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34-451: DirectBand used the 67.65 kHz subcarrier leased by Microsoft from commercial radio broadcasters. This subcarrier delivers about 12 kbit/s (net after ECC ) of data per tower, for over 100 MB per day per city. Data included traffic, sports, weather, stocks, news, movie times, calendar appointments, and local time. DirectBand did not use the RDS ( Radio Data System ) subcarrier. RDS

68-484: A carrier signal which is used to carry it through a telephone line , coaxial cable , or optical fiber . Demodulation was first used in radio receivers . In the wireless telegraphy radio systems used during the first 3 decades of radio (1884–1914) the transmitter did not communicate audio (sound) but transmitted information in the form of pulses of radio waves that represented text messages in Morse code . Therefore,

102-434: A radio reading service for the blind, which reads articles in local newspapers and sometimes magazines. The vision-impaired can request a special radio, permanently tuned to receive audio on a particular subcarrier frequency (usually 67 kHz or 92 kHz), from a particular FM station. Services like these and others on broadcast FM subcarriers are referred to as a Subsidiary Communications Authority (SCA) service by

136-421: A demodulator may represent sound (an analog audio signal ), images (an analog video signal ) or binary data (a digital signal ). These terms are traditionally used in connection with radio receivers , but many other systems use many kinds of demodulators. For example, in a modem , which is a contraction of the terms modulator /demodulator, a demodulator is used to extract a serial digital data stream from

170-538: A demodulator, if they pass the radio waves on nonlinearly . An AM signal encodes the information into the carrier wave by varying its amplitude in direct sympathy with the analogue signal to be sent. There are two methods used to demodulate AM signals : SSB is a form of AM in which the carrier is reduced or suppressed entirely , which require coherent demodulation. For further reading, see sideband . Frequency modulation (FM) has numerous advantages over AM such as better fidelity and noise immunity. However, it

204-533: A remote transmitter , often located in a difficult-to-access area at the top of a mountain. A station's engineer can carry a decoder around with them and know anything that's wrong, as long as the station is on the air and they are within range. This is the essence of a wireless transmitter/studio link . On wireless studio/transmitter links (STLs), not only are the broadcast station's subcarriers transmitted, but other remote control commands as well. Interruptible foldback , such as for remote broadcasting ,

238-424: A satellite transponder or microwave relay). Extra subcarriers are sometimes transmitted at around 7 or 8 MHz for extra audio (such as radio stations) or low-to-medium-speed data. This is referred to as multiple channel per carrier (MCPC). This is now mostly superseded by digital TV (usually DVB-S , DVB-S2 or another MPEG-2 -based system), where audio and video data are packaged together ( multiplexed ) in

272-431: A single MPEG transport stream . Demodulate Demodulation is extracting the original information-bearing signal from a carrier wave . A demodulator is an electronic circuit (or computer program in a software-defined radio ) that is used to recover the information content from the modulated carrier wave. There are many types of modulation so there are many types of demodulators. The signal output from

306-549: A station " format " name ALERT to automatically trigger radios to tune in for emergency info, even if a CD is playing. While it never really caught on in North America , European stations frequently rely on this system. An upgraded version is built into digital radio . xRDS is a system with which broadcasters can multiply the speed of data transmission in the FM channel by using further normal RDS subcarriers, shifted into

340-406: A variety of DirectBand receivers. All used a small (2.794 mm × 2.794 mm × 860 μm) radio receiver. Some designs added an ARM7 -based processor. The initial DirectBand products were a series of data watches. These had mild success, but never met expectations and production of new watches was discontinued in 2008. Recently, several other applications have surfaced, the most visible being

374-496: Is a different system and has much lower data rate (~730 bit/s after ECC, including framing). Its much narrower subcarrier is primarily used for radio station information and traffic. DirectBand and RDS can co-exist on the same FM station. Since many DirectBand uses were mobile, and there was no opportunity to request retransmission of a broadcast signal, DirectBand utilized an advanced error-correction strategy that allowed for reconstruction of messages even when sizable portions of

