Is it possible to extend the antenna for wireless router over coax?

My house has a smart box, and all cables (coax and cat6) in the house run to it. The box is on the second floor in a closet in the far corner (furthest location from my office). I keep my modem and WiFi router on a shelf next to it. That way I am able to easily plug in all rooms into the router.

The unfortunate effect is that the WiFi signal doesn't have that great of a reach to the other side of my house. My router has 3 antenna on it, and all coax cables are being unused in my house. Is it possible to connect a coax cable to my router and then attach the antenna to the other end in another room effectively giving me an "extension" cord of sorts to the location of one of the antenna?

I guess there are two(three?) questions here:

1. Do adapter exists that will let you connect a coax cable to a wireless router's antenna connector? I will need similar connector to let me screw the antenna into the other end of the cable.
   • What is that connector even called?
2. Will the signal carry OK?

Solution 1:

Your proposal won't work, for several reasons:

1. Wi-Fi products use 50Ω coax for their antenna cables, whereas home CATV/TV antenna coax cable is 75Ω (RG-6, RG-59). So you'd have an impedance mismatch unless you put impedance converters at both ends.
2. Wi-Fi uses 2.4GHz and 5GHz frequencies, and requires coax cable designed for low signal loss per unit of length at those frequencies (usually rated as deciBels of loss per 100ft in the US or deciBels of loss per 100m in the sane world). Home CATV/antenna coax is usually only designed to be good for traditional broadcast TV or CATV frequencies, which rarely go above 1GHz, unless your home was (re)wired for digital satellite TV service, in which case you may have cable rated for frequencies up into the 2GHz range. Typical loss per 100ft for RG-6 coax is something like 13 dB, which means a 100ft run would cut your signal down to less than one-quarter the power.
3. The extra antennas are 802.11n and 802.11ac gear are usually hooked up to separate radio chains of a MIMO radio, which means they're designed to work together as a kind of small antenna array. Moving one antenna far away from the rest is likely to break their ability to work together properly.

Instead, you should make use of that Cat6 cable you say you have, and run Ethernet to another Wi-Fi AP. If that's not an option, you might look into using MoCA (or G.Hn/HomePNA over coax) to send data over CATV coax at Ethernet-like speeds. Last, there's HomePlug AV2 MIMO and G.Hn over powerline.

Solution 2:

Short answer is No.

I'm assuming the coax you are talking about is for a Cable service.

The characteristics of that coax are likely not compatible with the characteristics your router is designed for. Even if they are, and in perfect condition, the loss over the run you describe is likely to be to much for the router to overcome.

As noted previously, a second access point with a wired connection is a much better solution.

Finally, I would consider a repeater, or range extender, a last resort. At a minimum, you will reduce your theoretical maximum bandwidth by half as each packet has to be sent twice using the same resource. (If you use more than one repeater, it is half of the remainder lost each time.)

Solution 3:

Yes, there are adapters for converting between impedance at minimal loss, and yes, the signal carries fine over RG6 cable. You can DIY or use a Coaxifi kit, which includes adapters for 75 Ohm F and 50 Ohm SMA + RPSMA connectors. The Coaxifi splitters have a stated range of 2400-5875 MHz. The signal should be as strong over a 25 foot cable run as it would be over wireless alone at 5 feet from the router - which makes sense, given the radiation pattern of your average router antenna and how it wastes the output wattage in every direction. You could combine two radio chains from the router for extra output power behind the splitter. This approach might not make the best usage of MIMO if only one antenna port is used, but it does let you distribute antennas throughout the house, and lets you roam seamlessly from one antenna to the next at full bandwidth without any extra processing necessary.

Keep in mind that at 5.8 GHz, if your RSSI is -25 dBm at 0 feet from the router's antenna and -48 dBm at 5 feet away, the -48 dBm reading reflects a loss of all but 0.5% of the original output wattage. (Most of the other 99.5% radiates out around the dipole in a tall donut pattern.) For real time applications, you should be fine down to -65 dBm RSSI, which is about 0.01% of the original output power in this example. You can use Times Microwave's calculators to check run efficiency for various cabling lengths and types. It looks like you could stay above -65 dBm out to about 120 feet on a single RG-6 run, and considerably farther using LMR cable. So unless you're extending Wi-Fi for the whole length of Wayne County Airport on a single cable run, Wi-Fi over coax should work for any run length in your home.

You can read the Wi-Fi over Coax Wikipedia page for more details.