Hello
i was planning to put one 2.4Ghz and one 5.8Ghz omni on a mast and just wanted to know does it matter which one should be installed on top and which one bellow the other
In theory no matter who is above and who is below.
In practice I would suggest that 5.8 ghz antenna to be placed on top.
Of course this is also depending on their radiation in the vertical plane and each antenna gain,
When using omni antennas the clients should be in the same height like Ap with omni antenna. So, place them according that taking into account their vertical radiation angle.