Misplaced Pages

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53-649: The original Bell System US and Canadian mobile telephone system includes three frequency bands, VHF Low (35-44 MHz, 9 channels), VHF High (152-158 MHz, 11 channels in the U.S., 13 channels in Canada), and UHF (454-460 MHz, 12 channels). Alternative names were "Low Band", "High band" and "UHF". In addition to the Bell system ( wireline incumbent ) channels, another 7 channels at VHF, and 12 channels at UHF were granted to non-wireline companies designated as "RCCs" (Radio Common Carriers). These RCC channels were adjacent to

106-505: A DTMF (dual tone multi-frequency) keypad attached on the front panel, which fooled the terminal into believing an IMTS mobile was using the system. These units were not very common or practical because they lacked the power to reliably connect to the base station over the distances common in the IMTS systems. A compromise existed with the briefcase phone, which had somewhat higher power in the range of 10 to 20 watts (depending on how much battery

159-415: A cradle with a direct dialing keyboard. These looked and functioned much like a landline, or hardwired, telephone. Unlike cellular handsets, these units passed through a dial tone when the receiver was lifted from the cradle and in this way seemed more like a landline telephone. There was a separate large radio transceiver chassis, typically measuring at least a foot square and 6 inches high, mounted either in

212-478: A dipole, or a quarter-wave whip with an adequate size ground plane. Whips not mounted on the radio itself are usually fed with coaxial cable feedline of 50 ohm or 75 ohm impedance. In transmitting antennas the impedance of the antenna must be matched to the feedline for maximum power transfer. A half wave whip antenna (length of 1 2 λ {\displaystyle {\tfrac {1}{2}}\lambda } ) has somewhat higher gain than

265-408: A flexible fiberglass rod around a wire core and can be up to 11 m (35 feet) long. The length of a whip antenna is determined by the wavelength of the radio waves it is used with. Their length varies from compact electrically short antennas ⁠ 1 / 10  ⁠  wavelength long, up to ⁠ 5  / 8 ⁠   wavelength to improve directivity. The most common type

318-404: A form of monopole antenna . The antenna is designed to be flexible so that it does not break easily, and the name is derived from the whip -like motion that it exhibits when disturbed. Whip antennas for portable radios are often made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. Longer whips, made for mounting on vehicles and structures, are made of

371-399: A large amount of power (10 to 15 amperes at 12 volts) and this was supplied by thick power cabling connected directly to the automobile's battery. It therefore was quite possible and not uncommon for an IMTS telephone to drain an automobile's battery if used for moderate periods of time without the automobile engine running or if left on overnight. Optionally these units were also connected to

424-441: A quarter wave ground plane antenna with horizontal ground wires is around 22 ohms, a poor match to coaxial cable feedline, and the main lobe of the radiation pattern is still tilted up toward the sky. Often (see pictures) the ground plane rods are sloped downward at a 45-degree angle, which has the effect of lowering the main lobe of the radiation pattern so more of the power is radiated in horizontal directions, and increases

477-416: A quarter wave whip, but it has a current node at its feedpoint at the base of the rod so it has very high input impedance. If it was infinitely thin the antenna would have an infinite input impedance, but the finite width gives typical, practical half wave whips an impedance of 800–1,500 ohms. These are usually fed through an impedance matching transformer or a quarter wave stub matching section (e.g.

530-462: A quarter-wavelength long connected to the opposite side of the feedline, extending horizontally from the base of the whip, is often used. This is called a ground plane antenna . These few short wire elements serve to receive the displacement current from the driven element and return it to the ground conductor of the transmission line, making the antenna behave somewhat as if it has a continuous conducting plane under it. The radiation resistance of

583-403: A quarter-wavelength, and still be resonant , by cancelling out the capacitive reactance of the short antenna. This is called an electrically short whip . The coil is added at the base of the whip (called a base-loaded whip) or occasionally in the middle (center-loaded whip). In the most widely used form, the rubber ducky antenna , the loading coil is integrated with the antenna itself by making

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636-423: A specified geographic area. In Canada , ILECs are the original telephone companies such as Telus ( BC Tel and Alberta Government Telephones ), SaskTel , Manitoba Telecom Services (MTS Allstream), Bell Canada and Aliant , as well as any other company that previously held a monopoly to serve a community and continues to do so, or a successor company if it is bought and absorbed. ILECs are obligated to serve

689-455: Is approximately one-quarter of the wavelength ( 1 4 λ {\displaystyle {\tfrac {1}{4}}\lambda } ), called a "quarter-wave whip" (although often shortened by the use of a loading coil ; see Electrically short whips below). For example, the common quarter-wave whip antennas used on FM radios in the USA are approximately 75 cm (2.5 feet) long, which

