Mobile Phone Frequencies

Steve White G3ZVW looks at the characteristics of the different frequencies used by mobile phone operators.

highest frequency UHF TV channel, was centred on 850MHz. These eight channels weren’t used for main TV transmitters, only for low power infill transmitters. They ceased being used for TV after digital switchover was completed in October 2012 and were subsequently reallocated for mobile phone use.

These frequencies offer some penetration into valleys and buildings, and therefore the greatest coverage areas. The total allocated bandwidth is 140MHz. This may seem a lot, but there are a couple of things that need to be thought about. Parts of it are for base stations to transmit, parts are for phones to transmit, and parts of it are intentionally not used (so-called Guard Bands). Also, nobody gets all of it because it is shared between all the mobile phone operators. When you consider the potential coverage area of UHF in combination with the explosion of mobile data usage, it adds up to not being able to support large numbers of simultaneous users, even though many base stations divide their coverage into three beams. Some masts are shared and have antennas from more than one operator, but Fig. 1 shows a mobile phone mast for a single operator. The antennas are protected under covers that are transparent to radio waves. What’s ‘under the hood’ is complicated and beyond the scope of this feature, but there will be antennas for 800/900MHz and higher frequency bands. Note that the antennas point out at 120° intervals. There is little overlap between the coverage of the three antennas, so as Fig. 2 shows, a network operator can effectively make the cell work into three separate areas.

These days the base stations on these frequencies tend to be away from cities, i.e. in places where the population is well spread out and the number of users is relatively small. In thinly populated areas the base stations are often located on hilltops, to give coverage into neighbouring valleys, Fig. 3.

1400-2600MHz

There are five separate bands in the 1400 to 2600MHz range, all in the lower microwave part of the frequency spectrum.

With greater bandwidth, larger numbers of simultaneous users can be supported. Use of these frequencies results in less coverage, so these frequencies work better in more populated areas where the network designers want to provide more than one cell, each with limited coverage. Microwaves don’t penetrate well into valleys, so network designers exploit this characteristic and intentionally limit coverage by not locating base stations on hilltops, Fig. 4.

Note that in Fig. 4 the shadow areas at the edges of the illustration are larger than they are in Fig. 3. The shadow areas would likely be catered for by base stations further away, but for clarity I do not show them.

These days there is a great deal going on in this part of the frequency spectrum. You can find out everything by downloading a document from the Ofcom website, but because it is very long and complex I am just going to give some highlights here.

Above and below the 1450-1496MHz allocation is where navigational satellite systems (GPS, Glonass and Galileo) transmit.

At one time WorldSpace satellite audio was broadcast around 1500MHz.

Have you ever heard of DECT? It stands for Digital Enhanced Cordless Telecommunications. Modern domestic cordless telephones are DECT and operate on 1880-1900MHz.

Communication with spacecraft takes place on 2110-2300MHz. For example, the Voyager spacecraft that was launched in 1977 is still in communication with Earth on 2114MHz (uplink) and 2296MHz (downlink).

In North America digital radio is broadcast from satellites on 23202345MHz, so the 2300MHz allocation for mobile phones isn’t relevant there.

Bluetooth works at 2400MHz. Some radio-controlled models and devices such as garage door openers do too.