Patent Publication Number: US-2005143047-A1

Title: Low noise and distortion adapter and system for providing audio output signals from the auxiliary SDARS radio to the in-vehicle AM/FM radio

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to the in-vehicle audio systems, and more particularly, to an adapter that allows an auxiliary novel SDARS (Satellite Digital Audio Radio Services) receiver to be connected to the in-vehicle high-fidelity sound systems through a factory-installed in-dash AM/FM radio.  
      2. Description of Related Art  
      Some SDARS receivers (Satellite Digital Audio Radio Services Receiver) are added on to an existing in-vehicle audio system as novel aftermarket (not OEM) satellite-delivered radio. Add-on components have to be communicated with in-dash AM/FM head unit radio through the various kinds of adapters. Brand name, called AM/FM head units, allow to connect any auxiliary source (cassette, MP3, CD, etc.) with RCA outputs to the AUX audio input. Just the auxiliary source must have a standard level of output voltage, or a volume control to adjust output level.  
      If SDARS radio is connected to car stereo via the AUX input, hard-wired system does not have any quality losses of audio signal, but a direct ground connection has a lot off problems. RCA cable and common power line are picking up some kind of in-vehicle electrical interference: either alternator “whine” or popping noise (ignition, sparkplugs), or the “hiss” (white) noise and so on. The best way to fix is using a complementary GLI (Ground Loop Isolator) device with optional standard chock inductor of 10 millihenry hooked in series with the power line to the each SDARS, AM/FM radio and head-end car audio devices. Howevr, audio performance still will be so sensitive to the in-vehicle wire routing and chassis (ground) connection quality.  
      Other way for in-vehicle audio system integration is a short-range wireless communication links. A lot of wireless frequency modulated (FM) systems were described in prior art to eliminate hard wiring and electrical conductors.  
      This conventional technique is disclosed in, for example, U.S. Pat. No. 5,970,390 and U.S. Pat. No. 6,493,546 B2. System has additional scanning receiver seeking an empty or unused frequency within a FM broadcasting band and having the lowest noise floor. Automatically detected empty frequency is set to the FM transmission. This kind of adapters needed a microcomputers control, are so bulky, expensive and can avoid only interference with commercial broadcast FM signals, but not to overcome FM transmission limitation.  
      The fundamentals of FM transmission haven&#39;t changed since the 1950s, and it&#39;s definitely old school technology. The sound quality will be limited by the inherent limitations of FM radio itself: FM tuner only has a frequency response up to 15 kHz, signal-to-noise ratio around 60 db, limited dynamic range, reduced stereo channel separation, etc. In the road area of high environmental noise, such as vehicle engine ignition VHF noise, commercial FM broadcasts station signals, precipitation static etc., will affect and disturb audio signal transmitted to the in-dash vehicle FM radio receiver.  
      In-vehicle FM wireless link performance can be improved by increasing radiated power. Howevr, FM transmitters put out no more RF power then complies with the regulations in Part  15  of the FCC rules for low-power, non-licensed transmitter. The field strength must be limited to 250 microvolts per meter at a distance of 3 meters from the antenna.  
       FIG. 1   a , lb is a major block diagram of the conventional car audio system having the auxiliary SDARS receiver.  FIGS. 1   a ,  1   b  show a vehicle  10  equipped with conventional in-dash AM/FM radio  70  with external (or on-glass) antenna  40 . A novel Satellite Digital Audio Radio Services(SDARS; Satellite Digital Audio Radio Services) utilizing a satellite transmitter  20  and an on-roof mount satellite antenna  50  connected through RF coaxial cable  51  with on-board SDARS receiver  60 .  
      Usually SDARS receiver  60  and satellite antenna  50  are auxiliary aftermarket installed. Add-on SDARS receiver  60  has standard (stereo analog, digital or both) audio signal output. SDARS radio can be connected into car stereo  80  via the AUX input of in-dash AM/FM radio  70  using hard-wired audio cable system  61  and  71 .  
      A system for providing a wireless connection through the adapter  90  in accordance with the present invention is depicted in  FIG. 2 . Block diagram of a proposed adapter is shown in  FIG. 3 .  
      As shown in  FIG. 2  adapter can be used in two modes: first-wireless mode ( FIG. 2   a ) dedicated for pure wireless connection between SDARS receiver output and in-dash AM/FM radio  70  through the stationary antenna  40  and in adapter embedded antenna  92 . Second mode-adapter  90  can be used as a wired transmitter/modulator. In this mode ( FIG. 2   b ) in-dash AM/FM radio antenna input connected to the adapter RF FM output  91  through RF cable  91 . Stationary car antenna  90  also connected to the adapter input  99 .  
     SUMMARY OF THE INVENTION  
      In view of the above problems associated with the prior art, it is an object of this invention to provide improved an adapter equipped in between the auxiliary SDARS receiver and in-dash vehicle AM/FM radio. This adapter combines together a wireless FM communication links and a hard-wired RF link.  
      In certain instances, it is preferable to eliminate hard wiring and electrical conductors between SDARS radio and in-dash AM/FM radio. For example in case of portable, “Plug-and-Play” SDARS radios in vehicle installation. Howevr, for the situations when there are high environmental RF noise or FM wireless link destroyed by the interference with commercial broadcast FM station signals link performance will be improved by instant switching from wireless link to the transmission through RF cable.  
