Mobile Emergency Communications: Mobile Repeater and Mesh Node.




Introduction: Mobile Emergency Communications: Mobile Repeater and Mesh Node.

What happens when the grid breaks? Communications need to be restored.

After Hurricane Katrina hit, BellSouth announced that it would take 3 months to restore phone lines. Volunteers using WiFi gear were able to connect churches and community centers within the first weeks and within three days of setting up an asterisk call server, routed 10,000 phone calls. Reliable backup infrastructure can be brought up in hours or minutes if you are prepared and have a plan in place.

Here is a plan for a mobile mesh repeater node to be used while you are setting up permanent installations, doing site surveys or for completely mobile teams.

Step 1: Make Sure You Have Everything.

Spool of Cat5e: I always use red to announce that there is power running through it.

Crimpers and Connectors: Even though it's wireless, you always need to use *some* wire.

Backpack or messenger bag: The orange bag pictured is a waterproof backpack/messenger that I got as a promotional item, Any durable, rubberized bag will do the job.

Power Source: I use a sealed lead acid Hawker Genesis 12V 16Ah. You can use any 12V battery, but it's important to pick something up with long life and low weight. Having an easy to find charging system is also a good idea.

Mesh Node: We are using the Metrix Mark II Kit here. Running Pyramid Linux, it can act as an access point, a client, a mesh node, and more. Being waterproof is also a nice touch.

Antennas: Whips are nice, but they don't go very far, For this setup, we've got an outdoor 8dbi omni and a small 10dbi patch antenna. This allows us to set up a directional link to our upstream node while serving clients locally. Picking your antennas really depends on how far you're going to advance and what you can carry. If you're using this as temporary infrastructure while setting up permanent installations or using it as site survey equipment, I recommend matching them with your standard kit. If you are only doing temporary sites, the above combination is pretty flexible. Both of these antennas were picked up at HyperLink

Step 2: The Wire

Because the Metrix Kit is powered over ethernet, this is amazingly simple.

Get a length of Cat5e (I usually use about two feet) and use a Cat5 stripping tool or sharp knife to cut the jacket right around the halfway mark. Slide the jacket off and cut it in thirds. Separate the orange and green pair from the blue and brown pair and slide the jacket pieces back on to make the cable tidy. Crimp connectors to the base of the Y as well as the orange and green side following this chart.

base of Y

orange/white | orange | green/white | blue | blue/white | green | brown/white |brown

orange/green pairs

orange/white | orange | green/white | empty | empty | green | empty | empty

On the brown/blue pairs, strip the individual jackets to expose the copper and twist together. You will be wrapping these around your battery posts.

Step 3: Make Sure It Powers Up.

Plug everything in before you screw the lid on. BLUE goes to RED on the battery, BROWN goes to BLACK.

Make sure the LEDs light up. If they don't, doublecheck your connections.

You may also want to configure your kit at this point.

Step 4: Plug Everything in and Put It in the Bag

You're pretty much done at this point. Toss a wifi phone in for testing and you're all set!



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    23 Discussions

    You have a good start. The biggest faults I can point out are endurance and survivability.

    A part of my job is developing and using rapid deployment networks for things like disasters. All too often your temporary setup becomes longer term as workers come to rely on it.

    There are three things that will improve your setup.  The first is the ability to power it in the field without any supporting infrastructure.  This is a particular favorite of mine for that application

    They're not that expensive and they'll manage the power for you.  It also provides a port to plug in and configure the radio locally if needed.  You will need to size your battery to run roughly for 24 hours without power.  If you add some good folding or rollable solar panels with enough output to charge during the day you have a reserve for cloudy days.  A small wind turbine is also handy.  The charging unit provides inputs for both.

    The second thing is to get rid of the bag and place it in a pelican case.  You can mount the radio board, charge controller, and battery all in the case and drill some and waterproof the ports for the antennas.  Their are waterproof connectors for charging and Ethernet as well.

    The last is a little extra protection for the electronics.  Things will leak, condensation will form, and you need to be prepared for it.  Two products we frequently use is Corrosion X and Boeshield T-9.  You can spray down the electronics with Corrosion X and it'll waterproof the boards.  It's non-conductive so make your connections before you treat the board.  The Boeshield we use primarily in cold environments where we expect ice to form.

    We use Routerboards and Ubiquiti a lot in our setups.  They're inexpensive and work well.  We have different setups for different situations but they're all simple and rugged in design.

    We stay away from mesh setups.  If you have mobile nodes it's applicable but most of the time our links are static and  the network is designed to be flexible and easy to deploy in the field.

    Good luck with the design!

    In said bag it would be simple to clip it to a flagpole line and hoist the whole thing up! use the long cat5 to run to the base of the pole (where the battery will remain safe and accessible.)

    For the battery you could use a charger from a trailer break-away fail safe system.One good one is the tap system and it recharges the battery and stops it from being over charged. Plus then you can add a 12v car adapter to it and recharge in the car.

    I am worried about safety aspects on this project.

    1) You didn't install any sort of protection for this device, I would highly recommend a voltage regulator to supply the unit with the correct amount of current and voltage. This will prevent spikes such as those that would occur from charging.

    2) Installation of inline fuses is a must for this type of project.

    3) How do you plan on charging the battery? This will probably run somewhere around 5 days depending on data usage with this size batter. Why not install a small solar collector as well?

