While I am an experienced Network engineer and work with wireless in a large fortune 100 office setting I am in the middle of doing my first outdoor WiFi installation and first Mikrotik installation and want to make sure I am on the right track so any comments/advice would be greatly appreciated.

Question 1: Assume I have a 500mw 2.4ghz 802.11b/g/n radio (say a RBGrooveA-52HPn running on 2.4GHZ) and the client is a 100mw security camera. Would it be correct (if a little over-simplified) to say that to ensure the AP can hear the client at approximately the same signal strength as the client hears the AP the client needs an antenna with 7-8db greater gain then the AP? I am thinking that because each 3db gain doubles the output power in order for the 100mw client to be broadcasting at the same power as the AP it needs that much more additional antenna gain.

Situation: I am trying to install a "goat-cam" at a barn. The purpose is to allow the farmer to monitor the maternity ward where the pregnant goats are without having to get up every two hours and trek in the middle of the night to the barn. The camera is an outdoor rated 1.3megapixel PTZ with both Ethernet and 2.4 GHZ wireless (rp-sma connector) available. The barn is about 300ft from the farmhouse and is a metal roof, wooden plank sided structure built late 1800's or early 1900's and the house is a 1780's fieldstone structure utterly impervious to WiFi. The saving grace is there is a porch with large overhangs that abuts the office area (where the internet connection is) and it will be relatively trivial to run direct-burial rated CAT6 cable from the office to one of the columns on the porch facing the barn. The issue is that the camera is in the middle of the "basement" level of the barn and the signal will need to go through one plank wooden wall, the floor and possibly be further blocked by the floor joists. My gut tells me that while there is an outside chance the Camera could hear the AP there is no chance the AP could hear the camera in place with its 100mw, 2db omni.

Question 2: Given the situation above, does the following solution sound "sane"? Is there some option I am missing or am I on the right track? Do the Mikrotik part numbers sound appropriate to the use?

I looked at a couple of options and the one I think is going to be most reliable and in the end maybe even cheapest is simply to use 2 Mikrotik RBGrooveA-52HPn with the included 6db omni antenna's on the 2.4Ghz band. The one on the farmhouse porch will be in AP mode and the other will be running as a client bridge installed on the barn wall facing the porch and connected back to the camera via the same grade direct-burial CAT6 I will use for the porch. I included CAT6 surge protectors at the farmhouse and camera ends, all CAT6 will be outdoor direct-burial rated with proper drip loops and surge protectors are installed for all power inputs. The inside of the barn is actually dry but pretty dusty and the camera location should be protected from the worst of the cold and heat.

I looked at trying to eliminate the second AP by putting a high-gain antenna on the outside barn wall and running antenna cable but by the time I bought the cable and a decent antenna I have equaled the cost of the bridge not even counting that I then need to account for 3db of loss from the antenna cable.

If you just want to link 2 places, use a pair of point-to-point devices and avoid omnidirectional antennas.
My guess is a pair of SXT Lite5 ($59 each), you can even install those devices under the roofs or behind walls (you'll have to test it before, of course)

If you just want to link 2 places, use a pair of point-to-point devices and avoid omnidirectional antennas.
My guess is a pair of SXT Lite5 ($59 each), you can even install those devices under the roofs or behind walls (you'll have to test it before, of course)

Wow, I can got SXT Lite2's for $40 on Amazon so those are winners! Thanks for the advice, those were perfect!

Maybe you'd like to rather use 5g instead 2g version.