A Low Power Communications Station in a Bucket – Part 3, by Tunnel Rabbit

(Continued from Part 2.)

Photovoltaic (PV) Power

Power can be supplied by an internal or external source. For long-term fixed installation, a single wire pair can deliver power from a 12 to 24 vdc from a PV panel to a battery stored inside, or placed outside, or directly to the voltage step-down converter inside. A Baofeng battery eliminator can accept the higher voltage of a PV panel and step it down to 7.4 volts that the transceiver requires. However, there is no battery present to be charged and consumed after sunset, whereas with the voltage step down covert charges the transceiver’s battery. This is the most efficient use of PV power.

Anytime electrical power is converted into a chemical form and then reverted back to electrons (on discharge), there is power lost in the conversion, approximately 15% by some estimates. Bypassing a storage battery and a charge controller, and the usually long runs of DC wire that can represent an additional 5&% loss, improves the efficiency of a small PV system, greatly. And an expensive MPPT charge controller that can improve efficiency during cloudy periods is not needed. The step-down voltage converter is a homemade item, and is detailed in ny SurvivalBlog article Commo for Family, Group, and Community, Part 5. This allows one to use either solar direct power or battery operation, or both.

For the more sunny six months of the year, when no storage battery is used, 10 watts of PV power is a minimum for each one handheld transceiver that needs to be in operation 24/7,and when, and where one transceiver is turn on and receiving, while a second transceiver is off and charging from the same power source. As a minimum, 10 watts is needed for northern latitudes, because the crossband repeater has two transceivers that are turned on 24/7. Ideally, they should both be outfitted with the large 3800Mah batteries that will supply power during overcast days when the PV panel output drops to 10 to 20% of full production.

This is an alternate method as opposed to the standard cross-band repeater builds seen on YouTube, and as detailed in the book The Guerrilla’s Guide to the Baofeng Radio that uses a 5 watt panel, and a 7 Ah sealed lead acid battery. Typically these crossband repeater builds rely upon a small sealed lead acid battery, and a 5 to 20 watt PV panel. Except for the summer months only, their power supply design would not be adequate for latitudes nearer 48 degrees. During winter operation, 200 watts would be necessary to produce enough power to operate 24/7 during the long and dark months of winter where there is no storage battery, but only a transceiver battery used to store power. A 100Ah deep cycle battery added to the repeater would reduce the wattage requirement for northern latitudes.

During fair to good weather, a 100-watt panel would be adequate to keep all the transceivers, and repeaters in operation 24/7 when a storage battery is also being charged. In the winter, I would add another 100 watts, and not operate more than 2 Baofeng UV5Rs, or one mobile transceiver during this time. During the sunniest months, a foldable 21 watt panel from Ready Made Resources and a storage battery would work nicely for either a mobile, or up to 4 handheld transceivers, or 2 handhelds and one crossband repeater. During the long dark winter months at latitudes near 48 degrees, a 200 to 300 watt array and a storage battery would be necessary if only one mobile, a scanner, and two handheld transceivers need to be operated 24/7.

We could also use a commo window during the peak hours during ‘solar noon’ if a storage battery is not available, and turn off the transceivers to conserve power. A base station should however, have a receiver turned on to receive a call from an observation post at all times. If only one 100-watt panel were available, I would charge two Baofeng UV5Rs directly with the voltage step-down converter, and only have one of the transceivers turn on 24/7, and alternate between the two transceivers as their battery is consumed. This is the most efficient use of the PV power available. If at all possible, exceed the minimal PV array requirement estimated. Every location, and variables that are not possible to account for enter into the equation, and we would not want to be disappointed by the failure of a plan that is critical for a security operation. It is always better to have it, and not need it, rather than the other way around.

