Home router recommendations

Hey there, i'm looking to buy a new router that can have something like dd-wrt installed with no hardware-backdoor shenanigans on it. Also, does having multiple antennas and 5Ghz connectivity have any effect on Wifi coverage? All the walls in my apartment are made of compressed concrete and steel framework which severely affects the quality of the signal.

Multiple radios will help with coverage and throughput, but 5ghz struggles a lot more with walls than 2.4ghz does. So you'd expect less range and a weaker signal using 5ghz, but the extra bandwidth might make up for it.

Compressed concrete is going to be a bitch even with 2.5 GHz wifi, that shit will ruin your signal. 5 Ghz will struggle to get through the walls, but most 5Ghz systems are also 2.4 GHz capable, and you can broadcast two SSIDs, one on each frequency band. I m not sure how much cash you have to spend, but the Linksys WRT-54GL is dd-wrt compatible, and isn't terribly expensive. http://www.linksys.com/us/p/P-WRT54GL/

The nicer Linksys WRT models don't have DD-WRT support, but the are designed to run OpenWRT, which is a nice alternative.

Multiple radios, as @Dexter_Kane said above, can help with coverage, but depending on the size of your apartment, it won't be super critical to have a ton of them. The biggest issue in the walls there, since compressed concrete is fairly unkind to most signals. The metal framing may or may not be an issue, it depends on what kind of metal it is, and potentially how it's shaped. Maybe the builders accidentally made a faraday cage out of the place. I doubt it, but it would be cool.

It's a standard commie-era building, framework for each panel is a steel cage of sorts, making up a grid. The radius for all devices that will use the router isn't going to be much further than 5-6 meters, but the concrete limits that severely. The signal that actually gets through is mostly the one which bounces off the walls and through the doors. I wouldn't say its a faraday cage (you'd need a finer mesh for that) but it's enough to make for an annoying wifi experience :)

Weren't Linksys routers infamous for having nasty NSA backdoors in them? I was hoping that someone with more knowledge on the subject could shed some light on that.

Linksys shouldn't be any worse for NSA stuff then any other it was Cisco that is infamous. Any dual band router supporting the 802.11ac standard will have the 5ghz band and the 2.4ghz band should deal poorly with that condition. Sadly no fast wireless standard deals well with metal or reinforced dense concrete. You could look to Tri band Router they are more expensive but promise better performance in conditions such as yours. While I don't think any normal consumer router will perform great so long as you aren't trying to receive signal 2000ft away I think the more powerful dual and tri bands should perform. Netgear and Asus have some good options. I can't speak on what kind of software they run but I assume the Netgear is locked down, and the Asus takes some work to force into doing extra things.
Having longer and more Antennas should in theory extend the effective range of said unit but, these days I think it is merely aesthetic.

The WRT-54GL only supports up to wireless G. The range it gets is pretty phenomenal though for a decade old router. I can access my wifi almost 1000 feet from my house while at my neighbor's house. It's not dual band though, and if you have anything better than DSL or a crappy cable package, it'll bottleneck the connection. All in all it's not bad for a router I picked up for $40.

Hm, what about using an external signal booster? That should work with just about any router, right?

Grab a few POE adapters instead of relying on wifi.

Yeah, I only recommend it because he specifically wanted DD-WRT. I would personally buy one of the newer Linksys routers and flash OpenWRT to it. I know a few guys who use Rukus or Ubiquiti devices in their homes, but none of those support DD-WRT AFAIK

I settled for the Asus RT-N18U. It's designed to be compatible with open-source firmware and the microcontroller is an ARM Cortex A9 with a huge amount of flash (128MB) and RAM (256MB). It also has a USB3.0 port so i can use it as a tiny NAS. Wifi signal strength is still poor, but it's stable and reaches over 20megabit on speedtest.net even in the worst places of the apartment.