Abstract:
An improved in-building radio frequency communications system with automatic failover recovery comprising a primary external antenna and at least one ancillary external antenna, each antenna directed to a primary transmission tower and to at least one ancillary transmission tower, respectively, and a diversity site donor system capable of monitoring the strength and/or quality of the radio frequency signals received from the primary transmission tower and switching communications between the primary transmission tower and the ancillary transmission tower(s) based on the strength and/or quality of the radio frequency signals received from the primary transmission tower.

Description:
FIELD OF THE INVENTION 
   The invention relates to the field of in-building radio communication coverage enhancement. Specifically, the invention provides a solution to maintain radio communication coverage inside a facility when the primary radio transmission tower providing the radio communication signals to the in-building system fails or is taken out of operation for maintenance or service. The invention will detect that the signals from the primary transmission tower are not viable and automatically connect radio communication signals from an alternate transmission tower to the in-building system electronics and signal distribution system. 
   BACKGROUND OF THE INVENTION 
   Wireless communication devices, such as cell phones and two-way radios, are becoming ever more popular. Such devices typically receive and transmit radio frequency (RF)signals from and to remote RF signal transmission towers, such as cell towers. While RF signals are capable of penetrating solid objects, the strength and quality of those signals degrade as more barriers are present between the transmission tower and the wireless communication device. Signal degradation is especially acute within structures, such as office buildings or factories, which offer multiple barriers between the transmission tower and the wireless communication device. 
   In-building radio frequency communications systems have been developed to improve performance of wireless communication devices within structures. These systems typically use a strategically located and directed antenna, which typically is located on the exterior of the structure (roof or side wall), providing a communications link with a RF signal transmission tower. The directed antenna is focused at a specific RF signal transmission tower (primary RF signal donor site) in an effort to maximize desired signal levels from the donor site to the in-building system. In addition, the directed antenna will minimize the level of non-desired and interference producing signals that arrive at angles, relative to the direction that the external antenna is focused, outside the horizontal beamwidth of the external antenna. The desired effect of the directed antenna is to isolate the in-building system from all RF signals other than those used at the primary donor site. They also use one or more low profile antennas located within the interior of the structure, strategically placed to provide coverage in areas where the RF signal levels and/or quality are not adequate to support reliable transmissions. The internal antennas are linked together by an infrastructure comprised of coaxial fiber optic and/or network cables and power splitters. The infrastructure is typically connected with the external antenna through a bi-directional amplifier (BDA), a device that increases the strength of the signal passing through it, either as the signal is received from the transmission tower to be transmitted to the wireless communication device (the signal downlink) or as the signal is received from the wireless communication device to be transmitted to the transmission tower (the signal uplink). In such a system, the RF signals are 1) received from the transmission tower by the external antenna and connected to the BDA; 2) amplified by the BDA; 3) distributed via the system infra-structure to the internal antennas, whose quantity and location inside the facility are appropriate to meet system requirements; and 4) radiated at a sufficient level to support reliable radio communications. The net effect is to allow the signals to pass between the transmission tower and the external antenna and between the wireless communication device and the internal antennas with relatively few intervening barriers. This minimization of intervening barriers, together with the signal amplification provided by the BDA greatly improves in-building performance of wireless communication devices. 
   In-building radio frequency communications systems are well known in the prior art, and may be implemented in any number of ways. See, e.g., Point-To-Multipoint Digital Radio Frequency Transport, U.S. Pat. No. 6,704,545 (Wala), issued Mar. 9, 2004; Communication System Comprising An Active-Antenna Repeater, U.S. Pat. No. 5,832,365 (Chen, et al.), issued Nov. 3, 1998; Method Of Locating A Mobile Station In A Mobile Telephone, U.S. Pat. No. 5,634,193 (Ghisler), issued May 27, 1997. However, while these systems are designed to handle the communications within a building, they all depend on reliable signals from the radio frequency transmission tower to support in-building transmissions. Thus, in-building signal enhancement tends to be susceptible to failure if there is an interruption or degradation of service at the external radio frequency transmission tower. This may result from a mechanical failure, a planned maintenance shutdown, environmental factors such as a lightning strike, or other causes, most of which are beyond the control or even awareness of the end use of the wireless communications device. In-building radio frequency communications systems known in the prior art are unable to recover from such interruptions and thus fail to provide the level of quality and reliability desired by end users. 
