USA: Birthplace of CB radio

After the end of World War II, there was a great international interest in the civilian applications of radio technology and electronics. Many who had served as soldiers had come into contact with so-called transceivers. These radio systems, primarily designed for portable use and therefore relatively compact, combined the transmitter and receiver in a single device. Designed for voice communication, they automatically transmitted on the same frequency to which the receiver was tuned. This was made possible by a direct-wave receiver built with a single vacuum tube, which could also be operated as a single-stage transmitter via a multi-pole switch. Thus, one and the same resonant circuit determined the operating frequency for both receiving and transmitting. The amplifier for the earpiece, equipped with another vacuum tube, served as a modulator during transmission.

Since the devices were easy to operate even for laypersons, a much less extensive briefing sufficed instead of comprehensive training for a radio officer. Essentially, this involved mounting or extending the antenna, ensuring a power supply, setting the operating frequency, and pressing the designated switch to transmit. Unlike shortwave radios, these devices were designed for short-range communication and therefore mostly operated in the lower VHF frequency range up to about 52 MHz, and sometimes even in the upper shortwave range. By the late 1930s, the US military had been equipped with such devices on a large scale. The BC222 model, which was worn like a backpack, became widely used there.

Due to its simple operating principle, such devices were also ideally suited for home construction. After the war, amateur radio magazines published numerous articles with circuit diagrams and construction descriptions for devices built in this way. In most cases, the basic concept of the BC222 was adopted and adapted to components available to amateurs. Initially, the devices were designed for the 10-meter or 6-meter bands. With the advent of television sets, components suitable for the UHF range, in particular, soon became available, enabling inexpensive construction for frequencies extending into the UHF range. Instead of a conventional resonant circuit, the transceiver circuit now used an easily replicated tube or pot circuit. The simple construction of such transceivers practically invited hobbyists without an amateur radio license to build such devices for almost any frequency from about 25 MHz to over 500 MHz and to operate them without authorization outside of amateur radio bands.

Technologically, all the prerequisites were already in place to offer industrially manufactured transceivers at a price affordable for everyone. Due to the sparsely populated areas outside of metropolitan areas, which mostly lacked access to any telephone networks, there was considerable interest in the new wireless communication possibilities in the USA. Clubs and societies were founded with the goal of establishing a "citizens radio" system. Since compact antennas could be used and interference was less of a concern, there were many advocates for setting up such a system in the UHF band. This was countered by the disadvantage of shorter ranges within line of sight. In fact, devices operating in the 460 to 470 MHz range were officially permitted in the USA from 1948 onwards. These devices were categorized into two approval classes, A and B. For most private individuals, only the simpler UHF radios were affordable. With the rapidly increasing number of stations, the simple technology used here, primarily due to the poor selectivity of the mostly superregenerative single-circuit receivers, soon became inadequate. To conduct multiple radio conversations simultaneously within a narrow frequency band, superheterodyne receivers were needed. While these were certainly feasible for the wavelengths used (around 70 centimeters), they were still quite complex to manufacture at the time, which explained the high prices of truly usable devices. At the same time, the UHF band was becoming increasingly attractive to professional users. It was therefore becoming clear that the more sophisticated devices would prevail and commercial users would displace private users.

For citizens radio, interest in UHF equipment waned due to the anticipated higher purchase costs without any significant increase in range. A similar technology to that used by shortwave amateurs found greater favor. This led to the official introduction in 1958 of the 27 MHz Class D radios, and thus to what we know today as CB radio. Radios for this frequency range could be manufactured primarily using components intended for medium and shortwave broadcast receivers *). Therefore, the widespread use of superheterodyne receivers no longer posed a major obstacle. Furthermore, many audio output tubes were still perfectly usable for transmitter output stages in the 27 MHz range. Consequently, powerful radios could be offered at significantly lower prices. As a result, 23 channels were allocated for CB radio in this frequency range. Even then, these corresponded in frequency to our current CB channels 1 to 23:

Since the prescribed transmission frequencies of the 27 MHz channels had to be adhered to with high precision due to licensing regulations, there was no alternative to operating the transmitters with crystal oscillators. The significantly smaller bandwidth of the superheterodyne receivers and the 10 kilohertz channel spacing also made high accuracy of the transmission frequency crucial. However, the necessary crystals were very expensive. Initially, hardly anyone considered using radios capable of transmitting on all 23 channels. At that time, two-way radios were heavy devices entirely equipped with vacuum tubes. The superheterodyne receivers built into these devices were continuously tunable in many of the CB radios initially available. The receiving frequency could therefore be set with a tuning knob, just like on an old broadcast receiver, and at least within the range of 26.96 to 27.26 MHz. Thus, one could receive all 23 channels without needing crystal oscillators. Many CB radios had a transmitter with five, sometimes six, crystal slots, allowing the user to switch between the corresponding number of transmission channels using a rotary switch on the front panel. Equipping all the slots with crystals required an investment roughly equivalent to that of a complete older radio with a superregenerative receiver. The less convenient newer 27 MHz radios had only one crystal socket located on the front panel. To change the transmission frequency, the appropriate crystal was simply inserted into the socket. To tune the receiver to the user's own transmission frequency, radios with continuously variable tuning usually had a switch labeled "Spot." This switch only activated the transmitter's oscillator; the transmitter's output stage remained de-energized. This prevented any transmission, allowing the user to find the correct point on their receiver's tuning dial to tune to the same channel on which they were transmitting.

