Cell phones help us maintain contact with friends and family throughout most of the continental US and much of Europe. But some of the areas that hold large-scale camping events have marginal cellular service.

A5406CA (cellular phone) open (Photo credit: Wikipedia)

These miniature marvels have limitations on the distance over which reliable communications can happen. Some sites have spotty service. Others have weak or marginal service. Still others are only served by one of the major cellular providers.

Cell phones provide essentially “line of sight” communications between your cell phone device and the cell phone tower. Many things can impact your ability to make or receive a call. The most obvious way to impact your cell service is to control the distance to the cell tower. If you are closer to a cell tower, reception will be improved. Being further away from a cell tower decreases reception. Generally speaking, cell phone reception will work within 12 miles of a tower site, providing the tower is “line of sight.” You may also be able to make calls from as far away as 22 miles from a cell tower.

Line of sight doesn’t strictly mean that you have a clear view of the cell tower. But some obstructions are deceptively opaque to the radio signals. Leaves of trees and bushes fall into this category. More obstructions mean less signal. Less signal means its harder to

English: The Faraday Cage is in the High voltage Lab of the University of canterbury Engineerig School. In the photo it was running at 110 000 volts, and the spark can be seen on the left where the technician is pointing a probe at the cage. (Photo credit: Wikipedia)

make and receive calls. Metal is the ultimate obstruction – if it is connected to the ground. Scientists use this fact to make Faraday cages to keep radio waves (that also make up cell phone signals) out of an area.

Signals can also be received even though a ridge is between you and the cell tower. And, sometimes you can see the cell tower very close to you, but you can’t get a signal. Both of these facts depend on how the cell tower signals are aimed by the antennas on the tower. What would be nice is a way to amplify the cell signals so that you can make a call when you are in a marginal area.

Your ability to connect to the cell service can be improved in many circumstances by using a cellular phone booster.

Wilson Electronics dB Pro Installation (Photo credit: nan palmero)

Cell phone boosters can use simple whip antennas (like a car radio antenna) or a jogh gain antenna like that shown to the left.

Lower cost cell phone repeaters can be purchased for $200-$300. These boosters come with a simple whip antenna – AND your phone must be placed on a special pad to boost the signal. These boosters are powered from your car’s 12V system and work well. But, be aware that you can drain your car battery if you leave the booster on continuously for a long while.

More capable boosters are also available but they involve more and larger equipment. The equipment includes an external antenna – most often a directional antenna as shown below.

Wilson Electronics dB Pro Installation (Photo credit: nan palmero)

Establishing cell phone service using signal boosting equipment is fairly easy but it does take some technical skill. Simple boosters with one antenna and a contact antenna for the cell phone are the easiest to install. Follow the simple directions. Establishing a link to distant cell towers is more complex and requires some knowledge of transmission systems – and takes some trial and error. All of these boosters include protection to prevent accidentally damaging the cell tower.  If you lack adequate skill to set up the more complex boosters, a local distributor may be able to provide you with training.

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Xantrex 175 watt DC-to-AC power inverter rebadged by Duracell. It has one grounded AC outlet and one USB 5v DC output. It can accept cigarette lighter auxiliary power or battery clips for input. It uses a soft switch for powering on and off. (Photo credit: Wikipedia)

To use an inverter as a source of power for tent camping – decide on the wattage that you will need..

Step 1: Determine what AC appliances you want to operate simultaneously. Add their wattage together and buy an inverter with 20% more capacity. For example, suppose that you want to operate a laptop computer and CPAP machine at the same time. Assuming a few numbers for our example: 75W (laptop typical) + 120W (CPAP machine – your machine will draw a different amount of power) = 195 watts. So, select an inverter of at least 234 watts. For most types of inverters the 20% additional capacity accounts for many manufacturer’s practice of over-reporting the real capacity of their inverter.

Step 2: Determining battery size. Divide watts * number of operating hours by 12 to get amp-hours. Multiply this number by the number of days that you need to operate your devices on battery. Multiply by 2 to determine the number of battery amp-hours required at a minimum.

Step 3: What kind of wire do you use to connect your inverter to the batteries? There are many types of wire, but you’ll want to use either the short wires that come with your inverter, or marine grade wires at least as large as the gauge of the wires that come with your inverters (the smaller the gauge number the larger the wire).  I recommend using one gauge larger than the chart to minimize voltage drop. Voltage drop wastes power and causes the inverter to operate outside its ideal design parameters.

Step 4: Connecting it together – Connect the negative lead for the inverter to the negative post of the battery. Connect the positive lead of the inverter to the positive post of the battery. Some inverters have an on/off switch that can be used to turn the inverter completely on or off. If your inverter does not have a switch you will need to either install a switch or be prepared to disconnect a wire to the battery in order to completely turn off the inverter..

Step 5: To charge your battery for use, disconnect the battery from the inverter  and attach the charger. The charger will take a variable amount of time charge the battery from house current. By using a smart charger you will fill the battery faster than a simple charger. Look for a charger that says “multistage charger.” You will need the charger with you if your batteries won;t last long enough for the entire camping event.

Step 6: Managing your battery. A 12V battery is fully charged when the resting voltage is 2.7V. To measure resting voltage, charge the battery and let it sit with no connections for at least an hour. Use a voltmeter to check the voltage level. Generally, batteries should be kept above 11.95V at a resting level. The fastest charging will occur between 11.95V and 12.5V. Plan to use your battery within this range when camping. NOTE: start with a fully charged battery at home and recharge (if electricity is available to you when camping). A 125Ah battery discharged to 11.95V will take about 7 hours to replenish the battery to 12.5V

For most weekend uses for small medical devices I’ve found that a single 12V 125Ah battery will suffice for most people using modern CPAP machines. As always, make certain that you know how to determine the power requirements for your specific machine. If you aren’t certain, engage a professional who can help size your system to meet your needs.

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