Like a police officer’s handheld radio is able to transmit to another unit let’s say 10 miles away, and he’s able to do that with ease. How is this possible? How come handheld radios that we have access to can’t do that? I know this probably sounds dumb to most of ya’ll but
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Most of the handheld radios you can buy without a license is limited to a power output of 10mW. This is almost nothing which means the signal can not go far until it is too low power to be picked up above the background noise. The size of the device is limited by the frequency and not power at these low power ranges. A cell phone however is a licensed radio managed by the network operator and can therefore transmit up to 2W on similar bands. So a cell phone can contact a cell tower miles away without much issues and can even go through light coverage such as a forest or wooden houses. This is mostly because it have 200 times more power then the radio which essentially gives it somewhere around 5 to 14 times the range.
Most handheld police radios are 5W with vehicle mounted models being 10-20W. So that is an order of magnitude more again. It is first at these powers that the physical size start becoming a problem as the batteries struggle delivering enough power. This is why larger models that can be connected to a permanent power supply can transmit at higher powers then handheld devices. In addition many police radios have relay stations, similar to cell towers. So two officers who want to talk to each other over the radio do not have to be in range of each other as long as they are in range of one of the relay towers.
The disadvantage of these high power radios is that you can not have many people using the same frequency at once. If there are different police activities happening even several tens of miles from each other they have to switch channels to not disrupt each other. This limits how much activity you can have in a certain area. For this reason, and to conserve battery life it is a common practice to turn down the power of these radios when not needed. So you can turn down the power to 1W or even 500mW when conducting local operations within a mile and then turn it up if you are further away from the people you are working with. Similarly the police will switch away from the channels that have repeaters when not needed.
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