@Kevin_Z the datasheet only specifies it has 4 omni antenna, not which one is which. I need to know, preferably not through experimentation, which is the 2.4/top, 2.4/bottom, 5/top, 5/bottom.

  @ahutton 

Some websites have pictures that show the inside of this router. This could give you some clues about the antenna layout.

For example

https://fccid.io/TE7C80     -> download the "Internal Photos" PDF document. 

https://wikidevi.wi-cat.ru/TP-LINK_Archer_C80     -> copy or save the picture that shows the internals and you will get a hi-res image

So, when looking at the C80 router from the front side and counting the antennas from left to right:

1st antenna duct contains one 2.4 GHz antenna

2nd antenna duct contains one 5 GHz antenna

3rd antenna duct contains one 2.4 GHz antenna and one 5 GHz antenna stacked on top of each other

4th antenna duct contains one antenna that is apparently tuned to work for both 2.4 GHz and 5 GHz

My guess is that all antennas are of the sleeve dipole type.

It's interesting that one antenna appears to be a shared one. This should mean that this router can do 3×3 MIMO either on the 2.4 GHz band or the 5 GHz band, but not simultanously on both bands.

  @woozle thanks, that is useful.. it also means I probably shouldn't use the C80 to do what I was going to do and stick with one with 2x2MIMO as my external panels are two inputs on each.