29 thoughts on “Cat-5 Ethernet/Serial/PoE to your wireless router

  1. I thought of passing my own power through cat5 once. It would be nice if you had “tap-out” plugs, to where you could plug any old cat5 into them and it will move those 4 wires out for access.

  2. Personally though, I’m gonna leave the router inside, and run a COAX cable to the roof and “simply” replace the antenna of the router with a J-Pole antenna on the roof. Seems a lot simpler. Am I missing something ?!

  3. Now that I think about it, I’m not sure I’d want my power supply hooked directly to a twisted pair in cat5.

    …Now I just gotta connect these two wires….and POP, power supply shuts down from short. At least the fan is salvageable if it dies.

  4. The motivation for getting the device as close to the antenna as possible is signal loss in the cable. At 2.4 GHz coax cable is *very* lossy. For example, good RG-58 cable has a loss of 18.3 dB per 100 feet at those frequencies. In only a 16 foot run you’ll lose 3 dB, which is half your signal. It’s even worse for thinner types of coax, like RG-174.

    This isn’t a problem you can solve with more shielding; it has to do with the foam dielectric between the inner core and the outer shield, which becomes lossier with higher frequencies. The only way around this, besides using very short cable runs, is to use waveguides, which are very unwieldy — hooking them up is more like plumbing than wiring.

    When constructing an outdoor enclosure you need to think about condensation as well as water intrusion from rain. In commercial enclosures the usual practice is to either include a small “breather” hole on the underside and include a heat source to drive out moisture, or place a packet of silica gel inside the enclosure before sealing it to dry the atmosphere inside.

  5. Is the inclusion of the TV tuner in the diagram relevant to the project at all?

    I’ve been far a use of the last 2 pairs… Though, if all your using it for is sniffing Wifi, why bother with serial, just use ssh!

  6. @atrain

    In early project planning, the idea was to use the fourth pair to send the audio and video from the camera on the roof through the cable to the desktop computer. (Who doesn’t want a video camera on the roof?) When I realized that a serial cable is much more important, I swapped out for a wireless camera, and used the fourth pair for console. The wireless camera leeches power from the router, and needs a wireless receiver.

    The reason the serial console is important, is the ethernet connection is not always available. For instance, during boot time, and when reconfiguring the interfaces. Nothing more secure than a hardline ;)

  7. seriously ghetto (my fave was the silica pack in the router rofl) but *l’esprit de hacker* is worthy of an approving nod

    my improvements would be:

    - weatherproof enclosure; many avail for WRTs
    - tap out the PoE and Serial neatly in the enclosure
    - use a simple 2-port RJ-45 box to breakout on the far end; use the Cisco-style pinouts and a decent cable
    - high gain antennas of course

  8. Since Steve is on here, I’ll just post this on here.

    You’re not taking the cable resistance into mind when powering it or putting serial data on it. At 100 feet, the cable should have a resistance of 5.16 ohms per conductor, so 10.32 ohms per V+/Gnd and TX/RX. If, on power, the router is pulling 1amp, you are dropping 10v, so only 2v would get to the router. I’m assuming its .5a or .25a, so dropping 5.16 or 2.58v, so you get 7v or 9.5v at the router. For the serial port, what power/logic levels is it running at? 5v? I doubt it’s 12v. How much current is the router sinking for data?

    Grab another 100 foot cable, add a 14ohm resistor to one end, and then 12v to the other end. It should pull .5 amps and measure 7 volts at the resistor. Adjust accordingly.

  9. You need at least LMR 400 or 600 to run so you have little loss, but hardline is better. Now the cheap man’s alternative is to use RG 6/U double shield, but it is 75 ohm coax, so you’ll need an antenna analyzer to properly tune your antenna so you have a 50 ohm impedance at the radio.

    I use Celwave 3/8″ hardline for my rooftop wifi. It’s affordable for less than a dollar a foot. Connectors are $20 a piece though. This runs to a high gain vertical, and I can reach out even further using my commercial equipment I have on the tower.

    The best thing to do though is get yourself an amateur radio license, then you can get into the good equipment that you can put some power behind.

    (The technician license should be a no brainer for anyone reading this site.)

  10. @cde

    I thought it would be an issue as well, but the WRT54G series has an excellent onboard voltage regulator. It can handle pretty much anything between 6 and 18 volts. I haven’t measured the amperage very accurately, but it’s running from my desktop’s PSU with no trouble at all.

  11. Andrew : Haha, yeah I was wondering if someone would mention that. I did the math, and the radiator part of the j-pole (the longest part) would only need to be 8.8cm long and the driven stud 2.95cm. :) You could make it out of clothes hangers ! :) (There’s a ton of options for antenna’s, I’m just a fan of the J-Pole since it’s relatively easy to make for any frequency and has some DB gain to it.

  12. WARNING! This is NOT REAL PoE, this is a dangerous ‘hack’ and in no way compatable with standard PoE.

    PoE standard is much more complicated and uses sensing protocols to determine if a device is PoE compliant before initiating a 48v feed from the PoE controller.

    In short, although this may work with your own hacked kit, DO NOT UNDER ANY CIRCUMSTANCE plug either your powered device or powered network cable into anything other than your own hacked devices.

    However, it’s a free world…. so try what you like!


  13. You’re right Adam. Also, if you don’t already have the knowledge, going for your general or extra will give you more insight into feedline/antenna issues, although antenna design is normally more of a black magic. Most omni stock antennas I have seen are a dipole or co-linear, with the same or better performance than a j-pole. The active portion of a Jpole will be only about 3-4 inches tall.

  14. I’ve spent a lot of time messing around with PoE at work for a commercial application.

    If I understand Steve’s diagram right, he’s simply sticking a voltage onto the spare pairs?

    I’m not going to tell Steve he’s in any way wrong to do that, but I would strongly recommend to anyone looking into implimenting PoE for any reason (homebrew or otherwise) to NOT do this. If you’re at all interested in using PoE, go google for 802.3af where a really quite standard has been laid out. Then, go purchase some magnetic modular RJ45 jacks for a very small cost and swap them into whatever device you need to PoE enable. The 802.3af standard has numerous failsafes designed into it, when you look at them it really is a no brainer. The various jacks have centre-tapped transformers with series and shunt chokes to filter common mode interference. It’s perhaps a few bucks of gear and a lot less work.

    I would also recommend injecting at 48V and using something like DC-DC convertors or even just a potential divide to get the voltage levels you require at the other end. For more than a few meters of cat5 it’s just common sense to do so. When running 48V you can get the full potential of 15W out of your 4 ‘spare ‘lines (there are also draft standards for about 56W but you’re looking at phantom power techniques here)

    Good luck.

  15. Just wondering, if I do this, and plug the other end into computer with the 12 volts (or 48, whatever) will the device not be fried?

    Like if someone unknowingly used a poe wire to plug in a laptop on the roof to diagnose something.

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