Repairing Damaged PV Panels

The larger PV panel shown is a new 100 watt panel, and the small one is a 10 watt panel that is approximately 10 years old. The glass was shattered, and repaired. A panel can be damaged during transport, by moisture intrusion, or by a bullet. We should have the materials and knowledge to repair a PV panel. If the glass is shattered, we can repair it by applying overlapping layers of clear packing tape, and as an additional protection, applying several coats of a clear polyurethane that has some resistance to degradation by UV. If hit with a bullet, remove the broken glass and bypass the damaged cell with a jumper wire. In either case, it’s serviceable life span would be extended by placing a sheet of glass, or plexiglass over the face of the panel, and sealing it to the frame. To be certain that no water infiltrates, orient the panel directly upwards. In austere settings where grid power is uncertain, or unavailable, PV panels of any size, or in any condition will be highly desirable, and difficult to replace.

Battery Power

Shown is a voltage converter supplying power from a ‘tired’ old car battery to charge 4 Midland GXT Talk About transceivers, and two Baofeng UV5R transceivers simultaneously. Note that one of the Midland GMRS transceivers is modified.) With a voltage step-down device, we can use any 10-to-24 vdc power source including a ‘tired’, or weak automotive battery. A battery that is good enough is one that maintains at least 12.1 volts while under a load created by transmitting on the highest power setting. If using a full-sized automotive battery rated at 500 Cold Cranking Amps (CCA) or more, or a deep cycle battery of 100ah in capacity, a PV panel of 20 watts or less can be connected directly without the use of a charge controller.

Without a charge controller, a panel array of many 100-watt panels could be used to charge a battery if the progress is closely monitored with a multi-meter. Temporarily disconnect the PV array and test for a maximum of 14.6 vdc though out the solar day. When the reading exceeds 14.6 vdc, disconnect the PV array. Although tedious, this method will keep the battery charged, and the station in operation. Lead acid batteries can tolerate over-charging, to a degree. But beware of the risk of explosions due to accumulated hydrogen gas, and locate the batteries outdoors, for this method of charging.

Trojan offers 12vdc deep cycle battery. It is too large to fit inside the bucket, but it would have a long service life in this role, and continue to provide power when most other choices would be exhausted. Two 6 volt Golf cart batteries from a big box, or automotive parts store would provide the most power and a long service life for a small communication station for the least amount of money invested. A small lawn tractor battery — Sealed Lead Acid (SLA) — available at a local automotive parts store that might cost $30 to $50 is ideal if a battery will be stored inside the bucket. It will have a relatively shorter service life if used for more than operating a low-power repeater. A small SLA battery can be installed above the internally located metal can that isolates the transceivers inside from the charge controller that should be located on top of the metal can, and protected in a plastic bag. A compact AGM battery or a standard SLA battery are the best choices. The metal can contains the transceiver and repeater box, and will protect the charge controller from the RF that can disrupt its function.

It is necessary to keep any device separated from corrosion that occurs in the presents of vapors containing sulfuric acid that escape from a standard lead acid battery, therefore, standard lead acid batteries should be located outside the bucket. In this photo of a Portalac battery, it is worth mentioning that it is available for those can afford this expensive, yet excellent (SLA) AGM 28Ah battery designed for very long life as a backup power source for telecom. These hold a charge for years without being maintained, and can be stored inside the bucket. I believe these batteries are a superior choice for this particular application. However, for the same price, we can almost purchase two 6-volt deep cycle golf cart batteries with 100 to 140 Ah capacity. Those, of course, would be much more bulky and heavy to transport.

To get the longest service life from deep-cycle batteries, cycle no more than 20 percent depth of discharge each day. According to Trojan Battery Company literature, the service life of its deep-cycle batteries would be about 8 years. In my experience, Trojan’s estimates are accurate. Aging batteries that once saw a depth of discharge of 50% per day, could provide that level of power for about 3 years. They can, however, remain useful for many years thereafter in a lower-demand role if the depth of discharge is greatly reduced. The communication station that is the Commo Bucket could utilize aging batteries for several additional years if supported by an adequately large PV array. The Portalac battery shown is approximately 15 years old, or older, well past its advertised 13-year service life. Fully charged, its voltage is only 12.5vdc instead of 12.6vdc which can be an indication that a fresh battery is fully charged. A low-tech homemade load test found it still has enough capacity to be serviceable.)

