A UHF transmitter like this gets a modulated carrier wave and sends it out. Radio waves have a frequency measured in MHz, and a UHF transmitter can broadcast from 300 to 3000MHz.
UHF radio is used for local and regional radio communications. The transmitter sends its signal using a carrier wave bouncing up and down between two antennas.
The wave is a combination of the power of the transmitter and the antenna. Since wavelength increases as the square of the frequency, we can see that the more power we put into it, the more wavelength that will be made.
So if we put twice as much power into the wave and double its wavelength, the signal will be doubled. So if we double it again, it will be tripled!
How far can UHF go?
The farther a radio wave can travel from its transmitter, the higher the power output must be. Since antenna height is limited by practical considerations, transmitters generally have to operate at higher power to send their signals long distances.
To send FM broadcasts across the nation, we would likely use a 100kW transmitter or more! A UHF TV broadcast station may use 5000-10,000 watts of power at UHF (470 MHz) and 3500-7000 watts at VHF (channel 2). The transmitter sends its signal using a carrier wave bouncing up and down between two antennas.
A similar process occurs with a cell phone or walkie-talkie. The signal is modulated by the transmitter’s output to a new frequency. It is then sent out over that frequency, then received several times by the antenna.
The result of the extra signal reflections is an advantage over FM. The more signals bounce off each other, the more like an FM broadcast appears when received.
Does UHF go through walls?
The carrier signal, meaning the message the transmitter is sending, is modulated by the signal from the transmitter itself. The carrier and modulator frequencies are equal and synchronized with each other. At a distance, a receiver can detect this signal and tune in to it.
When radio waves travel through the air within a building, they experience several effects:
UHF transmitters can be used for any commercial purposes, such as public address systems for sports events or outdoor advertising for businesses.
They can also be used to provide high-speed communication between vehicles in a race car or airplane flying overhead and on motorways or roadsides (for example, an emergency response team using UHF frequency).
A UHF radio can send in the short range and through walls. A UHF radio has an advantage over FM. This is because two or more signals can interfere with each other like FM but much more so (like how two or more TV stations can all go on air at once).
This is what cell phones do when you get a weak signal and it cuts out, but the limiting factor is still the transmitter. At a distance, a receiver can detect this signal and tune in to it.
Do police use VHF or UHF?
There is no “better” or “worse” between UHF or VHF. It’s all based on where you are, what you’re trying to do, and what equipment you have at your disposal.
When a radio wave travels through a building, it experiences several effects:
When police are on the move walking around in the city using VHF and/or UHF radios (or snipers), they will use VHF almost only. In big cities with tall buildings, VHF is used. It can penetrate walls better (albeit with a smaller range) than UHF.
On airplanes flying near each other, they will use both UHF and VHF since the requirements are different there. Police will also sometimes use UHF while on the move if they want to cover a very large area with a single frequency.
When the police are responding to some sort of situation and they know exactly where the other officers are, then they may use UHF with their body or car radios since it gives them better range.
In this case, the receiver is close enough to the transmitter that it’s not experiencing much interference from reflections off nearby buildings and in this case, UHF is preferred over VHF. The main point here is that it depends on where you are and what you’re trying to do.
When a police officer is using a UHF radio to talk over the air, he can avoid any possible reflections from nearby buildings.
This is why so many police cars feature long antennas sticking up into the air. This is also why airport security requires you to point your radio away from other people.
The UHF system is also complicated by frequency-selective fading, where variations in the ionosphere can change the effective shape of the antenna at a particular frequency. This changes its resonant frequency, thereby changing its effective length as well.
As a result, it can be difficult to build a UHF antenna to give the best performance on all frequencies over the whole design bandwidth.