Issue Airport TC and Airport Express wifi

Question

Hello,
Any help much appreciated for this configuration that doesn't work:
I have the following conf connected via cable:
ISP modem --> NetGear Router FVS338  --> Airport TC + Airport Express () + NAS (qnap)
The Airport TC is plugged via the WAN port and works has a HD backup.
The Airport Express is plugged via the WAN port and works has primary wifi network (bridge mode + create a wifi network)
Both have automatic DHCP
Both have the Bridge mode ON.
I want to expend my wifi network by:
-  turning ON the Aiport TC's wifi (expend the actual wifi network)
-  setting up the exact same SSID name + same password as the Airport express.
Once i have done this i completely lose my internet connection, as if turning ON the wifi on the TC was messing with all the configuration.
Once i have turn OFF the wifi, everything goes back to normal !!!!!!
I have than try to connect both the AirPort TC and the AirPort Express via the LAN port, but it doesn't solve my issue.
Once the wifi in ON (on the AirPort TC) i lose my internet connection!!!!
Has anyone got the same issue?
What do i do wrong?
Many thanks for your help

Answer 1

I created a New Network on both the Airport with the same SSID and same password:
It seems to work perfectly.
My LAN network works fine and i can connect via wifi in my house.
Do you think that could solve my issue? Or it is better to have one airport in "Create a Network" and the other Airport (express) in Extend network mode?
Do you think the 2 wifi network (same SSID) can scramble each other?
This is far superior method.. known as roaming. It is where I would have suggested you go.
The extend wireless is only for situation where you cannot run ethernet. It is much poorer.
The 2 wifi networks are fine ..  in most cases. They have same name and same security but they should have one difference and that is wireless channels. With both set on auto they simply should sort themselves into using sufficiently different channels to not have a problem (or the distance is so great they literally cannot see each other).
A very good idea to use Apple's wireless diagnostics btw so you can see what channels everything is on.
It is available in Lion (though hidden) and was readily available from Mountain Lion on.
About Wireless Diagnostics
There is a lot more tools if you open the utility.
You can see at a glance all the different AP's in your area by doing a scan and can track performance of what you connect you as well.
I forgot to tell you that i have few Sonos devices (Play1, ...) plugged into my network.
Do you know that system?
Have you ever heard about any issues related to compatibility between Apple Airports and Sonos devices?
Sonos stuff can have issues. I don't use it but some people have posted their problems.. If you run into problems then just post the details.. I would recommend as much detail as possible in a new thread with Sonos in the title.
The new apple routers must be on latest firmware. If you have earlier products then firmware is a problem. It depends. Latest in that case is not always greatest. The particular problem was spanning tree protocol, which is essential to the Sonos but Apple messed up. (since their own products didn't use it).
You can simply do a search here (wireless forum area) for sonos.
here is typical one I handled earlier.
Re: Sonos, Time Capsule and volume permissions
The other thing mentioned in the thread there is Sonos is very much a windows network device.. odd when it is so Apple iTunes orientated. Please do not use Apple type names.. for anything. Use all network names that are short, no spaces and pure alphanumeric. That gets you around most of the problems that Sonos support cannot figure out.