      There are many situations in which the present invention is particularly advantageous. Proposed adapter combines advantage from both wireless and hard-wired link sides. Especially, transmission of FM modulated signal into the in-dash AM/FM radio tuner through the RF coaxial cable provides superior RF signal and stereo audio quality. The user selects one of these modes with respect to sound quality. The adapter schematics have to provide instant mode switching with minimum manipulation. The adapter has FM modulator, RF power amplifier and embedded loop antenna, and switches between embedded antenna and external RF cable output. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1   a ,  1   b  are a perspective view for the major blocks of conventional in-vehicle audio system with the auxiliary SDARS receiver;  
       FIGS. 2   a ,  2   b  illustrate the car installation for the system in accordance with an embodiment of the present invention;  
       FIG. 3  is a block diagram for the proposed two-modes adapter; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Referring now to drawings, various preferred embodiments of the present invention will be described.  
       FIGS. 2   a ,  2   b  illustrate the car installation for the system in accordance with an embodiment of the present invention.  FIGS. 2   a ,  2   b  show a vehicle  10  equipped with convention (OEM installation) in-dash AM/FM radio  70  with external (or on-glass) antenna  40 . A novel Satellite Digital Audio Radio Services (SDARS; Satellite Digital Audio Radio Services) utilizing a satellite transmitter  20  and an on-roof mount satellite antenna  50  connected through RF coaxial cable  51  with on-board SDARS receiver  60 . Usually SDARS receiver  60  and satellite antenna  50  are auxiliary aftermarket installed. Add-on SDARS receiver  60  has standard (stereo analog, digital or both) audio signal output.  
      The existing SDARS radio can be connected into car stereo  80  via the AUX input of in-dash AM/FM radio  70  using hard-wired audio cable system  61  and  71 . On the other side, this invention provides a system of wireless connection to AM/FM radio  70  through the adapter. A system for providing a wireless connection through the adapter  90  in accordance with the present invention is depicted in  FIGS. 2   a ,  2   b . A block diagram of a proposed adapter is shown in  FIG. 3 .  
      As shown in  FIG. 2 , the adapter can be used in two modes: first-wireless mode ( FIG. 2   a ) dedicated for pure wireless connection between SDARS receiver output and in-dash AM/FM radio  70  through the stationary antenna  40  and in adapter embedded antenna  92 .  
      Second mode—the adapter can be used as a wired transmitter/modulator. In this mode ( FIG. 2   b ), in-dash AM/FM radio antenna input connected to the adapter RF FM output  91  through RF cable. Stationary car antenna  40  is also connected to the adapter input  99 .  
      As shown in  FIG. 3 , in order to provide wireless mode ( FIG. 2   a ), user interface unit  95  allows to switch in-dash AM/FM radio antenna input between stationary car antenna  40  and modulator RF output  91 . Namely, the first RF switch  96  is connected to input of the RF low power amplifier  98 . When AM/FM radio antenna input connected to modulator RF output  91  AM/FM radio can receive RF signal only from auxiliary SDARS receiver  60  with high fidelity because wired connection through cable  91  and disconnect unwanted, interference signal from antenna  40 . In this switches position, as the signal transmitted from SDARS receiver output to RF modulator, the first RF switch  96  and RF low-power amplifier through the level controller and pre-emphasis circuits  93 , the adapter has been used as modulator only.  
      As shown in  FIG. 3 , in order that the adapter is used as wireless FM link, user interface unit  95  also allows connection in-dash AM/FM radio antenna input directly to the stationary car antenna  40 . That is, the second RF switch  97  is connected to input of the adapter and the first RF switch  96  is connected to RF power amplifier  98 . In this position signal from RF modulator will be amplified by RF power amplifier unit  98  and radiated from embedded antenna  92 . In this connection AM/FM radio can to receive RF signal from AM/FM station and from auxiliary SDARS receiver  60  too.  
      In accordance with an aspect of the present invention, the interface adapter  90  can be easily reconfigured and implemented as a pure wireless FM transmitter or as a wired transmitter/modulator. This flexibility is advantageous and desirable to provide a method for aftermarket SDARS receiver  60  installation in variety of in-vehicle audio  80  and in-dash AM/FM radio  70  systems.  
      Furthermore, SDARS receivers as a digital radio have to provide a digital audio output signal, not only analog. Also a novel in-dash AM/FM radio can be a Digital Audio Broadcast (DAB) compatible systems, like in-band on-channel (IBOC) system as standard for USA, which use regular AM/FM radio frequencies to broadcast digital audio signals. In some embodiments of the present invention, it may be desirable to use adapter  90  with digital DAB compatible RF modulator unit  94 , not like analog stereo FM modulator. It should be noted that the adapter  90  structure and two mode adapter application variety did not depend analog or digital audio signal have to be transmitted form SDARS receivers to the car stereo through in-dash AM/FM radio.  
      Although the invention has been described and illustrated in the above description and drawings, it is understood that this description is by example only and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the this invention.  
      As described above, The adapter in accordance with this invention can provide high quality of link performance by instant switching from wireless link to wired link through RF cable in case that there is high environmental RF noise or even if FM wireless link is destroyed by interfering of FM commercial broadcast station signals.  
      Also, the adapter of this invention combines advantages both for wire and wireless links. Specially, this adapter provides excellent FM modulated signal and stereo audio performance to in-dash board AM/FM radio through RF coaxial cable