    4) Antenna above AGL is a must for something along these lines to have good coverage. This type of packaging doesn't really support this. Why not a pole mountable box? Mount it to the side of a telephone pole, lamp post, set it on a tripod, etc...

    5) Finally, what is this talking back to? Most Mesh Nets require one or more WAN points. This Instructable does not state whether this is a node, router, or end user application.


    12 years ago

    This of course presumes that the WiFi internet connect will exist. Hardly a realististic emergency scenario, on two levels; the existance of the landlines (which weren't there after Katrina), and someone connected with an access point. Which definitely didn't exist. Nextel couldn't keep their trailer running for more than some six hours at a time, and the other wireless carriers didn't fare better. A great idea in concept, but lacking in view.

    2 replies

    indeed HAM Radio solutions usually fair better, this does of coarse mean that the general public is still without direct contact, during an intense such as this most telephone companies will activate emergency only traffic anyway. However, that being said if you could use some sort of satellite internet you might be able to arrange something, yes the latancy is horrible and most voip won't work (I know cause I am stuck between either sat or dial-up), but it is still better than nothing.


    12 years ago

    On review, for local comm, it is doable. Sorry for that. No edit, ya know..

    Has this been extensively tested? I have a few questions on the design. I tried a mix of patch and omni antennas using a WRT54 while trying to cover an 80 acre area using WDS and received problems with the diversity antenna logic. It would start dropping packets while listening to either the local or remote node. My current recommendation is that mixing directional and omni antennas without using multiple radios and backhaul channels will give you disappointing performance, dropped connections and low throughput. I think a lower cost, but less durable packaging, version of this can be created using WRT54GL based routers, they are in the 50-70$ range and you can then put something like dd-wrt on them. Take the cpu board out of the box and put it into a different enclosure if you want. The voip build even runs SipAtHome which makes the router an outbound proxy and treats all LAN voip phones as a "local" call, so you can have an internal phone network as an added plus, even when your external connection goes down. Use sipura ATAs and even get painless secure (SRTP) calls. rearden

    1 reply

    The Mark II uses two radios, not one, so you're safe from that particular problem. The WRT uses it's dual antennas (in diversity mode) much like you use your ears. It can hear with one, but it can hear better with two. Using a mix of antennas like you diid on your WRT will generally lead to heartache (as you found). It is true you can do some interesting things with the WRT54GL, and I have spent quite a bit of time hacking on the WRT series, but I've found that when building infrastructure that simply 'must work', you generally get what you pay for. WRTs do not operate over as wide a range of power, have intermittent problems, and are generally known as 'kind of flaky, but good for the price' by those who use them.

    I'm not involved with this project, but here are some guesses: 1) The antenna would allow users to pick up longer-range signals, by virtue of simply being bigger and badder. It probably connects to the box via a coaxial cable, similar or identical to your TV cable connection. 2) The box uses the PoE (or Power over Ethernet) standard. A lot of people don't know that you can power small devices over Ethernet cable, the same way your phone is powered by the phone line. He's taking the two power wires from an Ethernet cable, hooking 'em into a battery, and tying off or crimping off the rest (since he doesn't need the data connections). In theory, you could hook this into a solar panel as well, or rather you'd connect the battery to a solar panel, since you'd want the solar panel to charge the battery. This is a really interesting design; I'm potentially laying out a wide-area wireless network in a remote location, and this is ideal for my purposes. A modified version could serve as permanent access points, and I could carry it around with me to test it! Very cool.

    1 reply

    Originally, this was put together for just that. Doing sight surveys with a laptop and antenna is much different than doing a sight survey with the equipment you are going to use. By having the kit portable, you can determine if you can make the shot before you go through the time and expense of finding power or getting it installed (electricians aren't cheap).


    12 years ago

    Please have patience with us.......Yeah, I consider myself a pretty tech savy guy and thats why I love this site. But many of the projects are seriously lacking in good instructions or backgroug info. Sure I could spend my life searching google on things like this but when someone posts really good instructions you rarely have to. Im really interested in backup comms because I live right smack dab in the middle of eathquake central. I see that you split the cable and part of it went to the battery but where do the rest of the connections go? Also more detail on the antenna would be helpful. helter had an interesting comment about being able to do it for cheaper using spare parts.... tell us more please.

    1 reply

    Reply 12 years ago

    The antenna is an 8dbi omni from Hyperlinktech. It's good for a radius of about 1-2 miles with clean line of sight and another antenna on the other side (not just a wireless card). If you look at step 2, it has a text diagram of where the wires go on each connector, including if they're empty or not. You can build it cheaper, but as Helter also says, this is the 'off the shelf' configuration. Metrix Kits are affordable, tested and easy, but not the answer for everyone.


    12 years ago

    Sorry for the newb question but is the point of this thing so you can pick up wifi signals from farther away? Does the antenna mount to it in any special way?

    1 reply

    I'm with you... a bit of background for us tech peons please.


    12 years ago

    Nice, simple and effective mod. Have you thought of adding solar panels to charge the thing? P.S. I like the orange :)

    1 reply

    You'd need some big solar panels, plus, a charging circuit. It adds to the complexity and makes it that much harder to just throw together. Solar rigs are good for permanent installs in off-the-grid situations, but unfortunately they're not the best for quick-and-dirty setups. I like the orange too :)