   One class of in-building frequency communications system known in the art does exemplify some failure recovery properties. Where an omni-directional antenna is used as the external antenna for an in-building system, by design the omni-directional antenna sends and receives RF signals equally in the horizontal plane, compared to a directional antenna, which will focus RF energy from approximately 15° to 100° of the horizontal plane. When an omni-directional antenna is used as the external antenna for an in-building system, there may be some degree of radio frequency transmission site diversity due to the inherent ability of the omni-directional antenna to transmit/receive RF signals equally in the horizontal plane. Under this scenario, signals from more than one radio frequency transmission tower may be connected into the in-building system and if signals from one radio frequency transmission tower fail, signals from a different radio frequency tower may be available to provide a level of coverage inside the facility. However, this configuration does not allow for specific redirection for precise control over alternative RF signal sources. The present invention, by placing such control with the system designer, is an improvement over in-building systems that have been designed to provide radio frequency transmission tower diversity through the use of an omni-directional external antenna. 
   The present invention is directed to an in-building radio frequency communications system with the capability to automatically transfer RF signals to the in-building system from multiple radio frequency transmission towers. As such, it offers improved RF signal access reliability over known systems. 
   It is an object of this invention to provide a fault tolerant in-building radio frequency communications system which minimizes disruptions due to failure of the RF signals from the primary radio frequency transmission tower. 
   It is a further object of this invention to provide a donor site diversity system which continuously detects the strength and quality of RF signals from a primary radio frequency transmission tower in order to automatically switch an in-building radio frequency communications system to an ancillary radio frequency transmission tower whenever the strength and quality of RF signals from a primary radio frequency transmission tower fall below an acceptable threshold. Other objects of this invention will be apparent to those skilled in the art from the description and claims which follow. 
   SUMMARY 
   The present invention is directed to an in-building radio frequency communications system with fault tolerant capability when RF signals from the primary radio frequency transmission tower are compromised or fail. Specifically, the invention relates to an improved system which incorporates into an in-building radio frequency communications system a primary external antenna and at least one ancillary external antenna, with the primary external antenna oriented to receive and transmit RF signals from and to a primary transmission tower, and the ancillary external antenna oriented to receive and transmit RF signals from and to one (or more) ancillary transmission towers. 
   The present invention further integrates an RF signal detection and switching mechanism into the in-building radio frequency communications system, the said detection and switching mechanism having two functions: 1) the detection mechanism constantly monitors the strength and quality of the RF signals received from the primary transmission tower; and 2) whenever the strength and/or quality of those RF signals deteriorates below a certain threshold, the switching mechanism redirects communications for the in-building radio frequency communications system to the ancillary transmission tower. The redirection of communication signals is achieved by toggling a switch within the switching mechanism, resulting in the circuit between the in-building system and the primary external antenna being interrupted and the circuit between the in-building system and the ancillary external antenna being completed, thereby establishing communications with the ancillary transmission tower. When the switching mechanism detects sufficient signal quality and/or strength in the RF signals received from the primary transmission tower, the switch is toggled to complete the circuit between the in-building system and the primary external antenna and to interrupt the circuit between the in-building system and the ancillary external antenna, thereby re-establishing communications with the primary transmission tower. 
   The above-described improvements to in-building radio frequency communications systems increase the reliability of communications in the event of disruptions from the primary transmission tower. By automatically redirecting the RF signal to a different transmission tower having sufficient performance criteria, the invention minimizes communications interruptions to in-building users of the system, achieving high levels of overall fault tolerance in the system. 
