This time we talk about the rest of the low VHF band (below the FM broadcast band). In this part of the spectrum, antenna sizes become more manageable and sporadic E is a nuisance less frequently.
In Europe, VHF TV band I runs from 41 to 68kHz and in the standard channel plan there are only three channels: 2, 3 and 4. Channel 2 has essentially been unused for a long time and the other two channels are likely to be completely abandoned in a few years. The plan is to abolish all analog TV transmissions by 2012 and digital TV transmissions are unlikely to be allocated on those low channels. Some people propose to use the low VHF TV channels for digital radio broadcasting (in DRM+).
In The Netherlands, the first program was transmitted on channel 4 from Lopik in the central part of the country for more than 50 years. In 2006 this transmitter was shut down along with the other analog TV stations.
Some European countries have different channel allocations. Italy has the C channel, which is very close to the FM broadcast band. North America has five channels (2-6) in the band between 54 and 88MHz, The audio carrier of channel 6 can be picked up by most FM broadcast receivers. Some TV stations in the USA use a TV broadcast license on channel 6 primarily to transmit radio programs.
TV channels in the low band are susceptible to sporadic E propagation and the very lowest channels (below 60MHz) are even sometimes reflected by the F2 layer, making intercontinental TV reception an extremely rare, but possible event. The multitude of TV standards in Europe made TV DX sometimes hard. So the 405-line transmissions from the UK could sometimes reach The Netherlands, but TV sets for this standard were almost unobtainable. So you had to tweak an existing TV set our you had to import a TV set from England. In any case you had to spend either much time or much money and only the most serious DX hobbyists would consider doing this.
In the late 1960s all European countries decided to move to a 625-line TV system, but this did not mean that the system was completely standardized by then. France kept using positive modulation and AM sound, while the rest of Europe would use negative modulation and FM sound. The sound carrier has an offset of 5.5MHz to the video carrier in most countries, but not in the UK, where it was 6MHz. Most other European countries however, used the same standard. Belgian TV was viewable on a Dutch set.
In 1953 the USA introduced NTSC color television. They interleaved a color subcarrier into the TV signal in such a way that it did not require more bandwidth than a black and white signal and that the same TV signal could still be viewed on black and white sets. The PAL system in Europe (invented in 1963, deployed in 1967) had the same properties. Europe used a second system, SECAM, which was used in France and most East European countries. Eastern Germany used SECAM and Western Germany used PAL, but their TV signals were compatible otherwise. So a TV set from one country could pick up the TV signal from the other country, but it would only show it in monochrome.
During most of the day, many TV stations would transmit a stationary test picture. By photographing the TV screen with a very long exposure time, it was possible to get a recognizable picture from extremely weak signals. Some TV DX hobbyists did just that. Other hobbyists specialize in detecting just the video carriers of distant TV transmitters. Using narrow band receivers (CW mode), extremely faint carriers can be detected. As the carrier frequencies of TV transmitters on the same channel vary extremely slightly (by just a few Hertz), it is possible to identify the station by measuring the frequency very accurately.
Most countries in Eastern Europe (except the German Democratic Republic and Yugoslavia) used the band between 65 and 74MHz (OIRT band) for FM broadcasting, instead of the regular FM broadcast band. As sporadic E propagation occurs regularly on these frequencies, these stations could regularly be heard in The Netherlands. The lowest part of this band was usually blocked out by the TV transmission on Channel 4. Around 1990 I once heard lots of these stations when I visited a fellow amateur. I have never heard them on a receiver of my own. Even though West-Germany bordered to Czechoslovakia and OIRT transmissions could be heard in the border region, it was illegal to possess a radio for these frequencies. Of course some radio hobbyists listened to these stations clandestinely. Since 1995 most central European countries have been moving their FM stations to the normal FM broadcast band. As of 2010, Lithuania is the only EU country that still has OIRT band transmitters. Most former Soviet republics have them as well. All of these countries have the regular FM band as well and are in the process of relocating their FM services. Broadcast radios for the OIRT band are essentially no longer produced, though some Chinese radios have an FM range from 64-108MHz, so they do receive this band.
A special FM stereo system was developed for the OIRT band, but apparently this was not widely used. The regular FM stereo system was used instead, so if you used a modified stereo tuner or a converter, you could receive the OIRT signals sometimes in stereo.
Japan is the only country in the world that uses the band 76-90MHz for FM broadcasting. Many Asian made portable world receivers have an FM range from 76 to 108MHz, so they cover both the Japanese and the normal FM band. It is essentially impossible for Japanese FM stations to be heard in The Netherlands. F2 propagation is no longer possible on these frequencies and sporadic E does not have enough range.
The UK allocated the band between 70 and 70.5MHz to radio amateurs, in return for the 5m band that was taken away. This band is called the 4m band. For a long time the UK was the only country that had this band.
Only since a couple of years do other European countries allocate this band to radio amateurs. However, The Netherlands is not yet one of them. Until 2006, the close proximity to TV channel 4 was the official reason. Apparently the Dutch military are opposed to it, as they use this band as well. They yielded the 6m band only reluctantly and apparently they were promised that no further amateur bands would be allocated in "their" low VHF band. Of course Dutch amateurs are free to listen to amateurs from other countries in this band.
On VHF the use of a manually tuned radio is not very satisfying. Either you hear only a single channel or you hunt for busy frequencies, only to arrive there late. A scanner can automatically switch between a set of fixed frequencies and stop when there is a signal on one such frequency. The first scanners had only a limited frequency range, a small set of channels that they could scan and for every single frequency you needed to purchase a separate crystal. In the beginning, scanners and the required crystals cost a fortune.
