Review: USB over RJ45 for file transfers, KVM and more: 4/5 stars

If your home was built in the last two decades, chances are you have some Cat5 or Cat5e cabling in the walls. But you might not realize it, since the builder may have crimped it for termination at a 6P4C phone jack (RJ11). Re-crimping the ends for Ethernet (RJ45) is a neat little project, and while having Ethernet cabling to wall plates is great on its own, it also opens the metaphorical door to some other neat possibilities.

Cat5e cable originally in phone punch-down block, re-crimped for Ethernet

The Problem

In my home, I sometimes move office gear from floor to floor. Our formal 'study' smells funny, but there's still a printer in there, and sometimes an external hard drive, smartphone, and so on. Other times, I might need to connect a keyboard and monitor from a desktop in the basement to a more salubrious work environment. Ethernet's fine for PCs, and naturally supports higher data rates than powerline adapters do, but doesn't help much with peripherals.

The Solution

In cases like these, I use USB over RJ45 adapters. Basically, these make use of the RJ45 pin-out to send USB modulated data and voltage over Cat5e cabling. The steps are pretty straightforward, once you've got your Cat5e cabling crimped for 8P8C RJ45 connectors. Connect the male USB end to the source device (a PC in this case), and connect its RJ45 end to the cabling home run for a particular room. In that other room, connect an Ethernet cable between the wall plate and the other adapter, with the female USB end connecting to your peripheral.

Connecting a Cat5e cable between a PC and a keyboard on different floors

The Result

So far, I've connected external hard drives, a printer, and a Galaxy S5 this way. The best part is that the Galaxy S5 can actually be charged over Cat5e with these adapters, so you could use an Ethernet wall plate in case you run out of electrical outlets in a given corner. With a keyboard, the USB over RJ45 connection has been somewhat hit or miss at times, especially between BIOS and Windows boot, but that has more to do with the motherboard and Windows' driver support than anything else.

There are usually some cheap adapters for sale on AliExpress. You can also find a set where one adapter has 4 USB female ends, which could be useful for backhauling your entire home office from one room to another, or spare you the cost of buying a USB hub.

A set with 4 USB outputs on the same Cat5e cable!

Given enough room behind the wall, you could potentially stick a 4-banger behind a 4 port USB wall plate. I'd recommend using USB keystone inserts to make your own wall plate, though, since most of the 4 port wall plates on the market are for charging only.

Haven't tried this yet, but looks promising

Another thing you can do with Cat5e is HDMI over RJ45. Some KVM extenders include support for HDMI (VGA is often much cheaper), two USB ports, and infrared for a remote control. 

KVM & IR over Cat5e extenders

I've tried these and see lots of tiny red dots snow across the screen (maybe the TMDS impedance gets mixed up) even on very short Cat5e lengths, but to be fair, getting HDMI to display a perfect screen image over 50 feet of native HDMI cable isn't always going to work, either. If you have a particular model you recommend for delivering 1080p or 4K without noise, let me know. In any case, using a remote KVM setup this way can save resources on the machine being connected when compared with RDP.