   The invention also contemplates using any number of ancillary external antennas directed at a like number of ancillary transmission towers. The ancillary transmission towers are prioritized, and the RF signal strength/quality detection component of the invention is employed for each ancillary transmission tower, except for the ancillary transmission tower designated as lowest priority. Upon detecting a sufficient loss of signal strength or quality from the primary transmission tower, the switching mechanism toggles to each successive ancillary transmission tower in turn, by order of priority, based on the detected signal strength/quality, until one receiving a sufficient strength and quality signal is detected. The strength and quality of signals received from the various transmission towers may be continuously monitored, with the switching mechanism toggling to the highest priority transmission tower having sufficient signal strength and quality. This configuration works best in densely populated geographies having multiple transmission towers within range of the system. 
   Other features and advantages of the invention are described below. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing depicting the basic components of the present invention, including a donor site diversity system. 
       FIG. 2  is a schematic drawing depicting the basic components of the present invention, together with detail of the components comprising the donor site diversity system. 
       FIG. 2A  is a schematic drawing depicting the basic components of the present invention, together with detail of the components comprising the signal splitting means of the donor site diversity system. 
       FIG. 3  is a schematic drawing depicting the basic components of the present invention, together with detail of the components comprising the donor site diversity system when multiple ancillary antennas are used. 
       FIG. 4  is a flowchart showing the process for determining which RF signal transmission tower should be used when the in-building radio frequency communication system comprises a primary external antenna and a single ancillary external antenna. 
       FIG. 5  is a flowchart showing the process for determining which RF signal transmission tower should be used when the in-building radio frequency communication system comprises a primary external antenna and multiple ancillary external antennas. 
   

   DESCRIPTION OF THE INVENTION 
   The invention is an improvement on known in-building radio frequency communications systems designed to be installed and used within structures, such as office buildings, power generation plants, correctional facilities, etc. The basic in-building system is comprised of the following components: a primary external antenna  32 , an ancillary external antenna  34 , an internal antenna  30 , a donor site diversity system  10 , and a bi-directional amplifier  20 . These components are networked together to form the in-building radio frequency communications system. In one embodiment, the donor site diversity system  10  is connected with the primary external antenna  32  and with the ancillary external antenna  34  by coaxial cables and/or fiber optic cables, and the bidirectional amplifier  20  is connected with the donor site diversity system  10  and with the internal antenna  30  by coaxial cables and/or fiber optic cables. This configuration is shown in  FIG. 1 . 
   The primary external antenna  32  must be configured to receive and transmit RF signals  5 , which are used for communications with cell phones, two-way radios, and the like. The primary external antenna  32  typically should be located on the exterior of a structure where it can be directed to a primary RF signal transmission tower  42 , such that the primary external antenna  32  is capable of transmitting and receiving RF signals  5  to and from the primary RF signal transmission tower  42 . In the preferred embodiment, the primary external antenna  32  is located on the roof of the structure, or other location with an unobstructed path to the primary RF signal transmission tower  42 . The primary RF signal transmission tower  42  is selected as providing the strongest and/or highest quality RF signal  5  available to connect with the in-building radio frequency communications system. 
   The ancillary external antenna  34  must also be configured to receive and transmit RF signals  5 . The ancillary external antenna  34  typically should be located on the exterior of the structure where it can be directed to an ancillary RF signal transmission tower  44 , such that the ancillary external antenna  34  is capable of transmitting and receiving RF signals  5  to and from the ancillary RF signal transmission tower  44 . Because the ancillary external antenna  34  is directed to an ancillary RF signal transmission tower  44  generating RF signals  5  which when received are of a lower strength and/or quality than the RF signals  5  generated by the primary RF signal transmission tower  42 , the ancillary external antenna  34  may be required to be of higher gain and greater directivity; for example, the ancillary external antenna  34  may be a parabolic grid-type antenna, whereas the primary external antenna  32  may be of lower gain and directivity, such as a corner reflector or yagi type antenna. Other types of higher gain and greater directivity antennas may also be used. Use of a higher gain and greater directivity ancillary external antenna  34  increases the likelihood that the RF signals  5  received from the ancillary RF signal transmission tower  44  and passed on to the bi-directional amplifier  20  will be of comparable strength and quality as those received from the primary RF signal transmission tower  42 . In the preferred embodiment, the ancillary external antenna  34  is located on the roof of the structure. The ancillary RF signal transmission tower  44  is selected as providing the next strongest and/or highest quality RF signal  5  available to the in-building radio frequency communications system, after the primary RF signal transmission tower  42 . 