742-404: Is never approached in actual antennas unless the ground plane is many wavelengths in diameter. 2 dBi is more typical for a whip with a ground plane of 1 2 λ   . {\displaystyle {\tfrac {1}{2}}\lambda ~.} Whips mounted on vehicles use the metal skin of the vehicle as a ground plane. In hand-held devices usually no explicit ground plane

795-449: Is possible with coils at about one-half or one-third and two-thirds that do not affect the aerial much at the lowest band, but it creates the effect of stacked dipoles at a higher band (usually ×2 or ×3 frequency). At higher frequencies the feed coax can go up the centre of a tube. The insulated junction of the tube and whip is fed from the coax and the lower tube end where coax cable enters has an insulated mount. This kind of vertical whip

848-426: Is provided, and the ground side of the antenna's feed line is just connected to the ground (common) on the device's circuit board. Therefore, the radio itself serves as a rudimentary ground plane. If the radio chassis is not a good deal larger than the antenna itself, the combination of whip and radio functions more as an asymmetrical dipole antenna than as a monopole antenna . The gain will be somewhat lower than

901-463: Is roughly one-quarter the length of radio waves in the FM radio band, which are 2.78 to 3.41 m (9 to 11 feet) long. Half-wave whips ( 1 2 λ {\displaystyle {\tfrac {1}{2}}\lambda } long) which have greater gain , and five-eighth wave whips ( 5 8 λ {\displaystyle {\tfrac {5}{8}}\lambda } long) which have

954-470: Is split into a horizontal lobe and a small second lobe at a 60° angle, so high angle radiation is poor. The input impedance is around 40 ohms. In a whip antenna not mounted on a conductive surface, such as one mounted on a mast, the lack of reflected radio waves from the ground plane causes the lobe of the radiation pattern to be tilted up toward the sky so less power is radiated in horizontal directions, undesirable for terrestrial communication. Also

1007-411: Is the quarter-wave whip , which is approximately ⁠ 1  / 4 ⁠ wavelength long. Whips are the most common type of monopole antenna , and are used in the higher frequency HF , VHF and UHF radio bands. They are widely used as the antennas for hand-held radios, cordless phones , walkie-talkies , FM radios , boom boxes , and Wi-Fi enabled devices, and are attached to vehicles as

1060-451: The J-pole antenna ). An advantage is that because it acts as a dipole it does not need a ground plane. The maximum horizontal gain of a monopole antenna is achieved at a length of five eighths of a wavelength 5 8 λ {\displaystyle {\tfrac {5}{8}}\lambda } so this is also a popular length for whips. However at this length the radiation pattern

1113-549: The electric field vertical and the magnetic field horizontal. Vertical whip antennas are widely used for nondirectional radio communication on the surface of the Earth, where the direction to the transmitter (or the receiver) is unknown or constantly changing, for example in portable FM radio receivers, walkie-talkies , and two-way radios in vehicles. This is because they transmit (or receive) equally well in all horizontal directions, while radiating little radio energy up into

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1166-490: The Bell System frequencies. RCCs were also allowed to offer paging services to "beepers" or " pagers " on a secondary basis on the same channels, but soon, with the growth of paging, RCC mobile phone services were given lower priority. Some RCCs utilized IMTS technology, but most adopted the "Secode-2805" system which allowed for simultaneous paging, so after a few years, the predominant provider of mobile telephone service

1219-639: The MTS, or manual mode. The "Z" channels were sold at auction by the FCC in approximately 2003 to other services and remain largely unused. The VHF and UHF frequencies have been opened to other services unrelated to mobile telephony and largely reassigned. The two VHF high-band channels designated JJ and JW were used only in Canada, and were not available for use in the United States. IMTS technology severely limited

1272-462: The MTS/IMTS service to be withdrawn. Increasing affordability of satellite service, and government investment in cellular expansion allowed MTS and IMTS to be removed. Wireline incumbent An incumbent local exchange carrier ( ILEC ) is a local telephone company which held the regional monopoly on landline service before the market was opened to competitive local exchange carriers , or

1325-467: The Motorola TLD-1100 series, used two circuit boards about 8 inches square, to perform the channel scanning and digit decoding process, and all logic was performed with discrete transistors. In a given city, one IMTS base station channel was "marked idle" by the transmission of a steady 2000 Hz "idle" tone. Mobiles would scan the available frequencies and lock on to the channel transmitting

1378-436: The addition of rudimentary parity checking. Digits are formed with a pulsetrain of alternating tones, either connect and silence (for odd digits) or connect and guard (for even digits). When the base station received the calling party's identification, it would send dialtone to the mobile. The user would then use the rotary dial, which would send the dialed digits as an alternating 10 pps pulse train (originally, directly formed by

1431-458: The antenna's axis), with the radiated power falling off with elevation angle to zero on the antenna's axis. Whip antennas less than one-half wavelength long, including the common quarter wave whip, have a single main lobe , and with a perfectly conducting ground plane under it maximum field strength is in horizontal directions, falling monotonically to zero on the axis. With a small or imperfectly conducting ground plane or no ground plane under it,