Testing Lead Acid Batteries

While a multi-meter can indicate a voltage level that leads one to conclude that the battery is in good condition, voltage readings are only an indirect measurement of the actual power stored inside. As the battery ages, its lead plates become increasingly sulfated, therefore using voltage readings as a method to determine the capacity, becomes increasingly less accurate. Low cost and accurate means to determine the state of it charge is performed by a hydrometer. This is an inexpensive and valuable tool when the time comes that we no longer take a battery to an automotive parts store where it can be load tested, and analyzed. Or we can perform an old-fashioned load test that could be just as valuable as it demonstrates its ability to provide power to a low-current drawing device over time.

The test involves a common 12vdc incandescent light bulb, or some other resistive load of a known amperage draw, a clock, and a volt meter. A type 1156 automotive lamp is a single-element light bulb that consumes 33 watts per hour, or 2.75 Ah (amps per hour). If the current draw is unknown, use a multimeter to determine the amount of current the load consumes. Then connect the load, start the clock, and monitor the voltage until the voltage drops to 12.1 vdc. If the load remains connected for only 1 hour, we can now estimate how long it might power a particular load such as a scanner by doing some math, 2.75Ah divided by 0.075Ah (the scanner or Baofeng UV5R) = 36.6 hours. For every hour the type 1156 light bulb is on and the battery voltage remains above 12.1 vdc, the Baofeng UV5R can be operational for a period of 36.6 hours. Because of scarcity, any battery that can be found would be potentially valuable and pressed into service. Having several methods of evaluating it will be a valuable skill.

Deep Cycle Versus Starting Batteries

Obtain the largest deep cycle battery that is affordable, and at least 200 watts of PV power for use during the winter months, and the service life will be up to 8 years if the depth of discharge is no more than 20% on a daily basis. A large enough PV panel should be used to keep a lead acid battery of any type and size charged to its full capacity, ideally by noon time each day. During the winter, a generator may be necessary to provide a bulk charge prior to dawn of the next day when PV panels are a much more efficient means of topping off the battery. We must budget and regulate the power used, and size the system to the estimated minimum power we expect to need during the shortest and darkest days of winter, so that a generator and fuel to run it are not necessary.

Here in high-latitude Montana, I use a rule of thumb of a minimum of 4 watts of PV power for every 1Ah of battery capacity when a deep cycle battery is being used. BTW, a Marine/RV battery is not a deep cycle battery. If a battery is rated in CCA, Cold Cranking Amp-hours, then it is considered to be a starting battery that is designed to have a low internal resistance, so that it provide a maximum amount of amperage needed to turn a motor over fast enough, and long enough, to start a motor. If it is not a deep cycle battery, I would use more watts of PV power per rated Ah capacity to prolong the service life of this type of battery. We need to be able to fully recharge it during the next day, even during overcast days.

A standard automotive battery that is designed to start a vehicle, including lawn tractors, is not designed for consistent deep discharges and long periods of discharged states. These batteries will be damaged and reduced in capacity as its lead plates become sulfated relatively quickly when used in these applications. If a Marine/RV starting battery is completely drained of power only once, 20 percent of its capacity can be lost. Each successive time a starting battery is deeply drained of power, a significant amount of its capacity is lost. After 3 to 4 occasions of near 100 percent discharge, starting battery may no longer have enough capacity to be useful in the role it was intended for. A Marine battery is not a deep cycle battery, and neither are some batteries that are marketed as Golf Cart batteries. The buyer needs to beware of marketing ploys, and uninformed salespersons.

This AGM battery is not a deep-cycle battery. It is a better choice than a standard SLA (Sealed Lead Acid) battery, because it has a very low self-discharge rate that makes it ideal for long periods of storage. It is shown as removed from storage from inside the bucket, and is setting on the floor next to the bucket. This allows transceivers that are in operation running the repeaters, and used for digital over laptop to be stored inside where these, and spare transceivers and accessories can remain protected from the elements. 2 microphones can be secured with microphone hangers attached to the side of the bucket, makes for good use of the limited working space.)

