Mesh Networks, Digital Radio, EMP, and Metal Buildings, Oh My!, by R.V.


We are working on a grass roots Internet style network at my radio club. As I am a very curious fellow, I am currently reading Wireless Networking in the Developing World, which is a free ebook. This book, of which I am 1/3 of the way through reading, seems to exercise every possibility in connecting these wireless routers. The pros and cons of various management strategies and switching tactics are exhaustively discussed. Sources and software are named, making it a great reference. What got me started is the Ham Radio version of this, which is described online, which is a project of my ARRL club. My interest was aroused by a presentation on digital radio at a club meeting.

Interestingly enough government emergency management money is being allocated to replace repeaters in Georgia with DSTAR units, which are the ICOM version of digital radio and the one that was adopted by emergency management people in Georgia. I understand that there are two other standards out there from Motorola and Yaesu, depending on the choice of the local emergency people. The three are mutually exclusive, meaning none will communicate with the other. A marginal upside to this is that you might adopt one of the other two and have a mostly private network.

I am nothing if not independent, and the feature of Amateur Radio that is most appealing is that it facilitates independent communication. Unfortunately, DSTAR gives radio a firm link to the Internet and throws cold water on the independent communication feature. While it may be really cool to talk to Idaho on your 2 meter HT via a repeater at each end and the Internet in between, what if that leads people to never explore 80 meter so you can hear the news from the Redoubt no matter what? That’s not a question I can answer. Rest assured that I will figure out that 80 meter thing. My main problem is a Yaesu appetite with a Baufang budget.

The crux of what is up is a member of our radio club, who dreams antenna configurations in his sleep and does not round the speed of light in his calculations, is working on flashing particular Linksys routers to change how they operate so they will seek out similarly flashed (meaning the programming or firmware is permanently changed on the chip) wireless routers with higher gain antennas than are normally found on wireless routers. My antenna obsessed club member has not shown me how to flash these units yet. (For the uninitiated, all Hams are antenna obsessed.) We are waiting on an opening in my schedule. Unfortunately the flashing I learned in college has little or no application, being the medium for the last thing you have to communicate to someone followed by a hasty exit.

What is interesting about the antenna is they are both directional and omnidirectional, depending on the application. Examples of off the shelf models can be found on eBay. My Ham friend is, of course, making his own.

So, we are working on establishing an independent Internet in a two or three county area with multiple paths for data flow and may even reach Atlanta. Any Ham with a ridge top house or business location is quickly victimized, since we are trying to establish the main spine, so to speak, of the installation. What is one more antenna sticking out of a tree or your chimney top, right? The ones we are using are about 18” long and contained in a ¾” PVC pipe with a cap. An old frying pan from good will or the sheet metal on your chimney serves as a ground plane. My wife will never miss that pan nor notice the added protuberance on the roof, surely.

The Linksys WRT54G routers with model numbers 1 through 4 and maybe 5 have more processing capability and memory than was necessary for the advertised task they were intended to carry out. A unit can be obtained for $10 to $30 at Good Will or a similar institution. A description of the reflashing process can be found at where they go through the hazards and the steps to accomplish the task. I found the term “bricking your router” amusing but hope I miss the first hand experience.

All this equipment is low power running on 12 volts DC. House power and a battery back up from the office supply can handle the day to day operation. Be sure to get one that has 12 volts of battery in it. If push comes to EMP shove, you can bypass the transformers that go from 120 vac to 12 vdc and back. A 20 to 100 watt solar panel, low end solar charge controller can be kept in a metal cabinet with an identical backup router for later that completes the set up.

When selecting a solar panel, the key feature is a “bypass diode”. Without that, anything that shields a spot on the panel makes that part of the panel perform like a resistor. Resistors have lower voltage. Silicon cells are supposed to produce voltage. Pretty quick, your efficiency is destroyed by random shading without the bypass diode feature. Of course, I learned that after making a purchase or two. Ready, fire, aim! All the major lessons of life are seared into your memory by shame, grief, pain, or all of the above.

My thought is that we can attach a camera here and a camera there and monitor the progress of traffic, wheeled or otherwise on major thoroughfares in addition to exchanging data. The inexpensive infrared technology featured previously on SurvivalBlog, for which you are loudly wishing for an article, potentially has application. I too am wishing for that article. Having notice of any sort, regarding the movement of the Golden Hoard as you call it, would be advantageous.

What is fascinating about this radio wave stuff is that every point along the wave is a potential source point. So, if you envision the rock in the water and the resulting concentric circles of wave energy radiating, you have the beginning of the picture. At the point where those circles hit an impenetrable object but for a pin hole, the waves stop across the plane but radiate out from the pinhole in the same concentric circles but at a lower intensity. This phenomenon is how you get signals around corners. Every point along the wave acts like a pin hole. It is also why metal buildings make lousy Faraday enclosures.

I have listened to all the fussing and complaining from tenants I can stand about the roof of my building. I have sent any number of people onto the roof of this industrial building to stop the leaks. It is empty now, so I have decided to bang around peeling layer upon layer of caulk and coaxing security screws out of various spots to figure out what might be the problem. It turns out that the initial installer of the roof failed to remove the wax paper backing from the mastic tape before the next roof panel was settled into place and screwed down. Typical of industrial buildings, the pitch is only 1 in 12. Most any heavy rain makes it leak in its current configuration.

The point is, every component of that building is sealed against the intrusion of water or soon will be using caulk or rubber in one form or another. Every screw has a rubber washer, and every thread has caulk applied or should. Each panel is mostly insulated from the other. The exterior of a metal building does not form a continuous barrier to electromagnetic radiation yielding numerous point sources. Evidence of this is in the observation of certain electrolytic processes, indicating that static electricity is traveling down the gutter brackets, gutter, and down spout to the ground and not through the frame of the building. On a roof with hardly any rust in evidence, there was a rectangular hole under the bracket on the corner of the roof.

Building lessons here include the need to do the math and figure out how much mastic tape and caulk is enough and inventory what the contractor has brought to the job. Second, don’t go cheap on the supply of screws. The contractor will push to finish the job, even if it means using extra security screws featuring odd shaped ceramic heads, which are a booger to remove during future maintenance efforts. Third, it is not just about grounding. It is also about continuous uniform surface. I recognize that mesh of a certain size meets the requirement, but again that is continuous and uniform.

The point of this is that DoctorPrepper is right. Metal buildings may dampen electromagnetic waves, but they do not come close to eliminating them. More layers of protection are required. Certainly there is a dampening effect, otherwise my cell signal would not be so lame in there.

And, to return to the original point, you can have an Internet connection as it was originally intended by its inventors with the magic that is electromagnetic wave energy. You can maintain it as an independent mode of communication, come what may, that is decentralized, self-healing, and resilient potentially able to provide valuable intel.

My wife mused out loud the other day about how interesting it would be to occupy my head for just 30 minutes. I think I had connected two dots while seeking a missing debit card that had no apparent relationship in her mind. The two women in my office, upon hearing the story in unison and spontaneously shouted, “Five minutes would be plenty.” Sorry if this adds up to more than five minutes, but hitting 1500 words is a real chore for the guy inclined to the one liner.

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