Streaming to an Airstream

-June 12, 2017

I joined the “location neutral” crowd a few years ago when I retired from Agilent Technologies (previously Hewlett Packard, now Keysight Technologies). My job as an industry consultant and writer of EDN’s Test Cafe blog can be done from any location—my home office, or while visiting friends, or perhaps a hotel while traveling internationally. I’ve done all of these. In fact, my “office” is anywhere I can find an Internet connection and a cell signal.

And there lies the rub. My wife and I love the outdoors, and have taken a liking to camping. After years of tent camping, we recently bought a 2006 Airstream travel trailer, specifically a 16 foot “Bambi” model. It is pure luxury compared to a tent. My plan has been to do work and stay connected from our camping spots. However, many beautiful spots are far from reliable cell signals. It has been our experience that many cell signals will be on the very edge of detection, perhaps a single bar that would allow a text message at most, or fading in and out of service. Worse yet, an Airstream is essentially a Faraday shield, further attenuating the received signal.

My Airstream is shown parked next to the Vedauwoo’s unusual rock formations in rural Wyoming. Powered only by a 12V battery and solar panel, the objective is to snag and amplify a cellular signal for real location neutral connectivity. Image courtesy of Karen Desjardin Photography.

And don’t expect 5G to help this in the future. While 5G boasts uber speed rates, it will do nothing to extend the range of coverage, as most 5G mmWave signals will be constrained to 200 meters. Faced with this, I decided I needed to boost the cell signal in both directions from my remote site. Here were my requirements:

  1. The cellular booster must operate from 12V power, as that will be the only power source in the Airstream while camping. It should draw a minimum of power, and be able to be recharged with solar cells.
  2. I needed a two-way amplifier. It needs to amplify a weak external signal, but also needs to boost the power from my cell phone going back to the cell tower.
  3. I happen to be a Verizon subscriber, so the amplifiers must be capable of amplifying the spectrum bands used by Verizon. My plan is to use my iPhone as a hot spot for Internet connection. 
  4. I have some flexibility on antennas. My workspace will be the table of the dinette at the front of the Bambi, so that is the only place I care to have the superior performance. I am also willing to temporarily mount an external directional antenna to achieve maximum performance.

I positioned a directional Yagi microwave antenna to capture a faraway LTE signal. Image courtesy of Karen Desjardin Photography.

I researched amplifiers and cellular boost systems from weBoost, the cellular boost brand from parent company Wilson Amplifiers. I decided to go with the Drive 4G-X system, but modify the antenna choices. The Drive 4G-X system is aimed at mobile cellular boosting, such as in a car or truck. It had many advantages—it operates from 12V, it covers from 700 MHz to 2100 MHz (covering the Verizon and AT&T bands), and it boasts up to 50db of gain.

But it isn’t perfect for my application. The Drive 4G-X comes with two small antennas. One is a magnetic external antenna for the roof of the car and truck. The other is a candy bar sized interior antenna that delivers the amplified signal only within a foot or so of the phone. I wanted the best performance I could get, so I chose to upgrade both. For the external antenna, I chose a directional Yagi microwave antenna, with a specified 10.6db of gain. For the interior antenna, I chose a desktop antenna made to cover a desk area with 3.4db of gain.

Sounds good, right? There is a problem. The antennas have a cumulative 14db of gain. Add that to the 50db available from the amplifier, and you have 64db total. While that is great for capturing a weak signal, it also makes it prone to oscillation. That is, if the amplifier detects its own signal, it can be driven into oscillation and then shut down. This combination of antennas is not specified to work together unless the antennas are at least 20 feet apart. Difficult with a 16 foot Bambi.

Oh, but I’m an electrical engineer. The antennas’ gain has two big benefits—the improved performance in the direction of the signal, and the reduced power in all other directions, thus diminishing the threat of oscillation. Also, the shielding of an Airstream helps me now, attenuating the reradiated signal between the external and internal antennas, also reducing the chance of oscillation.

So my plan went like this: Install the amplifier into the Bambi, with the internal desktop antenna nearby. Bring a bike stand and a PVC pipe for mounting the directional antenna, along with 20 feet of high quality cable. Position the antenna location and direction so that the antenna faces the cell signal, but away from the internal antenna.

So, how did it work? Click ahead to the next page for the results.
Next: The results

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