Codan Radio Transportable Radio Systems User Guide - Manual (Page 24)

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4.7 Power Supplies
The fi nal key consideration in selection of the Transportable Radio elements is the power supply. How are you going
to power the repeater? The following sections outline the common power supplies options available for Transport-
able Radios with their associated trade-offs.
4.7.1 AC
AC Power is the simple power option — just plug the repeater into the “wall” and turn it on. This is only appropri-
ate for some applications as even the most urban deployments can fi nd a system with only AC power options very
limited in where it can be deployed. Either that or get a very long extension cord…
When using AC power as the primary source a number of considerations need to be kept in mind:
• If the system requires AC power, then each time it is deployed, the location selected must be within range of an AC
power supply. This may be a problem in some environments.
• Most rural locations will have very limited AC deployment options.
• Most electronic equipment runs on DC voltages. If AC power is the only desired source then an AC–DC power sup-
ply will need to be included in the repeater system which can add signifi cant weight, size and cost to the system.
• AC power cabling can get complicated when running closed-lid systems. Finding AC bulkhead connectors that
maintain the integrity of the power supplies electrical approvals is always challenging.
• Each country in the world has its own set of utility power characteristics. This means that a system that runs cor-
rectly in North America will need to be adjusted to run off the utility power in Europe.
• Having the capability to switch input AC frequency and voltage is benefi cial, but also requires careful monitor-
ing each and every time the system is powered on. If the wrong input voltage and/or frequency is selected on the
equipment, then damage may occur to the equipment.
Using a generator to produce AC power is an option but again there are a number of considerations to bear in mind:
• Generator power may increase the number of scenarios a repeater may be deployed in, but also adds a signifi cant
logistical issues into the deployment; fuel.
• Be aware that when using generator power as the sole source, generator maintenance will be a constant issue for
those on-scene.
Noise-Limiting — the noise of a generator will be an obvious giveaway during a stealth operation.
• If a lower-cost generator is being used for the system power, this can quite often introduce “dirty” power into the
system. This dirty power is noisy and can wreak havoc on a communications system. Even higher grade generators
may experience this problem if they are over-sized or for the load they are carrying. A large generator with a very
small load will run far less effi ciently than a generator with a maximum load.
4.7.2 DC
DC Power is the more common power option — connect the repeater to a set of batteries and you are opera-
tional anywhere. However, when using DC power as the primary source a number of considerations need to
be kept in mind:
• Internal Battery Power – Very simple to operate, just turn on the repeater. However, this comes with a number of
trade-offs. Internal batteries mean the repeater is heavier. The repeater will have a shorter run time as only small
batteries can be used. Users of the system must always remember to recharge the repeater between uses and the
repeater must be very effi cient with its current draw.
• External Battery Power – By adding a second case to the repeater system, signifi cant increases in run times can
be achieved as the external battery can be much larger than its internal relative. However, a second case is now
included in the deployment which adds costs, size and weight to the deployment.
• Solar/Battery Powered – By adding a solar panel to the repeater, it is possible to achieve extremely long run times
to the deployment. This is very helpful for deployments that will be for an undetermined amount of time such as a
Natural Disaster recovery or Forest Fire Response. This solution adds a third case to the deployment however and
the repeater itself needs to be very effi cient with its current draw.
• Generators – Offer a DC power output, however the need to provide fuel is a major consideration.
4.7.2.1 Solar Power
On a sunny day each square meter of the earth’s surface receives about 1 kilowatt of energy (1 Kw/m2). A solar cell
converts light energy into electrical energy. A cell’s current and output are directly proportional to its illuminated
area and illumination level. Voltage is unaffected by cell area, and is relatively insensitive to illumination level. Above
a low illumination threshold, cell voltage stays constant at around 0.5 Vdc. On the other hand current output, and
therefore its power, increases in proportion to illumination levels.
With advances in design, the mounting angle is not as critical as it was previously. A useful rule of thumb is to mount
your panel at an angle to earth equivalent to your latitude plus fi ve degrees. Remember to point the panel(s) true
south, towards the sun at noon.
An example of a transportable solar panel package is shown below. Packaged in a compact polyethylene case the
solar panel is lightweight, easy to carry and offers either 60 or 120 W of power. The Solar panels are rugged, compact
and lightweight. They unfold to a size of 6’ x 4’ yet fold up into a package that is the size of a laptop.
60 W Solar Panel