   The internal antenna  30  must be configured to receive and transmit RF signals  5 . The internal antenna  30  is typically a low-profile antenna with a power output significantly less than that of the primary  42  and secondary  44  radio transmission towers. The internal antenna(s)  30  typically is located within the interior of the structure where it is capable of transmitting and receiving RF signals  5  to and from wireless communication devices  50  located within the structure. In the preferred embodiment, multiple internal antennas  30  are located within the structure, with each internal antenna  30  configured to receive and transmit RF signals  5 . The multiple internal antennas  30  are distributed throughout the interior of the structure so as to provide the greatest practical coverage within the structure, such that each of the internal antennas  30  is capable of transmitting and receiving RF signals  5  to and from nearby wireless communication devices  50 . Each of the internal antennas  30  is connected with the bi-directional amplifier  20 , either directly or indirectly via a network of cables. In the preferred embodiment, the network connecting the internal antennas  30  is comprised of coaxial cables, although other infrastructure configurations exist, such as fiber optic and network (CAT5/6) cable type systems. 
   The bi-directional amplifier  20  may be any type of RF signal amplifier known in the art capable of increasing the strength of RF signals  5 . The bi-directional amplifier  20  must be capable of increasing the strength of RF signals  5  downlinked from RF signal transmission towers to be transmitted to personal communications devices, and capable of increasing the strength of RF signals  5  uplinked from wireless communication devices to be transmitted to RF signal transmission towers. The bi-directional amplifier  20  is connected with the donor site diversity system  10 , from which it receives the downlinked RF signals  5  and to which it sends uplinked RF signals  5 , and is connected with the internal antenna  30 , from which it receives the uplinked RF signals  5  and to which it sends downlinked RF signals  5 . In the preferred embodiment, the bi-directional amplifier  20  is located proximate to the donor site diversity system  10 . 
   The donor site diversity system  10  is connected with the primary external antenna  32  and with the ancillary external antenna  34 . The donor site diversity system  10  monitors the strength and quality of the RF signals  5  received by the primary external antenna  32  from the primary RF signal transmission tower  42 . The donor site diversity system  10  is further capable of switching the communication connection between the primary RF signal transmission tower  42  and the ancillary RF signal transmission tower  44 , based on the strength and quality of the RF signals  5  received from the primary RF signal transmission tower  42 . 
   In one embodiment, the donor site diversity system  10  comprises a primary circuit  12 , an ancillary circuit  14 , a RF signal switch  16 , and a RF signal detector/sensor  18 . This configuration is shown in  FIG. 2 . 
   The primary circuit  12  is configured to establish a communications connection between the primary external antenna  32  and the bi-directional amplifier  20  such that RF signals  5  may travel between the primary external antenna  32  and the bi-directional amplifier  20 . The ancillary circuit  14  is configured to establish a communications connection between the ancillary external antenna  34  and the bi-directional amplifier  20  such that RF signals  5  may travel between the ancillary external antenna  34  and the bi-directional amplifier  20 . The primary circuit  12  and the ancillary circuit  14  are mutually exclusive; that is, when the primary circuit  12  is active, the ancillary circuit  14  is inactive, and RF signals  5  are received by and sent from the in-building radio frequency communications system solely through the primary circuit  12 ; and when the ancillary circuit  14  is active, the primary circuit  12  is inactive, and RF signals  5  are received by and sent from the in-building radio frequency communications system solely through the ancillary circuit  14 . 
