Router

You can review this:

https://www.netgear.com/home/wifi/range-extenders/listing-filter/abn-wifi4/

 

Might be time to update your main host router though as it's EOL. 

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PatBri wrote:

which netgear router extender is compatible with the Netgear WGR614v9 router

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Depends on what you want to do.

 

Two routers on a network can be a recipe for chaos.

 

As FURRYe38 says, your WGR614v9 is ancient, with its V1 origins back in 2003. V9 was in 2007.