Has anyone tried a similar abomination? The main node I use has a 2dBi antenna. A 5dBi antenna performs worse for connecting to most of the nodes in my vicinity. It does however connect to some nodes further away. So I decided to try adding a separate 5dBi node. That way devices close by could choose to route via either node, whichever seems better. Or traffic could jump between the two taking local traffic from the 2dBi node and beaming it further via the 5dBi node at the expense of an extra hop. Thoughts, experiences?
Harmonic frequencies are more likely to be an issue.
If you have an antenna transmitting at 2.4ghz, you will also see subharmonic bumps at 1.2ghz, 800mhz, etc. A receiver at 800mhz could potentially get "washed out", or overpowered, by a 2.4ghz transmitter that is too close simply because of subharmonics.
Transmitters aren't perfect either. While you can get really strong transmissions at very specific frequencies that can propagate really far, electronics resonate at many frequencies and that resonance will make it to a TX antenna as noise.
Unless the antennas are designed to work together, you shouldn't put them that close together. (I am also speculating that in extreme cases, a weird configuration like that could detune the transmitter antenna in a such a way that it would blow out the transmission circuit. I dunno about that though.)