Recently one of our customers came in asking about sat phones. Apparently, in a movie, someone uses a sat phone while inside a house. Then there is TV shows where the radio in ear bud communicates with crystal clear audio across the city, unless the show writers want it to fail. 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 may have to wait a while for the next one to come along in order to have signal again.
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 miles.
Some can, but not your typical two-way radio.
We use radio waves to transmit our voice or data over distances large distances. How far they can travel and be effective depends on the frequency, the terrain, and obstacles like walls. Ironically, you can often send a message to the space station easier than the other side of a mountain.
Wave size & frequency
Radio waves have different properties based on the length of the wave. The lower the frequency, the longer the wave. When conditions are suitable, longer waves can bounce off the upper atmosphere and reach across the ocean. Examples of larger waves include AM broadcast stations, amateur radio HF communications, trans oceanic marine and aviation backup HF communications, various military, and of course Citizen Band radios (though CBs use the upper part of the HF spectrum so ranges is limited unless conditions are favorable).
VHF and UHF radios are used in commercial applications like resource road radios, construction, emergency services, government agencies, and aviation. These devices are generally in the 138-500 MHz range with aviation being from 108MHz. The shorter wave lengths means they work best when you have a clear path from radio to radio, or radio to repeater. That said, they will refract over hills and bounce off surfaces like hills and buildings. It’s common to be able to talk to someone ‘around the corner’ but not in the next valley.
Cellular phones use higher frequencies which are even shorter, as a result they have very short range. However, shorter waves are better at bouncing off of buildings and other structures making them particularly effective in urban areas. Cellular is in several bands between 700MHz to 6GHz range with 5G being at the top end. As a general rule, a 4G capable ‘tower’ will have greater reach than 5G. The higher the frequency, the more signal is lost due to rain and vegetation. In particular with 4G and 5G, if you can’t see the cell site tower, you can’t talk to it (though the signals do penetrate non metallic walls with some signal loss).
Power and Antennas
Power is another issue that impacts how far a signal will go though in most VHF and UHF applications it makes less difference than you might think. 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. These can go over a 100km with line of sight, but it has little to do with the power of the transmitter. Power helps, but range is impacted far more by the type of antenna and location. A long antenna mounted in the center of the roof of a vehicle will out perform the same antenna mounted on the fender. Both will drastically out perform a ‘rubber ducky’ on handheld radio.
Myth #3: Radios are indestructible
In war and apocalyptic movies, poor radios go on forever- through tsunamis, and earthquakes etc, unless the radio failing is part of the story line.
A few things to remember however,
- Radios require power like anything else. You must have a way to charge the battery on your handheld radio and your truck radio wouldn’t work if the battery is dead either.
- 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). But military specs does not mean indestructible.
- If you don’t have an appropriate antenna, the radio won’t work. They don’t work under water or in caves either.
- If your radios are linked through a repeater and the repeater is dead, you
Conclusion:
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. But they are subject to the laws of physics, not Hollywood.