Hello,

I'm looking for wifi devices (preferably usb-wifi adapters) with separate TX and RX. I came across MIMO and antenna diversity which seems to be related to this. Though there seem to be not that much devices which support this (mostly routers). I was also wondering when a router has multiple antennas does this automatically mean that some of them are for TX and some of them are for RX only?
For 100base TX ethernet there is also the auto mdix feature which can change what wire pairs are transmitting/receiving. Does a similar feature exist for routers with e.g. antenna diversity so that the chain with the sending antenna can also receive data? 
For my project (secure airgap) I do not want this feature.
However, if it does exist and is always implemented I would be interested in other possible ways to make a wifi device TX or RX only (from the hardware side!). The chips I came across use the same pins for transmitting and receiving and everything important seems to be incorporated into the chip so this is maybe hard to accomplish. But there may be other chips/devices where this is not the case and someone here knows them.

(Last edited by Jim79 on 3 Mar 2016, 19:59)

I don't think Wi-Fi works the way you think it works.

There is a negotiation before two devices before they can start exchanging ethernet frames. Once they are associated, before sending, a device has to listen and confirm no one else is transmitting. After receiving, a device has send an ACK, otherwise, the sender will retransmit.

All this activity is hidden away at a very low level. I think, but I'm not sure, that a lot of this behavior is controlled within various "black boxes" of either hardware, firmware, or binary blobs.

Of course this is not the way how wifi is normally used. But it is in general possible (from the software side) see e.g. here: https://befinitiv.wordpress.com/2015/01 … a-for-fpv/
At the moment my problem is merely hardware based.

Interesting hack...

Dual-chain 802.11n devices (ie N300+ routers and adapters) are common place. At least some of them support configuration of both sending and receiving antennas under linux.

"iw phy phy0 set antenna <bitmap> | all <txbitmap> <rxbitmap> ;# set allowed antennas"

As to the current state of support of this feature for various wireless chipsets, I have no idea. Maybe someone else can step in.