Unstable Airport Express connection

Question

I have a problem of unstable connection to the Internet via Airport Express and Time Capsule. I have read a number of messages in the Discussions and learnt the signal-to-noise measurement. But, I still cannot resolve my own problem: the wireless connection of my iMac in my study room is unstable. Please help.
I have a 2TB Time Capsule in my bedroom. It connects to the Internet. I have two Airport Express (AX1 and AX2). I placed AX1 in my study room for my iMac. The bedroom and the study room are on the same floor. There is a concrete wall between them. I placed AX2 in the living room downstairs of the study room for my MacBook Pro.
I used Airport Utility 5.5 and found the signal-to-noise values as below:
Time Capsule has 2 clients.
AX1: Signal -78dBm. Noise -87dBm. Rate 2. Type 802.11b/g/n.
AX2: Signal -84. Noise -93. Rate 2. Type 802.11b/g/n.
AX1 has 2 clients:
Time Capsule: Signal -24. Noise -95. Rate 104. Type Wireless.
iMac: Signal -63. Noise -93. Rate 117. Type 802.11b/g/n.
AX2 has 3 clients:
Time Capsule: Signal -24. Noise -95. Rate 52. Type Wireless.
iPhone: Signal -24. Noise -95. Rate 1. Type 802.11b/g.
MacBook Pro: Signal -52. Noise -88. Rate 145. Type 802.11b/g/n.
Does it mean that AX1 and AX2 receive good signals from Time Capsule (-24-(-95)=71) but Time Capsule receives very poor or no signal from either AX1 or AX2 (-78-(-87)=9 or -84-(-93)=9)?
Airport Utility shows a chart of signal. The signals of iMac and MacBook Pro drop and rise frequently. It drops for 1 or 2 minutes and then rise for 10 or 15 seconds and then drops and rise again. What is the likely cause that drops the signal intermittently?
Finally, my intention is to use AX2 to connect to AX1 instead of Time Capsule. I want AX2 to further extend the network that AX1 has extended. But, it seems that AX2 connects to Time Capsule. I have set Time Capsule as "Create a wireless network" and both AX1 and AX2 as "Extend a wireless network". Is it a correct setting?
Please help!

Answer 1

The signal and noise values are useful, but what you need to look at is the signal to noise ratio:
Welcome to the discussion area!
Here is a chart of signal to noise values provided by Tesserax:
40dB = Excellent
25dB to 40 dB = Very good
15dB to 25 dB = Low
10dB to 15 dB = Very low
5dB to 10 dB = No usable signal
Your measurements indicate that both of your AirPort Express devices are positioned either too far away from the Time Capsule, or there are too many obstructions between the devices that are absorbing the signal strength. Can you try different positions for the AirPort Express to see if you can establish a better signal?
+Finally, my intention is to use AX2 to connect to AX1 instead of Time Capsule. I want AX2 to further extend the network that AX1 has extended.+
As you note, the AX devices both connect to the Time Capsule. Unfortunately, it is not possible to configure AX2 to connect to AX1 using the "extend" setup.
Think of the "extend" setup like a hub and spoke(s) of a wheel. The Time Capsule is the "hub" and the AX devices are at the ends of the spokes. The AX devices communicate only to the Time Capsule, not each other. Is it possible for you to reposition the Time Capsule in a more central location?