1484-462: The antennas for car radios and two-way radios for wheeled vehicles and for aircraft. Larger versions mounted on roofs, balconies and radio masts are used as base station antennas for amateur radio and police, fire, ambulance, taxi, and other vehicle dispatchers. The whip antenna is a monopole antenna , and like a vertical dipole has an omnidirectional radiation pattern , radiating equal radio power in all azimuthal directions (perpendicular to

1537-446: The area covered by one tower (a "cell") and increasing the number of cells. The disadvantage of this is more towers are required to cover a given area. Thus, IMTS and MTS systems still exist in some remote areas, as it may be the only feasible way to cover a large sparsely-populated area. The basic operation of IMTS was very advanced for its time, considering that integrated circuits were not commonly available. The most common IMTS phone,

1590-411: The call was for someone else would resume scanning for mark idle tone, while the called mobile would then transmit 2150 Hz "guard" tone back to the base station. This would also initiate ringing at the mobile, and when the mobile subscriber picked up the phone, 1633 Hz "connect" tone would be sent back to the base station to indicate answer supervision and the voice path would be cut through. When

1643-402: The car's horn and could honk the horn as a ringer to summon a user who was away from the car. The IMTS units were full duplex , meaning that a user could both talk and hear the other party at the same time. This was an improvement over the earlier MTS systems, most of which were half duplex , allowing only one party to transmit at a time; the user had to "push to talk" to speak and then "unkey"

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1696-461: The corporate successor of such a firm. An incumbent local exchange carrier is a local exchange carrier (LEC) in a specific area that The Federal Communications Commission (FCC) may, by rule, provide for the treatment of an LEC (or class or category thereof) as an ILEC if: ILECs have the same duties as a LEC and in addition: In the United States , ILECs were companies in existence at

1749-632: The earpiece. Two lights on the "head" indicated busy (red) if no channels were idle and in-use (green) if connected to the tower, or depressing the push-to-talk switch. There was no encryption and all conversations were public. The frequencies listed below (in MHz) are those formerly used in the US & Canadian Mobile Telephone Service and the Improved Mobile Telephone Service. The low band "Z" prefixed channels were always operated in

1802-400: The entire exchange area as a "provider of last resort", while CLECs can choose which locations to serve, be it by facilities of their own or by resale of services of an ILEC or another CLEC. Whip antenna A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver or transmitter . A whip antenna is

1855-402: The exclusive use of a channel for the duration. Because of this limitation these systems had a much lower capacity than cellular systems and all channels busy conditions were common. In larger cities this dictated a very limited number of simultaneous calls. Each subscriber was given a packet of dialing and use instructions. Roaming (receiving calls out of the "home area") was achieved by selecting

1908-424: The general result is to tilt the main lobe up so maximum power is no longer radiated horizontally but at an angle into the sky. Antennas longer than a half-wavelength have patterns consisting of several conical "lobes"; with radiation maxima at several elevation angles; the longer the electrical length of the antenna, the more lobes the pattern has. A vertical whip radiates vertically polarized radio waves, with

1961-532: The idle tone. When a call was placed to a mobile, the idle tone would change to 1800 Hz "channel seize" tone (the idle tone would appear on another frequency, if available), and the 7 digit mobile number (three digits of the NPA and the last four digits of subscriber number, the NXX was not sent) would be sent out as rotary dial pulses, switching between 2000 and 1800 Hz to represent digits. Any mobile recognizing that

2014-413: The input impedance for a good match to standard 50-ohm coaxial cable . To match 75-ohm coaxial cable, the ends of the ground plane can be turned downward or a folded monopole driven element can be used. To reduce the length of a whip antenna to make it less cumbersome, an inductor ( loading coil ) is often added in series with it. This allows the antenna to be made much shorter than the normal length of

2067-462: The maximum horizontal gain achievable by a monopole, are also common lengths. The gain and input impedance of the antenna is dependent on the length of the whip element, compared to a wavelength, but also on the size and shape of the ground plane used (if any). A quarter wave vertical antenna working against a perfectly conducting, infinite ground will have a gain of 5.19  dBi and a radiation resistance of about 36.8  ohms . However this gain

2120-477: The mobile hung up, a burst of alternating 1336 "disconnect" and 1800 Hz "seize" tones would be sent to allow the base station to service another call. Mobiles would originate calls by sending a burst of connect tone, to which the base station responded with a burst of seize tone. The mobile would then respond with its identification, consisting of its area code and last four digits of the phone number sent at 20 pulses per second, just as in inward dialing but with

