The band between 400 and 410MHz is mainly used for radio astronomy and for various satellite services.
A very important frequency is 406MHz, the frequency of the EPIRB radiobeacons. These are small transmitters that transmit their GPS location to a satellite when they are activated. They can be used by aircraft and ships (and their crews) when they are in distress. The satellite picks up these signals and relays the relevant data (location and identification of the beacon) to the relevant authorities such as the Coast Guard.
The band between 410 and 470MHz is used for landmobile communication in most parts of the world. In the 1970s, landmobile services started to use the UHF bands. This started only when solid state technology was sufficiently advanced to make solid state UHF transceivers feasible. The VHF bands had become sufficiently congested, so that use of the UHF band became necessary.
UHF does not suffer from sporadic E propagation, which is an advantage for short range communication. This is a problem on the low VHF bands (especially on frequencies below 50MHz).
For handheld transceivers, UHF has another distinct advantage over VHF. A reasonably efficient transmitting antenna has to be at least a quarter wave long. On VHF (around 150MHz) this means an antenna length of around 50cm, while on UHF an antenna length of 17cm would suffice, which is much less unwieldy. Low VHF bands would require even longer antennas. The police in The Netherlands used UHF mainly for handheld transceivers. They used frequencies in the band 466.5-469MHz.
The band between 410 and 430MHz is mainly used for analog and digital trunking networks in The Netherlands. Digital trunking networks use the TETRA system, analog trunking networks use narrowband FM. In a trunking network, users do not have fixed channels, but the system (computers at the base stations) selects a free channel for a particular conversation. Each trunking network uses digital signaling to tell the mobile stations which channel they must use. Using a scanner it is possible to monitor trunked communications, but it is not simple to pick out the desired communication from all active channels. In some countries (such as the USA) public services, such as the police used analog trunked networks. Scanners were available that could keep track of the various users of a trunked network, so it was possible to scan just the desired police channels.
The mobile phone network is also a trunking network. From 1985 to 1999 The Netherlands had an analog mobile telephone network around 450MHz. This network had 222 channels with 20kHz spacing. The same system was used in Belgium, The Scandinavian system on which it was based, used 25kHz channel spacing and was not interoperable with it. The following channels were used:
In the USA the 70cm amateur band runs from 420 to 450MHz. European radio amateurs are less lucky. In most European countries, this band runs from 430 to 440MHz, in some countries this band is even narrower. Fortunately The Netherlands has the full 430-440MHz range.
As in the 2m band, the 70cm band is divided into several segments for different types of uses. There are segments for local FM communication, for long distance CW and SSB communication and for satellite use. Repeater channels are also allocated. While all repeaters in the 2m band use a +600kHz shift, the UHF band uses both -1.6MHz (repeater output 1.6MHz lower than input) and +7.6MHz shifts. The Netherlands uses a -1.6MHz shift.
While sporadic E propagation is non-existent, tropospheric conditions are prominent on this band.
Radio amateurs have the privilege of constructing satellites, which can be launched into orbit as a secondary payload of other satellite launches. These satellites are commonly called OSCAR. These satellites contain several different types of transmitters, such as beacons, telemetry, packet mailboxes and linear transponders. A linear transponder receives a small band segment (say 30kHz wide) and retransmits it on a different band. So a satellite may receive in the 2m band and retransmit in the 70cm band. Several amateurs may use the same linear transponder at once. By using SSB or CW, one needs only a small portion of the total transponder bandwidth. Because the satellite moves with respect to the (stationary) radio amateur station, a Doppler shift exists. On 70cm this shift can be a few kilohertz, more than the total bandwidth of an SSB voice channel. Using a linear transponder requires great skill. Not only do you need to move the antenna to keep it pointed to the satellite, you must also retune both your transmitter and your receiver frequency to compensate for the Doppler shift.
The 70cm amateur band is the first band that is wide enough to accommodate a TV channel. The European band is only wide enough for a single TV channel. Amateurs are allowed to transmit TV signals on 70cm using the same system as (analog) broadcast TV. Many TV sets can receive the signal using a suitable antenna. Modern TV sets essentially cover the entire frequency range between 41MHz (Europe) or 54MHz (USA) till the top of the UHF broadcast band, as some cable networks make use of frequencies between the regular broadcast bands. Radio amateurs are allowed to transmit in FM stereo on 70cm (some do), but it not allowed to transmit music.
In Europe there are two bands in which it is allowed to transmit without a license. The LPD band (low power devices) runs from 433.075 to 434.775MHz (69 channels). It is also an ISM band. It overlaps with the 70cm amateur band. Allowed transmitter power is limited to 10mW and devices must have a fixed antenna. It can be used for several purposes, such as cordless headphones, car door openers and voice communication. The problem is that radio amateurs are allowed to use a power of up to 400W on those same frequencies. In The Netherlands, licensed radio amateurs (using 70cm equipment) are allowed to communicate with users of unlicensed LPD transceivers.
The other unlicensed band is the PMR446 band (8 channels between 446.0 and 446.1MHz). There is also a digital PMR446 allocation between 446.1 and 446.2MHz, but equipment is not widely available, so the band is not widely used. Allowed power is 0.5W and there is no interference from radio amateurs. The only problem is that there are only 8 channels. It is possible to use CTSS tones (tone squelch). The transmitter transmits a low frequency audio tone (60-250Hz) with the signal and the receiver only opens the squelch when the same tone is received. This way a user only hears the transmissions on the channel that use the same CTSS tone. So if two user groups (two businesses) use the same channel with different CTSS tones, they do not hear each other's communication. However this provides no privacy, as a receiver with CTSS disabled will hear all communication on that channel. Radio amateurs use CTSS mainly on repeaters (the repeater is activated only by a signal with the correct CTSS tone).
