Recently one of our customers came in asking about sat
phones. Apparently, in the recent Dora the Explorer movie, she uses a sat phone
successfully while inside a house.
Things like this are portrayed all the time in movies. We
thought it would be fun to dispel some of these myths about how communications
work, and help people better understand what they are actually working with.
Myth #1: Satellite phones can work anywhere, instantly.
Satellite phones rely on, you guessed it, satellites.
Providers have a large number of these satellites orbiting around the earth.
For the most part, they provide constant coverage. However, as one drifts out
of range, you must wait for the next one to come along in order to have signal
Further, satellite phones must be able to see the sky. In
other words, you have to be outside, with a clear shot to the sky. You cannot
use a sat phone in a bunker, or a cave, or under water.
Myth #2: Radios can communicate across thousands of
Many war or apocalypse movies show people talking on 2-way FRS
radios from New York to North Dakota, or something equally ridiculous.
Radio waves are a natural phenomenon. We have harnessed them as a means of transmitting communications over distances. However, they are a wave. It helps to think of them like this, in order to understand their limitations. For example, if you imagine a wave of water, you wouldn’t assume it would go through a solid object like a cliff face or a building. Yet, often we expect radio waves to perform this feat.
Wave size & frequency
These waves have different properties based on the SIZE of
the wave. The lower the frequency, the larger the wave. The larger the wave,
the farther it goes. Very large waves literally travel by bouncing off the ‘sky’
and then the ground. Examples of larger waves include CB and HF waves. CB or
Citizens Band is 25Mhz.
Smaller waves/higher frequencies are used for VHF and UHF
radios. Devices in these frequency ranges are those most identifiable and
widely used as ‘radios’. These devices are in the 140-450 MHz range.
Cellular waves by contrast are very small, as a result they
have very short range. However, smaller waves are better at ‘bouncing’ off of buildings
and other structures. Thus, where a large wave would simply be deflected, the
smaller waves will bounce and allow for signal in urban areas. Cellular is in
the 700-800/1800-1900 MHz range.
The reason we can call someone on a cellphone in another area of the country is the ground infrastructure of towers built by the cellular networks. It isn’t the wave emitted by our phone actually travelling to that location instantaneously.
Power is another issue that impacts how far a signal will go. For handhelds, 5 watts is the maximum output (for safety reasons). Generally, they are good for around 3-8km. Mobiles (or truck radios) are around 30 watts. This can go up to 100km with line of sight, but certainly not thousands of miles!
Thus, the only way to communicate over massive distances
would be to use a low frequency with considerable power. And as we’ve seen,
even this isn’t predictable, as the wave may be disrupted by obstacles in its journey
as it bounces across the countryside.
The moral of the story? Don’t expect your poor little walkie talkie FRS radio to communicate across miles and miles! It is hampered by its power and by the frequency it is using.
Myth #3: Radios are indestructible
Again, in war and apocalyptic movies, the poor radios go on forever- through tsunamis, and earthquakes etc.
Radios are used for emergency communications because they don’t require infrastructure. Where cellular and satellite devices require many working parts in a system, radios just need one another and the same channel.
A few things to remember however,
- Radios require power like anything else- so you must have a way to charge the battery.
- Handhelds are often waterproof and to military specs. These ratings are generally for a certain duration and level of exposure (eg. immersed 2 meters for 30 minutes). Thus, military specs does not mean indestructible.
- Radios require certain elements to function properly. We already mentioned a power source. A second is an antenna suited to the frequencies you are using.
The technologies we sell are truly amazing. They perform consistently in tough conditions, with little care or attention. We have seen radios caked in mud that haven’t been serviced for years, that are still going strong.
We’ve had people drop, throw, and sink their handhelds and they keep going strong. You can’t do that with a cellphone!
The purpose of this article is to help you understand the parameters of the technology you are using. This will allow you to use it more intelligently and more efficiently.