The VHF starts at 30MHz. Wavelengths are less than 10 meters. This is the lowest VHF band. Long distance communication is sufficiently rare and unreliable, that it is considered useless for professional users.
It is a rather unpopular band, at least for professional users. This is caused by the following:
Analog voice communication on VHF is mainly in FM, sometimes in AM. Above 30MHz, SSB is never used, except by radio amateurs who use it on their bands up to 10GHz.
In some countries this band is or was widely used for mobile radio communication, such as taxis, police etc. This was the case in the USA, but also in Germany and France. In The Netherlands this was not the case. In Germany this band is called the 8 meter band. In the USA this band is on almost every scanner, but in The Netherlands this band is only on the more expensive scanners.
This part of the spectrum is widely used by low power applications, such as cordless microphones, cordless telephones and radio controlled aircraft. Radio controlled aircraft have different frequency bands from radio controlled cars and boats, as the consequences of losing control of a model aircraft are usually much greater. Radio controlled cars and their remote control transmitters (often in the 27MHz band) are sold as toys for children, while model aircraft are for more serious hobbyists. In Europe the 35MHz band is used for model aircraft and the 40MHz band is used for both model aircraft and for ground-based models.
In the USA, cordless phones transmit in the bands 43.72-44.48MHz (channels 1-15 on base sets), 46.61-46.97MHz (channels 16-25, old channels 1-10 on base sets and 48.76-49.99MHz (channels 1-25 on handsets). As opposed to most duplex radio systems, there is no fixed offset between the corresponding base and handset channels. The cordless phone bands were also used by baby monitors and toy walkie talkies, These phones were often imported into Europe, but their use (and even possession) was illegal. One reason given was that they could potentially interfere with aircraft communications. A strange argument though, because Europe uses the same aircraft band as the USA and in the USA there are also large airports in densely populated areas. Europe developed its own low VHF cordless phone standard, called CT0. They used 12 channels (base sets from 31.0375 to 31.3125MHz, handsets from 39.9375 to 40.2125MHz).
Listening to cordless phones with a scanner is illegal in the USA and most other countries, but not in The Netherlands. When you do listen to these phones, it is sufficient to monitor the base channels only; the handset signal is audible on those frequencies as well. In 1995 I sometimes monitored the CT0 band with a scanner and this band was very busy in my apartment block. Cordless phones in both Europe and the USA moved to higher bands and are now almost exclusively digital. Some older phones are still in use though.
The low VHF band is used by the military worldwide. The military in The Netherlands have (or had) portable transceivers capable of transmitting in FM on any frequency between 30 and 88MHz. These sets are now available on the surplus market. Apparently they use any frequency they see fit and that does not interfere with other users. At least for voice communication they do not use encryption most of the time. By using short transmissions, low power and unpredictable frequencies, they reduce the chance that the enemy (or radio hobbyists) intercept their transmissions.
In the 1930s, the 5m amateur band (around 59MHz) was available in Europe and in the USA. In the late 1980s (when 6m was introduced in The Netherlands), some old amateurs told about the fond memories they had about the old 5m band. I guess they have died out now. After World War II, the 5m band was taken away from radio amateurs to give way to VHF television channels. In the USA they got the 6m ham band (50-54MHz) in return, but not so in Europe. In the UK they got 4m instead.
The UK was the first European country to get the 6m in the mid 1980s when they switched off their old 405-line TV service on VHF. The 6m band occupies part of TV channel 2 in Europe, but this channel was very unpopular among TV station operators. Remember that consumer oriented literature refers to sporadic E conditions as extremely bad conditions. In the late 1980s, The Netherlands authorized use of the 6m band between 50 and 50.45MHz with a special permit. Later the band became a regular amateur band and in most European countries it runs from 50 to 52MHz. However, The Netherlands has some restrictions on this band, the most important one is that split frequency operation is prohibited. So 6m repeaters are not allowed in The Netherlands.
The 6m amateur band is often called the "magic band", as many propagation modes are available on it. The surprise factor that is mostly loathed by professional users, is loved by amateurs. Although the 6m band is a VHF band, F2 layer propagation (as on shortwave) is still possible. Worldwide communication is sometimes possible on this band.
They E-layer in the ionosphere is of lesser importance to shortwave propagation, but it plays a key role on VHF. Solar radiation sometimes creates very dense patches of ionization in this layer, against which radio waves in the VHF range can reflect. This is called sporadic E propagation, which allows a range of 1500-2000km. This mode of propagation starts at 20MHz and extends to 200MHz and beyond. However, on 50MHz this condition can hardly be called sporadic. It occurs on many days during the summer season and on some winter days as well.
When small pieces of rock (a few millimeters to a few centimeters across) enter the atmosphere, they get vaporized by the friction against the air and this generates intense ionization. This patch of ionized air caused by a meteor can be used as a reflector for radio waves and this mode of propagation works very well on 6m. This meteor scatter tends to severely distort the signals, so it is best suited for CW morse telegraphy.
On this band, as with other VHF and UHF amateur bands, SSB is mostly used for long distance voice communication and FM for local communication, including repeaters.
The earliest television systems in 1928 used video signals of only 30 lines per frame and 10 frames per second. This required a video bandwidth of around 5kHz, so it could be transmitted on mediumwave. When the mechanical systems with rotating disks were replaced by fully electronic systems with CRT tubes, the number of lines per frame and the number of frames per second could be increased dramatically. In England they used a system with 405 lines and 25 full frames (transmitted as 50 interlaced half frames) per second. The required video bandwidth is around 2.5MHz, which is 500 times as much as for the old system. The first TV transmitter was using AM modulation, so it required a bandwidth of around 5MHz.