Many of the radios offered at the time were equipped with a mechanical chopper. This periodically reversed the polarity of a connected DC voltage in the low-voltage range to transform the resulting AC voltage up. Equipped in this way, the devices were not dependent on the 117-volt AC mains supply but could also be operated on board vehicles or in remote areas without AC power using batteries. The new CB radio system was not only popular with people who were simply fascinated by the technology. Because the devices could also be used in vehicles, this new means of communication was very attractive to farmers, foresters, tradespeople, fishermen, and especially truck drivers. However, the rather cumbersome operation with spot switches and separate receiver tuning proved problematic while driving. Some manufacturers therefore equipped their devices with additional crystal slots for fixed receiver frequencies. Most users, however, did not want to forgo their tunable receiver, at least when operating from a stationary position. However, it also offered the possibility of communicating with stations that did not have the same transmitting crystals by transmitting on different frequencies and tuning the receivers accordingly. With the rapidly increasing congestion of CB frequencies, the advantage of being able to tune the receiver slightly off the actual channel frequency to reduce interference from adjacent channels was also appreciated. This practice among American CB radio operators is likely the main reason why many later US radios were equipped with a so-called "delta tune" control or switch for fine-tuning the receiver. Simpler five-channel radios, in which the receiver could only be operated via crystal control and lacked a tuning option, were initially only of interest if communication was to take place on fixed, pre-assigned channels. Due to their smaller dimensions, however, these radios were easier to mount in vehicles. They were therefore particularly popular with truck drivers, who mostly used channel 19 and only switched to the reserved channel 9 for emergency calls.

In the USA, until the early 1980s, users of CB radios required a personal license from the Federal Communications Commission (FCC). They were granted considerable freedom regarding the equipment they used. However, fundamental rules, such as adhering to the then-maximum permissible transmit power of 3.5 watts, were enforced very strictly. Anyone using equipment capable of transmitting outside the 23 permitted channels faced severe penalties, as did users of so-called "afterburners" to increase transmit power. Regulations essentially only applied to the transmitters used. Provided the relevant rules were followed, stations similar to those of the amateur radio era, consisting of separate transmitters and receivers, could also be used. Products from the Browning and Demco brands were particularly widespread. These companies initially offered crystal-controlled 23-channel transmitters for AM modulation and matching receivers. As with the receivers included in many complete radio sets, this unit also featured a tuning knob for continuous frequency tuning via VFO. This allowed reception of all CB channels, and in some models, even the frequencies up to 27.595 MHz used in the USA at that time for business radio purposes. In addition to the power supply, the modulation amplifier was sometimes even a separate component in such radio systems. Later models were released that also enabled operation in SSB modulation mode. The FCC requirement stipulated that the PEP power must not exceed 12 watts.

Around 1960, the transistor, invented only in 1948, became increasingly widespread in radio technology. Consequently, transistors were also used more and more frequently in CB radios, though initially only in the receiver. While suitable transistors for the audio frequency (AF) output stage, which in CB radios was usually also used as a modulator, were quickly found in the product ranges of the semiconductor industry, the production of power transistors for transmitters initially presented greater difficulties. Thus, there were initially devices in which the receiver and the modulation amplifier were already transistorized, but the transmitter still used vacuum tubes. Meanwhile, miniature vacuum tubes developed for battery operation with lower operating voltages and lower power consumption became available. This made portable CB radios with high-quality superheterodyne receivers possible, with smaller dimensions and less weight than the early transceivers with superregenerative receivers. Some of these devices were also equipped with a roadcast receiver section.

Initially, there was considerable skepticism among CB radio users in the USA regarding the new transistor devices. Only handheld radios, which could not be manufactured as small and lightweight using vacuum tubes, found wider acceptance. However, with the increasing spread of transistor technology, Japanese-made devices rapidly captured market share, first in transistor radios and soon in the field of radio technology as well. At first, very simple handheld radios came from Japan, but mobile and base station radios, as well as more sophisticated handheld models, soon followed. Even before World War II, Japan had been a technologically advanced country, particularly in the field of radio technology. Severely damaged by the atomic bombings, the country focused entirely on the production of goods for civilian use after the war, and especially on the export of technical products. While CB radios had previously been manufactured almost exclusively in the USA, domestic manufacturers sought collaborations with Japanese manufacturers, primarily due to lower labor costs, to increasingly have their devices produced there. It took barely a decade before CB radios of Japanese origin dominated the US market in the first half of the 1970s.

*) In the USA there was no longwave radio broadcasting; FM radio broadcasting was of little importance at that time.

Circuit diagrams of typical CB radios from the USA up to the early 1970s