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408-520: Is also added at a 9% modulation to trigger radios to decode the stereo subcarrier, making FM stereo fully compatible with mono. Once the receiver demodulates the L+R and L−R signals, it adds the two signals ([L+R] + [L−R] = 2L) to get the left channel and subtracts ([L+R] − [L−R] = 2R) to get the right channel. Rather than having a local oscillator , the 19 kHz pilot tone provides an in-phase reference signal used to reconstruct

442-416: Is also possible over subcarriers, though its role is limited. Analog satellite television and terrestrial analog microwave relay communications rely on subcarriers transmitted with the video carrier on a satellite transponder or microwave channel for the audio channels of a video feed. There are usually at frequencies of 5.8, 6.2, or 6.8 MHz (the video carrier usually resides below 5 MHz on

476-437: Is much more complex to both modulate and demodulate a carrier wave with FM, and AM predates it by several decades. There are several common types of FM demodulators: QAM demodulation requires a coherent receiver. It uses two product detectors whose local reference signals are a quarter cycle apart in phase: one for the in-phase component and one for the quadrature component. The demodulator keeps these product detectors tuned to

510-458: The AM signal may be used for audio. Likewise, analog TV signals are transmitted with the black and white luminance part as the main signal, and the color chrominance as the subcarriers. A black and white TV simply ignores the extra information, as it has no decoder for it. To reduce the bandwidth of the color subcarriers, they are filtered to remove higher frequencies. This is made possible by

544-509: The DirectBand network. RDS uses a portion of the FM station spectrum immediately above the stereo signal, centered at 57 kHz (the stereo pilot frequency). RDS extends between about 55 and 59 kHz. DirectBand is above RDS, extending from about 59 kHz to 75 kHz. On October 26, 2009, Microsoft announced that MSN Direct service would end on January 1, 2012. Although this clearly indicated Microsoft's intent to cease usage of

578-748: The FCC in the United States , and as Subsidiary Communications Multiplex Operations (SCMO) by the Canadian Radio-television and Telecommunications Commission (CRTC) in Canada . The RDS / RBDS subcarrier (57 kHz) allows FM radios to display what station they are on, pick another frequency on the same network or with the same format, scroll brief messages like station slogans, news, weather, or traffic—even activate pagers or remote billboards. It can also broadcast EAS messages, and has

612-813: The base-band signal such as amplitude, frequency or phase are transmitted in the carrier signal. For example, for a signal modulated with a linear modulation like AM ( amplitude modulation ), we can use a synchronous detector . On the other hand, for a signal modulated with an angular modulation, we must use an FM ( frequency modulation ) demodulator or a PM ( phase modulation ) demodulator. Different kinds of circuits perform these functions. Many techniques such as carrier recovery , clock recovery , bit slip , frame synchronization , rake receiver , pulse compression , Received Signal Strength Indication , error detection and correction , etc., are only performed by demodulators, although any specific demodulator may perform only some or none of these techniques. Many things can act as

646-432: The fact that the human eye sees much more detail in contrast than in color. In addition, only blue and red are transmitted, with green being determined by subtracting the other two from the luminance and taking the remainder . (See: YIQ , YCbCr , YPbPr ) Various broadcast television systems use different subcarrier frequencies, in addition to differences in encoding . For the audio part, MTS uses subcarriers on

680-424: The higher frequencies of the FM multiplex. The extra RDS subcarriers are placed in the upper empty part of the multiplex spectrum and carry the extra data payload. xRDS has no fixed frequencies for the additional 57 kHz carriers. Until 2012, MSN Direct used subcarriers to transmit traffic, gas prices, movie times, weather and other information to GPS navigation devices, wristwatches , and other devices. Many of

714-407: The integrated subcarrier signal structure found in the transmitted baseband signal, while S-Video places the chrominance and luminance signals on separate wires to eliminate subcarrier crosstalk and enhance the signal bandwidth and strength (picture sharpness and brightness). Before satellite , Muzak and similar services were transmitted to department stores on FM subcarriers. The fidelity of

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748-475: The left channel and "subtracts" the right channel from it — essentially by hooking up the right-channel wires backward (reversing polarity ) and then joining left and reversed-right. The result is modulated with suppressed carrier AM , more correctly called sum and difference modulation or SDM, at 38  kHz in the FM signal, which is joined at 2% modulation with the mono left+right audio (which ranges 50 Hz ~ 15 kHz). A 19 kHz pilot tone

