Minimum sector spacing for frequency reuse?

Within my company's network we have numerous small-scale sites with four ePMP5 GPS sectors mounted directly to a single guyed pole. In the current arrangement, there's only about 1ft of separation between each back-to-back pair and my understanding is that this is too close for frequency reuse to function properly.

In my lurking I found a post stating that there should be at least 3ft between each sector antenna, but I was wondering if anyone around here has gotten it to work with smaller spacing and has found any sort of mounting solution that would at least get us closer to that recommended distance.

I've been eying RF Armor's 4-gang cluster mount, but the datasheet doesn't include any measurements (or anything aside from a couple pictures for that matter) so I don't know whether it would even fit the mounting brackets for the RF Element ePMP sectors.

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Which antennas are you using for this? Assuming you're using Cambium antennas, you might be able to get away with adding additional shielding along with turning down the AP's TX power a bit.

All that being said, I think your back to back frequency reuse would probably work.


Hi Fezdmn,  Well, much of the 'magic' in the ePMP is ways to mitigate self interference - which can substantially improve performance.  The ability for the AP's to sync via GPS is pretty much key to the way the ePMP works, and syncing is the 'magic' of reducing self-interference.

So - if you understand the way that is achieved, in the simplest form, all four of your AP's will transmit at the same time, and then they will all listen to their clients at the same time. That helps dramatically with self interference, since AP-North isn't trying to listed to some distant client at the same instanat that AP-West is transmitting - which would overwhelm any hope of AP-North hearing it's clients.  That is the self-interference nightmare that most systems have, but with GPS Syncing (and by having the same download/upload ratios, the same frame siz, the same distance setting, etc) then all the AP's can be exactly synced for when they TX and when they RX.

Now - from the client side of things, it's also important to mitigate self-interference as well. That is automatically greatly helped because of the syncing - so that no client is trying to transmit to it's AP at the same time as any other AP is transmitting and deafening the target AP. But, it's also important to issolate each AP as much as possible from them being heard by the clients of the other AP's. You can do that by channel separation, and you can also do that by good front-back ratios, and by physical separation and shielding and so on.

So - if for example, you have a client conneceted to 'north' and if he's about 45 degrees off the beam, he'll hear 'north' and 'west' about the same - and it's important to have some channel separation so that 'north' and 'west' don't screw each other up. Likewise, if you have a client right in the middle of the beam 'north' and another right in the middle of the beam on 'south' and if you're doing frequency resuse, then it's important to have 'north' and 'south' issolated from each other as much as posisble. If you don't, then the client on 'south' that hears 'south' as a -60 and if it also hears 'north' as a -70 - then you've defeated much of Cambium's 'magic'. I think Cambium recommends >30 dBm of issolation - so that's Front-Back ratios and shielding and physical separation and so on. That way, the client on 'south' hear 'south' at a -60, and it'll only hear 'north' at a -90 and all is well and right and just in the world.

In my humble opinion - FRONT-BACK IS THE MOST IMPORTANT THING - either a good ratio in the antenna, or via shielding as well. I'm not sure if the RF Elements sectors will have enough F/B to be the best choice or not.

So - if you can only do 1' of separation and there's no possibiity to do more, or to add shielding - then it is what it is. :)  It may still work OK, but you're defeating some of the magic that Cambium's engineers put in there.  But, if you can get them to 30 dB of front/back issolation, I'd think you should be good. :)


I guess I should have been more specific in that I am using Cambium's sector antennas (Basically a purpose-built RF Elements antenna from my understanding) so I suppose I should be good in that regard. I understand the importance of GPS sync in any tower deployment, but we've yet to attempt frequency reuse with any of our micropop towers. My purpose in looking into it now would be taking advantage of frequency reuse to make 40MHz channels a little bit more economical spectrum-wise. We're operating mostly in rural areas, so I'm not too worried about outside interference currently. I guess it wouldn't hurt to give it a shot with the current mounting setup, but I'll still need to reorient our antennas a bit. (We've got a lot of older 4 sector installations oriented with overlapping coverage for situations with oversubscribed APs)

Back on the mounting setup though since I'd love to pry a little more space between the APs, I'm still wondering whether the bracket size of the Cambium sectors is close enough to UBNT's to utilize this or if there's anything similar that anyone around these parts have used? There's no measurements in the 'datasheet' and I haven't put my hands on a UBNT sector in more than a couple years. I'm not opposed to just purchasing one to check for myself, but I'm obviously more eager to see if anyone else has made an attempt. 

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we've used RF armors mounts on the cambium antenna, took a little adjustments but they fit and work well.   I've post photos in the story area with them on there. 

never hurts to have more distance between the panels, but the GPS is the magic bullet. just be sure you completely understand how to configure it, and how it works.   there are use cases that GPS doesn't stop all self intefence so be sure to take the time to tilt your sectors to fit your needs, forcase ahead if CPEs might hear two towers at a similar power and channel    with the good planning you can expect amazing results.