on 24.1 and visa versa on the RU side.

If the B24 could transmit on one 100 MHz channel and listen on the other, rather than duplexing the transmission across both channels, theoretically, the B24 could coexist with an Air Fiber24 just using the opposite channel depending on the location.

If we understand correctly, this would then not require the GPS coordination between the two different types of units.

We would really like to use the B24 as a redundant link for the Air Fiber but as it sits right now, we have to shut off the AF to use the B24 and both units take a bit of time to wake up and run. So, we can’t use STP to perform the redundant switch.



Hi Dustin:

Have there been thought put into the scenario I mentioned below?

@Faisal, thank you for your input. Our system is laid out just like your picture shows and, yes, the B24 stops working when we fire up the AF24.

Because the AF24 transmits on one 100 MHz channel (24.1) and receives on the other (24.2), it seems that if the B24 would operate similarly, rather than TX and RX spread across 24.1 & 24.2, we could set the B24 and AF24 to TX/RX opposite each other and they could coexist. We don’t ‘see’ the local AF24 signal on the B24 spectrum so its FTB ratio is pretty good. We only see the remote AF24 signal.

Thank you for your comments


Hi @Corey2,

Because of the way the B24 is designed, it would be pretty much impossible to do this. You could try 1x20/40/80 FD mode and choose one frequency on one side of the link and another on the other side of the link.


Hi Dustin:

We tried one frequency on either side of the link and, you’re right, it didn’t’ work concurrently with the AF24.

This is just disappointing as we purchased the B24 to offer STP redundancy for the AF24 link and it won’t work that way. It seems like it should given the use of frequencies on either side of the AF24 link. Unfortunate.

Please keep us in mind should anything change in this regard.

Thank you for your thoughts.


@Corey2 With the FD mode on the AF24 utilizing a frequency scheme with 100 MHz channels centered around 24.1 GHz and 24.2 GHz, one for Tx the other for Rx, it would be impossible to co-locate a B24 with the AF-24 unless you can utilize smaller channel widths on the AF-24 and park the channels in different parts of the spectrum. With a co-located B24 and AF24 with one operating in Rx mode and the other in Tx mode on the same channel, the Transmitting radio will flood/saturate the Receiving radio.

Without any sync - a transmitting radio look like interference

BTW - Two AirFiber 24 radios will interfere with each other as well. You can sync up to 8 B24 radios around a deployment site… and with our new 20 MHz wide channel support coming soon, you can sync up to 8 co-linear links


So it all boils down to no industry standard for Sync. Not Mimosa’s fault, but it seems like a system that creates “Vendor Lock in.” (at least on towers)

Unfortunately there does not seem to be a way to get various wireless radio makers onboard with a single protocol, though maybe an agreement on timing might be possible? Everyone is using the same GPS satellites, everyone says x time is the start of all TDMA Windows (preferably midnight 1970-01-01 or something else nerdy) and then let operators set window sizes and Traffic split to not interfere between equipment. Though this could be a pipe dream that cant happen because of weird protocol issues. Though I bet the masses would love it.


@William5 There is a bit more to it. In addition to timing from GPS, to sync you have to coordinate TDMA Timing windows for Tx/Rx, UL/DL ratios, and any contention period windowing required for request to sent additional data vs. what was allocated during the slot times.
This essentially means new protocol development work for everyone except the vendor who’s timing plan is used to standardize on.
While a noble idea… it’s hard to herd the cats into this chute.

We have been trying to coordinate access sync with Cambium for some time, but we can’t get them to bite.


Well at least you are trying, I figured there would be more to it then basic window timing. The compatibility mode would probably have to be stringent on transmissions during timing windows and so many other issues that it just would not happen.

Sad to say, but I guess nobody complains that they can’t use their VW bug steering wheel in their Chevy Impala. (though if you go enough years back you probably could…) I am glad to hear that you guys are trying to play nice with Cambium. I will be expecting something to come down the line about the time Router OS 7 comes out…:grin:


Is that a wonder? Every vendor like to keep his buyer to himself. TDMA was the perfect marketing tool to that make ubnt big. Once you made a decision it becomes costly to go back on that one… Who is smiling here. All vendors are in the game for market share. Once you’ve got some they’re reluctant to give it away…


It seems that most people use the AF24 in full duplex mode, where downlink is either 24.1GHz (100MHz wide channel) or 24.2GHz (also 100MHz channel), and uplink is the other of those two channels.

Now with the B24 (unfortunately, imho) there is no support for full duplex. However, the AF24 does support half-duplex and has inbuilt GPS sync. So if you are trying to co-locate a B24 and an AF24, there would seem to be two things worth trying, probably both at once:

1 - separation, both vertical/horizontal and angular.

2 - set the AF24 to half duplex and 75% “Master TX Duty Cycle”, the B24 to 75/25, and experiment to see if there’s any frequency arrangement on the B24 where they don’t stomp on each other.

The AF24 appears to always be 100MHz channels, one up and one down. (makes sense for full duplex, but I wish they supported other channel widths) So the trick is setting up where the downlink data from one of the links doesn’t overlap (both frequency and TDMA cycle) with the uplink data on the other link. With one full-duplex link and one TDMA the only way to achieve this is frequency separation, but with both set to TDMA and the same duty cycle it MAY be possible with freq overlaps. (depends on how each structure their TDMA frame relative to the sync pulse)

I have no idea what the impact of the switch to HD on the AF24 will be, have never tested it, but certainly it will mean higher latency and lower capacity.



What would be the suggested vertical separation between an AF24 and a B24.

Note: We are replacing a AF24 that died with the B24 and was in the exact same spot.


Our suggested spacing is 10ft, but I can see that’s not going to happen. As long as your collocated antennas are taking into account any type of side lobes (B24s need at least 30 degrees of seperation between each other, I believe AF24 needs more than 45 degrees), you should be ok.

Maybe someone who has collocated AF24 and B24 could weigh in. I know for sure @Faisal has done this, but he certainly couldn’t have them facing the same direction.


Dustin has laid out the parameters, in terms of vertical and angular separation. If you are going to run a AF24 and B24 in the same direction next to each other (on top of each other), you will have to do one of the following:- 1) Turn off the AF24 :slight_smile: or 2) configure both radios to use less spectrum and thus not trample on each other !.. (otherwise the link ain’t going to happen ! :slight_smile:


Well they are on top of each other, however as you can see in the pic above they are not facing the same direction. Here are my link results. And yes it’s rather hot in Dallas today.


Bleck, that looks horrible (heat wise) the link looks great.