782-428: The message were lost due to buildings, tunnels or other obstructions of the FM signal. Error correction was 1/2 rate interleaved trellis with time diversity, soft-decision decode. The DirectBand data rate was in excess of 12 kbit/s after ECC. DirectBand was a push network – new content was delivered every two minutes. Users pre-selected the virtual channels that they were interested in. There were

816-449: The missing carrier wave from the 38 kHz signal. For AM broadcasting , different analog ( AM stereo ) and digital ( HD Radio ) methods are used to produce stereophonic audio. Modulated subcarriers of the type used in FM broadcasting are impractical for AM broadcast due to the relatively narrow signal bandwidth allocated for a given AM signal. On standard AM broadcast radios, the entire 9 kHz to 10 kHz allocated bandwidth of

850-486: The modulating audio signal, so it can drive an earphone or an audio amplifier. Fessendon invented the first AM demodulator in 1904 called the electrolytic detector , consisting of a short needle dipping into a cup of dilute acid. The same year John Ambrose Fleming invented the Fleming valve or thermionic diode which could also rectify an AM signal. There are several ways of demodulation depending on how parameters of

884-447: The provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadcast. There is no physical difference between a carrier and a subcarrier; the "sub" implies that it has been derived from a carrier, which has been amplitude modulated by a steady signal and has a constant frequency relation to it. Stereo broadcasting is made possible by using a subcarrier on FM radio stations , which takes

918-457: The receiver merely had to detect the presence or absence of the radio signal, and produce a click sound. The device that did this was called a detector . The first detectors were coherers , simple devices that acted as a switch. The term detector stuck, was used for other types of demodulators and continues to be used to the present day for a demodulator in a radio receiver. The first type of modulation used to transmit sound over radio waves

952-431: The service, it is not yet known whether the DirectBand technology will be sold to another company, such as one of the hardware licensees of MSN Direct (e.g. Garmin ) – or whether the technology will be put in the public domain as an open source technology. Subcarrier A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include

986-413: The studio), or any other use a TV station might see fit. (See also NICAM , A2 Stereo .) In RF-transmitted composite video , subcarriers remain in the baseband signal after main carrier demodulation to be separated in the receiver. The mono audio component of the transmitted signal is in a separate carrier and not integral to the video component. In wired video connections, composite video retains

1020-513: The subcarrier audio was limited compared to the primary FM radio audio channel. The United States Federal Communications Commission (FCC) also allowed betting parlors in New York state to get horse racing results from the state gaming commission via the same technology. Many non-commercial educational FM stations in the US (especially public radio stations affiliated with NPR ) broadcast

1054-577: The subcarriers were from stations owned by Clear Channel . The technology was known as DirectBand . FMeXtra on FM uses dozens of small COFDM subcarriers to transmit digital radio in a fully in-band on-channel manner. Removing other analog subcarriers (such as stereo) increases either the audio quality or channels available, the latter making it possible to send non-audio metadata along with it, such as album covers, song lyrics, artist info, concert data, and more. Many stations use subcarriers for internal purposes, such as getting telemetry back from

DirectBand - Misplaced Pages Continue

1088-560: The traffic data/local info market, particularly to auto GPS sets for Garmin and Avis. This competes directly with older RDS-based services, which operate at a substantially lower data rate. DirectBand is a product of the Smart Personal Objects Technology (SPOT) team at Microsoft. System hardware was designed for Microsoft by SCA Data Systems of Santa Monica, California. MSN Direct is the consumer brand that Microsoft uses for devices that receive content from

1122-435: The video that can also carry three audio channels, including one for stereo (same left-minus-right method as for FM), another for second audio programs (such as descriptive video service for the vision-impaired, and bilingual programs), and yet a third hidden one for the studio to communicate with reporters or technicians in the field (or for a technician or broadcast engineer at a remote transmitter site to talk back to

1156-410: Was amplitude modulation (AM), invented by Reginald Fessenden around 1900. An AM radio signal can be demodulated by rectifying it to remove one side of the carrier, and then filtering to remove the radio-frequency component, leaving only the modulating audio component. This is equivalent to peak detection with a suitably long time constant. The amplitude of the recovered audio frequency varies with

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