2173-493: The mobile units were therefore very expensive ($ 2,000 to $ 4,000). Prior to the divestiture of AT&T in 1984, Bell System IMTS subscribers usually leased the equipment at a monthly rate of up to $ 120. Availability of the channels was scarce hence airtime was also quite expensive at $ 0.70-1.20 per minute. Following the divestiture, customer-owned equipment was required by Bell companies and monthly rates then typically ran to $ 25 plus air time. Also, since there were so few channels, it

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2226-400: The rotary dial) of connect and guard tones. IMTS systems typically had 25 watts of transmitter power at the mobile station and 100-250 Watts at the terminal — unlike the newer cellular car telephones that had maximum power output of 3 watts and modern cellular handsets with power outputs of 0.6 watts. Mobile installations normally consisted of a "head unit" or the telephone handset which sat in

2279-407: The sky where it is wasted. Whip antennas are normally designed as resonant antennas; the rod acts as a resonator for radio waves, with standing waves of voltage and current reflected back and forth from its ends. Therefore, the length of the antenna rod is determined by the wavelength ( λ {\displaystyle \lambda } ) of the radio waves used. The most common length

2332-411: The specific channels used by the tower and service provider the user was traveling in and dialing a three-digit code, thereby logging the user's land number at that location. This process had to be repeated at each tower which, as noted, usually had a range of 40–60 miles. Some areas only had half-duplex (one-way) communications and required the push-to-talk switch in the handset, between the mouthpiece and

2385-551: The time of the breakup of AT&T into the Regional Bell Operating Companies (RBOCs), also known as the "Baby Bells". Various regional independents also held incumbent monopolies in their respective regions. The largest of these was GTE , the second largest ILEC after the Bell System. GTE was later absorbed into Verizon , an RBOC . In some areas, an independent telephone company is responsible for providing local telephone exchange services in

2438-462: The total number of subscribers. In the 1970s and the early 1980s, before the introduction of cellular phones, there were "waiting lists" of up to three years for those wishing to have mobile telephone service. These potential subscribers were waiting for other subscribers to disconnect their subscription in order to obtain a mobile telephone number and mobile phone service. These limitations resulted in low quantity sales and production of IMTS phones and

2491-445: The transmitter to hear the other party on the line. In 1960 General Electric introduced the "Progress Line" DTO- series MTS mobiles which were full duplex, although subscribers were still required to press the "push to talk" bar on the handset to speak. There were also IMTS handheld transceivers (Yaesu's 1982 vintage Traveler) that operated on 2-4 watts, and these were all half duplex. These were essentially modified "walkie-talkies" with

2544-564: The trunk or under the seats of an automobile. These transceivers were connected to the handset cradle with a multi-conductor cable usually around .5 inch thick. The mobile antennas almost always required a hole to be drilled in the body of the car to mount the antenna in; until the 1970s there were no "on-glass" antennas - these were developed later for the cellular car-mounted telephones. These whip antennas looked much like those used for CB radios and were about 19 in. long (1/4 wavelength at 155 MHz). These mobile telephone systems required

2597-405: The unbalanced impedance of the monopole element causes RF currents in the supporting mast and on the outside of the ground shield conductor of the coaxial feedline, causing these structures to radiate radio waves, which usually has a deleterious effect on the radiation pattern. To prevent this, with stationary whips mounted on structures, an artificial "ground plane" consisting of three or four rods

2650-441: The whip out of a narrow helix of springy wire. The helix distributes the inductance along the antenna's length, improving the radiation pattern, and also makes it more flexible. Another alternative occasionally used to shorten the antenna is to add a "capacity hat", a metal screen or radiating wires, at the end. However all these electrically short whips have lower gain than a full-length quarter-wave whip. Multi-band operation

2703-460: Was common for the phones to "queue up" to use a channel and IMTS manufacturers competed for the speed with which the units would seize an available channel. The limit of customer numbers on MTS and IMTS was the driver for investment in cellular networks. In remote regions, this is not the case; in remote regions, obsolescence is the driver, but the lack of a suitable and affordable alternative has resulted in regulatory obstacles: customers did not want

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2756-540: Was in the briefcase), and which was full duplex. Typical IMTS briefcase phones were made by Canyon, GCS, SCM Melabs and Livermore Data Systems. IMTS base station sites generally covered an area 40–60 miles in diameter. This extended range was due to both their large transmitter power and in many cases higher antenna placement at anywhere from 100 to 500 ft. IMTS base stations in larger cities had as many as 7 or 8 channels while rural stations had as few as one or two channels. Each telephone conversation (connection) required

2809-537: Was the Bell System companies. A given provider might have offered service on one, two, or all three bands, although IMTS was never offered on low band (only MTS, but Whidbey Telephone in Washington State had a custom-designed direct-dial system.) These were prone to network congestion and interference since a radio closer to the terminal would sometimes take over the channel because of its stronger signal. Cellular networks remedied this problem by decreasing

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