Early scanners available in The Netherlands covered only (part of) the VHF low band (68-88MHz) and (part of) the VHF high band (148-174MHz, but mostly only 150-170MHz). They had between 8 and 20 channels. Later the UHF band (450-470MHz) became standard. Around 1980 a scanner crystal for a commonly used frequency cost around 10 guilders (4.50 Euros), but at that time computer controlled scanners were already on the market.
The use of a PLL synthesizer eliminated the need to purchase a separate crystal for each frequency. Most scanners were computer controlled and you could directly enter the desired frequencies on a numeric keypad. It was also possible to search a frequency range for active channels. Some early PLL synthesized scanners used optically readable cards that you had to program by filling in a binary code for each frequency used. These cards cost money, but much less than crystals (and in a pinch you could make your own).
Most scanners covered the VHF low band (e.g. 68-88MHz), the VHF high band (e.g. 144-174MHz) and the UHF band (e.g. 430-470MHz). The exact band limits could vary for each model. More expensive scanners had the air band (108-136MHz) as well. A low VHF band (e.g. 26-54MHz) would come next.
In the 1930s, frequencies around 70MHz were already used occasionally for landmobile communications (communication with moving vehicles) in The Netherlands.
In many European countries this band between 68 and 87.5MHz was extensively used for landmobile communications. In the USA this band is used for television, except for a small section between 72 and 76MHz. In Germany this band was known as the 4m band. It was (and still is) used by the police, the fire department and ambulance services. The band between 74.8 and 75.2MHz is used for aircraft navigation beacons worldwide.
In The Netherlands we had police in this band, but also private companies. The ANWB (the Dutch equivalent of the Automobile Association) used frequencies in this range for its repair vehicles. The first mobile telephone system also used this band. I remember tweaking an old FM radio in the early 1980s and hearing those phone conversations around 85MHz. By that time, only ministers and captains of industry had mobile telephones in their cars. It was a mostly manually operated system, requiring a (human) operator to complete a connection and requiring manual channel selection.
In The Netherlands, the most important police channels were located around 87MHz, so they could be picked up by an ordinary FM broadcast radio. Even in the early 1950s, when FM broadcast radios first arrived in the home, these frequencies were already used for police communication. Many people were drawn to scanning by first trying to listen to police communications on a normal radio. The fact that police communications could be heard on an ordinary radio, possibly helped reinforce the idea that it would be futile to ban scanners. In the early 1980s there were plans to ban scanners, but scanners proved to be too popular. In Germany on the other hand, the police channels were a few MHz lower, so you could not hear them on an ordinary radio.
Sometimes the police did not want the general public to overhear their conversations. In the late 1970s they used simple voice inversion scrambling to make their signal unintelligible. However, this was not very effective. A more advanced system was used in the 1980s. In this system the speech signal was digitized and cut into many small 100ms fragments which were transmitted in a different order, some of them played backwards. Decrypting this was out of reach of the hobbyists of the time. In the 1990s the police had an all-digital system with real encryption. The police used encryption selectively however, only for very sensitive information.
The Netherlands used a paging system called "semafoon" between the 1960s and 1990s. Each subscriber carried a small VHF receiver that would react to a unique tone code and then display a single digit. At least these receivers were small in the 1980s, those that were around in the early 1960s were a lot bulkier. By dialing a special telephone number, one could order this code to be transmitted. This way the boss could call up one of his service workers. The frequency used was even closer to the FM broadcast band than the police channels. When listening to a wide band FM radio, one would hear the characteristic tone sequences of this paging system when no police channels were active.
In many countries the possession of non-broadcast receivers for VHF and UHF is strictly regulated and it is illegal without a license. In many other countries, possession is legal in principle, but the use of such receivers is severely restricted.
According to EU regulations, the sale and possession of receivers for any frequency range is free in principle. What you do with those receivers is a completely different thing. So in principle it would be legal to use a scanner for listening to the 2 meter amateur band in any EU country. In The Netherlands, Denmark and Sweden the use of scanners is completely free. In many countries, such as the UK, Germany, Belgium, France and Spain, listening to anything but broadcasts and radio amateurs is illegal. However, the level of enforcement varies considerably among those countries. In most countries, programming specific frequencies into a scanner counts as intentional listening. In the UK you can openly listen to air traffic control without problems, even though this is not officially allowed. Listening to police communication is a different matter, especially if you draw their attention by regularly appearing first at the location of an accident. In France on the other hand, your scanner will probably be confiscated and you will get a large fine if the authorities find any non-amateur, non-broadcast frequency programmed in it. Anyway, you are unlikely to be caught if you use a scanner only at home and keep silent about it.
In the USA, many states restrict mobile or portable use of scanners, while use at home is generally allowed. However it is illegal to monitor telephone communications (cordless or mobile) and certain other types of transmissions.
See you next time when we discuss the FM broadcast band.
The Netherlands does have a 4m amateur band from 70 to 70.5MHz now. As opposed to the 6m band, there are only a very few commercially made amateur transceivers for this band. For FM most hams use old professional mobile radios, for SSB and CW, they mostly use a transverter, a box that converts the signal to and from a transceiver for another band (typically 10m) both ways, from 10m to 4m on transmission, from 4m to 10m on reception.
I added a band diagram. In the summer of 2014 I finally got the pleasure of picking up some OIRT FM stations (around 67MHz) on my own wideband receiver, using only its telescopic whip antenna.