Low Power Repeaters

Relying on repeaters to complete a communications circuit comes with inherent risks as they can fail due to EMP, or other equipment failure, or be rendered inoperable just prior to an attack. A repeater should only be used if maintained in a secured location. As another consideration, a repeater increases the RF footprint. In mountainous regions where portions of the local population are separated by the terrain, it may be necessary, especially when very low-power FRS/GMRS transceivers, the most common transceiver, are the only transceiver available. In this situation, a very low-power repeater can provide the most benefit with the least risk of interception.

One benefit of using FRS transceivers is that their propagation is limited. FRS radios transmit with only 1/2 to 2 watts as a maximum, instead of the 4 watts that is possible with the Baofeng UV5R. I would be more comfortable using a repeater if FRS/GMRS transceivers were the dominant transceiver, and they likely will be. Using very low power, and directional antennas, and terrain masking can decrease this negative impact on COMSEC. If the repeater is very low power, and not used as a tactical repeater, it is of less concern. I would not use an FRS or GMRS frequency for tactical operations, since anyone can listen in.

As a substitute communications system, not unlike to an old-fashioned party line, the daily chatter may actually overwhelm a SIGINT effort by its volume of marginally significant information yielded from endless hours of monitoring undisciplined radio traffic. This kind of routine chatter can also be a conduit for disinformation, or used as a diversion to lead potential attackers to make their assault where our defenses are strongest, or to feign strength when our defenses are actually weak. Or, it could be used as distracting camouflage for important radio communications that could be digital. If there are not other frequencies and higher powered transceivers available, or directional antenna, the same repeater could be used by a security team. Ideal they would use one of the 150 digital modes on FLdigi, or at least a brevity code, if not both.

I would avoid using a repeater for tactical purposes as it is a weak link, and would prefer using a higher power setting, or better yet, a directional antenna, or bands such as high VHF that is MURS, or better yet low VHF such as CB, 6-meter, or 10-meter as the best choices. A repeater for tactical purposes is less likely needed as most of their activity would take place in an area less than a mile or two. A crossband repeater would be the best type of repeater to choose, when and where a defense must be extended. The benefits and risks of using a repeater instead of a low-power relay system, or higher-power transceiver on frequencies that negotiate mountainous terrain well, should be carefully considered. A single method does not need to be used to the exclusion of other methods that solve a similar problem. Mixing and matching methods creatively can resolve the problem as well.

Simplex Repeater

As a very low-power repeater (200Mw to 2.5 watts), the Midland GXT950 is attached to the Argent Data Systems simplex repeater and broadcasts via it’s fixed antenna. Adding a ‘tiger tail’, that is a counterpoise, to the transceiver improves the range.) This is the easiest type of repeater to use, because it is a plug-and-play and uses a single transceiver, and because any transceiver can use it without being programmed. It is dubbed a ‘simplex’ repeater, because it uses a single frequency. It is essentially a digital voice recorder that parrots what it hears, or transmits what it heard. Where it might be most practical is where transceivers are used that are not capable of ‘duplex’ operation, and don’t require the operator to program their transceiver in order to use this type of repeater.

It could be needed where most of the older model FRS/GMRS transceivers transmit with no more than 1/2 watt (500Mw) ERP with a fixed antenna. A repeater would be needed as a relay to assist some parts of a remote community that is spread out over several miles and separated y mountainous terrain. After 2017, the latest generation of FRS radio/transceivers are permitted to use up to 2 watts ERP on FRS. This is a significant improvement. In ideal terrain, where a repeater is not needed, a 2-watt GMRS handheld has a range of 1 to 5 miles in ideal terrain when communicating from one handheld to another handheld. A base station using 4 watts can talk to a 2-watt GMRS transceiver up to 8 miles away, in my terrain.

A Baofeng UV5R using 4 watts and connected to an external antenna could be used with this simplex repeater to service an area of 1 to 10 square miles. A Midland GXT transceiver using its lowest power setting of only 200 Mw, could service an area of less than 1 mile in diameter. Unlike the usual practice of attempting to service the largest area possible, we should attempt to service the smallest area possible that accomplishes our goals. Because MURS and GMRS/FRS are radio services a local threat would have access to, use a PL, or tone, on the repeater to block others from accessing it.

Some Useful Links

Note that there are similar cables available for Yaesus and other mobiles.

(To be continued tomorrow, in Part 4.)