In 1936 the BBC started its television transmissions around 40MHz, using a 405-line system. Engineers at Bell Labs in New York once received such a transmission and filmed it. This is the only preserved footage of pre-war British television. At that time the video signal was AM modulated. The sound channel was also AM modulated on a nearby frequency. After World War II, AM modulation was replaced by VSB (Vestigial Sideband). All terrestrial (non-satellite) analog TV systems use VSB. In this mode a single sideband is transmitted, as well as the carrier and part of the other sideband. Instead of 5MHz, the signal only occupies around 3MHz of bandwidth. It can still be detected by an ordinary AM detector. Because of the low bandwidth of the 405 line system and the low frequencies of these channels, British TV has been received literally around the globe.
After World War II, there were were several mutually incompatible analog TV standards in use in Europe. The UK and Ireland used the 405 line system. In the late 1960s this got displaced by the 625-line system in the UHF band, the 405 line system was abolished in the mid 1980s. France used an 819-line system, which also got displaced by a 625-line system in the late 1960s, the 819-line system was abolished around 1980. Most other countries used the 625-line system. The 625-line system used channels of 7MHz wide, while the 405-line system used narrower channels and the 819-line system used channels of more than 10MHz wide.
Until the 1970s, Belgium used an 819-line system for its French language service (but with narrower channels than France) and a 625-line system for its Dutch language service (but with positive video modulation and AM sound, whereas The Netherlands used negative video modulation and FM sound). So Belgium used two standards, which were not compatible with any neighboring country. In Belgium and the southern part of The Netherlands, multi-standard TV sets were widely available. If your hobby was TV-DX, such a multi-standard TV set was a must-have, but then you did not have the 405-line British standard yet. Contrast this with North America, which used a single 525-line standard.
In Europe, TV band I runs from 41 to 68MHz. The lowest TV channel in the standard band plan (channel 2) runs from 47 to 54MHz. The part of the band between 41 and 47MHz was too narrow for a complete channel, but this was used by some countries with different channel plans. So neither Europe nor America have a channel 1 in their TV band plans.
Before 1945, the FM broadcast band in the USA ran from 42 to 48MHz. Apparently there are still occasional transmissions on this band a few times per year, so you can hear something on an antique FM radio.
Radio astronomy is a use of the spectrum not yet encountered. Most of it occurs on much higher frequencies and some bands have been reserved for it. All transmitters on earth are prohibited from using these reserved bands, so radio astronomers can hear faint signals from space Some of these signals originate from billions of light years away, so they were originally emitted billions of years ago.
Recently the Low Frequency Array (LOFAR ) was built, which is a radio telescope consisting of thousands of small radio receivers with small antennas, spread out over an area of thousands of kilometers across. A large set of such LOFAR receivers is located in the province of Drenthe in The Netherlands. Signals from all these receivers are sent to a huge computer, where they are combined into an image of the Universe. LOFAR monitors the spectrum between 10 and 250MHz, which corresponds to wavelengths between 1.2 and 30 meters. Each receiver has a low band antenna (mainly sensitive to signals between 30 and 80MHz) and a high band antenna (mainly sensitive to signals between 120 and 240MHz). The spectrum monitored by LOFAR is not allocated to radio astronomy, so they have to tolerate any land based transmissions that happen to be there. That's why the FM broadcast band is excluded from LOFAR beforehand. Any attempt to extract signals from distant galaxies in this band would be futile.
Receivers for the VHF band are different from shortwave receivers. Using a manually tuned receiver for non-broadcast reception is not very satisfying. This is because transmissions tend to be very brief and they mostly stop just when you managed to tune the radio to them. You can hear a single channel, which is silent most of the time. When you tune manually across the band hunting for active channels, you arrive at them late most of the time. Manual tuning does have its place for long-distance reception (DX) though, so you can find unexpected stations.
In the 1960s and before, some professional VHF monitoring receivers were produced with analog tuning. It is impossible to find out the exact frequency of a received station, because their bands are much too wide (20MHz and more). Today some toy radios with extensive VHF coverage are still produced, but they are pretty much useless (cramming the entire range 108-174MHz into a single dial of 5cm in length). I guess these radios are mainly sold in countries where scanners are prohibited and these toy radios are sufficiently harmless so they are tolerated by the authorities,
Hobbyists mostly use low cost scanners to listen to mobile communication on the VHF and UHF bands. Most scanners can only receive FM (and sometimes AM modulated signals) on fixed channels (multiples of 5 or 12.5kHz) in limited frequency ranges. More expensive VHF/UHF receivers exists, which cover the entire VHF and UHF spectrum, have a tuning knob in addition to the scanning facilities, and can receive SSB (useful on the amateur bands only). The ICOM IC-R7000 could receive the entire range from 25MHz to 2GHz.
In 1989 the ICOM IC-R9000 was introduced. It could receive anything between 100kHz and 2GHz and performed well across the range, on shortwave as well as on VHF and UHF. With it s price tag of more than 12000 guilders, it was comfortably out of range of my budget. At that time, digital voice communications hardly existed, so you could receive pretty much every voice communication transmitted over the airwaves, from broadcast television to mobile telephones, from shortwave amateurs to the local police. Therefore this radio was a true everything-receiver. Although receivers with similar capabilities are now within my budget, there are so many things they cannot receive, such as DAB, mobile phones and police communications, because they are all digital. This type of radios are sometimes called DC to daylight receivers and those that have good shortwave performance, are still very expensive.
See you next time when we discuss the rest of the low VHF bands.
I added a band diagram.