In the USA the FRS (Family Radio Service) is license free with 14 channels in the 462 and 467MHz band. It is comparable to PMR446. GMRS (General Mobile Radio Service) does require a license, but provides more channels and more power. A license for GMRS is easily obtained.
In the 1990s some radio pirates in The Netherlands operated in the range 480-500MHz, which they called the 60cm band. They transmitted in wideband FM (mostly stereo). They could not reach the general public, but they could communicate among themselves. The chances of being caught (and the repercussions when caught) wer much smaller than when using the FM broadcast band.
In the USA, the UHF band used to run from 470 to 880MHz, containing TV channels 14 through 83 (each 6MHz wide). The portion above 800MHz however, has been taken away in 1983 for landmobile communication and mobile telephone. In Europe the band runs from 470 to 862 MHz and contains channels 21 through 69 (each 8MHz wide). Channels 13 through 20 have never been allocated in the standard European channel plan, but they were reserved just in case the TV bands would be extended. Cable networks can use channels between the official broadcast bands.
The UHF band is called broadcast band IV (470-608MHz) and broadcast band V (614-960MHz). Originally the broadcast band would extend to 960MHz, but the channels above 860MHz have never been used. The band between 608 and 614MHz (corresponding to channel 38 in the European band plan) has been reserved for radio astronomy. No transmitters on earth are allowed transmit on these frequencies, so that radio telescopes can pick up extremely weak signals from space without interference.
In the USA, TV was already very popular in the late 1940s end only 12 VHF channels (2-13) were available. There was a great shortage of TV channels, right from the start. UHF TV channels were already used around 1950. In the early 1950s they were already experimenting with a color TV system that was incompatible with the existing black and white system. They planned to use the UHF band for color TV and the VHF band for the old black and white system. In 1953 however, RCA introduced the NTSC color system, which was fully compatible with the existing black and white system and did not take more bandwidth. From then on it was clear that the UHF band would be used for regular TV channels (color or black and white). Even in the early 1960s not all new TVs came with UHF tuners. For (commercial) broadcasters this meant that a UHF channel had fewer viewers than a VHF channel, so UHF channels were much less desirable. A special law was required (the All Channels Act) to force manufacturers to equip all TV sets with UHF tuners.
In Europe the UHF band started to be used in the mid 1960s. The Netherlands (which had only one TV network) started to transmit the second network on UHF. Special UHF converter boxes were available, so users of existing (VHF only) TV sets could watch UHF channels. In The Netherlands they were called "Tweede net kastje" (second network box), because you needed one of them to watch the second network. In the 1980s a third TV network was introduced (also on UHF).
For UHF you need a suitable TV antenna. This can be a Yagi antenna, but it is rather hard to construct an antenna that covers the entire band. Alternatively you can use a log-periodic antenna. From a distance a log periodic antenna looks like a Yagi antenna, but all elements are connected to the feed line (in a Yagi antenna there is only one actively fed element). Such antennas can be made sufficiently wide band to cover the entire VHF and UHF spectrum. Starting in the 1970s most cities and smaller towns introduced cable TV. Cable TV offered more channels than most people could receive with their own antennas. At the same time they banned rooftop antennas. The Netherlands is one of the countries with the highest percentage of cable TV viewers.
In the late 1980s you could watch NTSC television in The Netherlands, if you lived close enough to Soesterberg. The AFN transmitter operated on one of the top channels in the American band, just outside the European TV band. You needed an NTSC compatible TV set, which was not readily available in The Netherlands. As this was not considered a real broadcast transmitter, cable networks were not allowed to carry this signal (they were allowed to carry AFN radio channels).
The Netherlands was the first country in the world to stop all analog over-the-air broadcasting in 2006. Cable networks still carry analog signals. Over-the-air terrestrial broadcasts are all digital in The Netherlands and many other European countries. Analog TV broadcasting should be switched off completely in all of Europe by 2012. European countries use DVB-T, mostly in the UHF TV band. The space occupied by a single analog UHF TV channel can carry 5 digital channels. In The Netherlands, the DVB-T network is operated by a commercial party and viewers need to buy a subscription to get all channels. However, the public TV and radio networks are free-to-air (so you can watch them without a subscription).
The USA switched off most of its analog TV transmitters in 2009 and used ATSC instead. ATSC requires only on sixth of the bandwidth to transmit the same number of TV channels. More bandwidth is required for high-definition television.
Because digital TV uses less bandwidth than analog TV, both Europe and the USA are planning to reduce the amount of spectrum allocated to terrestrial TV and use it for other purposes (e.g. mobile Internet).The Netherlands is planning to reuse the 800MHz band and the USA is planning to reuse the 700MHz band.
See you next time when we discuss the higher UHF bands.
The transition to digital television, which is now complete nearly everywhere in the world. has reduced the demand for spectrum for terrestrial television, in part because digital television is more spectrum efficient (more TV programs fit into the space of a single analog TV channel), in part because digital TV is not susceptible to adjacent channel interference and less susceptible to co-channel interference. The result is that the top part of the UHF TV band is withdrawn from broadcasting, both in Europe and in America. In Europe the 800Mhz band will be used for 4G mobile networks (fast mobile internet), in America the 700MHz band will be allocated to mobile data services as well.
I added a band diagram. In Europe they also plan to allocate the 700MHz band to mobile data services. Digital terrestrial television will move to the DVB-T2 standard in the next few years, meaning that more channels can fit in less bandwidth.