Two Omnis, vertical and horizontal separation requirements


I have a tower with an ePMP2000 AP and 5 GHz Omni and need to increase capacity. The tower is very light and cannot support sectors, but can support a second AP and Omni.

Obviously will be using GPS sync and will NOT be reusing frequencies. My question is, can I install both at the same vertical height, or do I need to have them vertically separated? My thought is that they can be at the same vertical height since they will be GPS synced and that the dynamic in-band filtering of the ePMP 2000 would work well as long as I choose channels are far apart as possible, but I wanted to inquire in case anyone has done this before and can give me advice.



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If there is a definitive answer to this I wouldn’t mind knowing it.

From way back in the day I remember the rule of thumb being the length of the antenna. If it was a 10ft Omni then they needed 10ft of separation. But I know I also remember it being 1/2 a wavelength, 1 full wavelength and three wavelengths depending on who and where you ask.

I had asked once why it was that home wifi router’s antennas were obviously not one antenna length or wavelength apart and it was explained to me that the distance you want to reach is also relevant while someone else said it was the gain of the antenna that mattered… however no one could explain how either worked into how far apart they needed to be.

Somewhere I remember seeing someone on a forum somewhere post a rather complex mathematical formula for figuring it out but I’ve long forgot/lost it and don’t know that it was even correct.

Someone at KPP once told me the KPP sector I was asking about needed 4ft of horizontal or 10ft vertical separation due to the way the side lobes were… so maybe some antennas need to be farther apart than others.

I was also told once it didn’t matter as long as there was 20Mhz separation between the channels. And I believe KPP told me that a Dual 5Ghz sector I was asking about required 20Mhz channel separation to work correctly. So those are basically 2 5Ghz sectors right on top of each other in the same radome.

From personal experience almost all of our antennas are on water towers and many of them are stand pipe water tanks with an 8ft diameter so no V separation and very little H. On two we have to mount our antennas to the ladder rail where it comes over the top of the tank. In these cases vertical separation is impossible and horizontal separation is about 2ft and I’ve never noticed them behaving any different than Omni’s on other towers with 4ft or more separation (mostly kpp and ubiquiti 5ghz omnis).

Hello Sir,

if you want to increase capacity and range, obviously you need sector antenna, capacity comes when you have a better received signal at the client side and AP side and better Signal to Noise Ratio (SNR). This is achieved by more gain between the communicating antennas.
So, adding an AP with Omni antenna might not increase considerably the capacity. Reinforce your tower and have ePMP 2000 AP with 120 degrees and Smart antenna if you want more range and capacity.

Sincerely yours,

Niragira Olympe

for OMNI antennas: they must be vertically separated and if possible be not a multiple of the wave length. considering that these radios are in the 6cm band (12cm for 2.4ghz) make sure you are at least 9cm apart vertically. We use 28" (71cm) and choose channels that are far apart (at least one channel width, so if using 20Mhz channels pick channels 60Mhz apart if we have to stack an omni’s (usually waiting on sector panels but need the SM capacity).
DO NOT place omni antennas at the same level as the RF from one antenna can/will saturate the other. This happens even in synced systems.

If you are needing range/better SNR then I would suggest strengthening/ supporting (add guy wires) your tower to carry the wind load of sector panels. Just make sure you mount them so that you can’t physically touch two opposing antennas at once (rear spacing antennas in the back null), we generally us 3ft (1m) standoff and find we have less issues with offside chatter from out of sector SM’s.