Extended Airport Express fluctuating data rate

Question

I have a 2012 Airport Express connected to my broadband router in the far corner of the ground floor of my house. The AX has provided faultless service, except for the fact that it's range drops off when I'm up one floor, on the diagonally opposite side of the house.
I bought an extra AX to extend the range of the first. It's set to wirelessly extend.
The problem I've got is that the data rate that the second connects to the first at keeps fluctuating, it can be as high as 144Mb/s, but also drops as low as 1Mb/s.
The RSSI is approx -76 dBm.
I assume that the two Expresses are re-negotiating to try to establish the most stable rate? However, with an average throughput from my ISP of 10Mbps, the low rate can really cause problems.
Can anyone suggest any other reason for the problem?
Thanks,
SPD.

Answer 1

Data links between a pair of express can be very tricky.
I find in my setup that I do need to restart the remote unit every couple of days.
But you need to take control of the system.. to make it as stable as you can. Apple have channels set to auto but also band swapping can take place.
Where you are in a situation where the system becomes unstable step in and take more control.
On the main Express plugged into the router. Set all new names.. short with no spaces and pure alphanumeric.
AX1 say for base name. (second one will be AX2.)
I recommend using different wireless names.. others will disagree but I find it helps.
So AX24ghz and AX5ghz (I am assuming your 2012 is the new gen2 AX)
Set fixed channels.. try 11 for 2.4ghz and 36 for 5ghz to start with.
With your upstairs AX2, you will then set to extend on say 5ghz band.. and give it a try.. see what the connection is like and if you get better transfer speeds.. if so stick with it.. 2.4ghz has better signal penetration but poorer speeds.. 5ghz can work poorly at a distance.. but in my double storey house I find from one end to the other, 5ghz is still faster and cleaner signal.. even though the signal level is lower.
If 5ghz doesn't work well then you will need to stick with 2.4ghz.
Some strange effects come out of all this.. but it is well worth a try.
I have noted when replying to this question.. several times.. that a v5 airport utility makes this easier as it shows more info.. link speed. Apple removed so much info in v6 utility to make your mac look like an ipad.. that it is a shame to call it a utility.. more like a toybox. So if you can possibly run v5 utility do so and you will then be able to track exactly link speeds.
This is my setup.. centre shows the main AP.. with the two each side extending the signal.