I have several older 3G and ADSL modems I was not using. I wanted to install a "repeater" to my guest house that's about 50 meters away from my primary ADSL Modem furnished by my ISP. Prior to the Utility Co. installing fibre optic cable and ADSL via my telephone line I had to rely on 3G service and a 3G USB modem/router, a TP Link MR3420. It is a modem/router both USB-3G and ADSL but because my ISP furnishes my primary modem I had placed the TP Link modem/router in a box had put it in storage.
Because I needed a Repeater to have a decent signal to my guest house I started in investigating Repeaters and actually bought a TP Link 701n that works great but I also needed a second repeater for another area. I contacted TP Link Forums and got a huge surprise, one of the members sent me a link to a "third party" firmware supplier called https://www.gargoyle-router.com/download.php. By flashing the firmware of my TP Link router it extended the basic modem/router ONLY into a "repeater" or whatever I wanted. It works perfect with the Gargoyle firmware as a repeater and not only saved me from buying a new repeater but let me use a "paperweight" I had stored for 2 years.