   The RF signal switch  16  is configured to activate and deactivate the primary circuit  12  and to activate and deactivate the ancillary circuit  14 . In the preferred embodiment, the RF signal switch  16  toggles an interlink  17  between the primary circuit  12  and the ancillary circuit  14 , such that the ancillary circuit  14  is interrupted when the interlink  17  is toggled to and completes the primary circuit  12 , and the primary circuit  12  is interrupted when the interlink  17  is toggled to and completes the ancillary circuit  14 . 
   The RF signal detector/sensor  18  is configured to monitor the strength and quality of the RF signals  5  received from the primary RF signal transmission tower  42 . In one embodiment, the RF signal detector/sensor  18  comprises a monitoring means and a logic processor appropriate to the target RF signals  5  enhancing the in-building environment. The monitoring means is configured to monitor the strength and quality of the RF signals  5  received from the primary RF signal transmission tower  42 . In the preferred embodiment, the monitoring means is configured to continuously monitor the strength and quality of the RF signals  5  received from the primary RF signal transmission tower  42 . The logic processor of the RF signal detector/sensor  18  is connected with the RF signal switch  16 , and is configured to determine the sufficiency of the strength and quality of the RF signals  5  received from the primary RF signal transmission tower  42 . The threshold criteria for determining the sufficiency of the strength and quality of the RF signals  5  may be preset, or altered by the user, or dynamically altered automatically depending on environmental criteria. The logic processor compares the sufficiency of the strength and quality of the RF signals  5  against the threshold criteria, and communicates a positive signal to the RF signal switch  16  if the sufficiency of the strength and quality of the RF signals  5  meets or exceeds the threshold criteria, and communicates a negative or ground signal to the RF signal switch  16  if the sufficiency of the strength and quality of the RF signals  5  fails to meet or exceed the threshold criteria. The RF signal switch  16  in turn toggles the interlink  17  to complete the primary circuit  12  when a positive signal is received, thereby interrupting the ancillary circuit  14 , and toggles the interlink  17  to complete the ancillary circuit  14  when a negative signal is received, thereby interrupting the primary circuit  12 . This process is shown in  FIG. 4 . 
   In one embodiment, the donor site diversity system  10  further comprises a signal splitting means for directing RF signals  5  to both the RF signal detector/sensor  18  and the RF signal switch  16 . In the preferred embodiment the signal splitting means comprises an unequal power signal splitter  60 , a two-way power divider  64 , and a variable attenuator  68 . The unequal power signal splitter  60  further has an input port  61 , a high power output port  62 , and a low power output port  63 . The two-way power divider  64  further has an input port  65 , a first equal power distribution output port  66 , and a second equal power distribution output port  67 . The unequal power signal splitter  60  is located in-line with the primary circuit  12 , whereby the unequal power signal splitter  60  is in connection with the primary external antenna  32  through the input port  61  of the unequal power signal splitter  60 , the unequal power signal splitter  60  is in connection with the RF signal switch  16  through the high power output port  62  of the unequal power signal splitter  60 , and the unequal power signal splitter  60  is in connection with the two-way power divider  64  through the low power output port  63  of the unequal power signal splitter  60  and into the input port  65  of the two-way power divider  64 . RF signals  5  from the primary external antenna  32  enter the unequal power signal splitter  60  through its input port  61  and are directed simultaneously to the RF signal switch  16  and the two-way power divider  64 . The two-way power divider  64  in turn is in connection with a test port through the first equal power distribution output port  66  of the two-way power divider  64  and with the variable attenuator  68  through the second equal power distribution output port  67  of the two-way power divider  64 . The variable attenuator  68  is in connection with the RF signal detector/sensor  18 . The variable attenuator  68  is used to adjust the threshold level of the RF signal detector/sensor  18 . RF signals received by the primary external antenna  32  are transmitted along the primary circuit  12  to the unequal power signal splitter  60 , whereby the RF signals  5  are then split between the RF signal switch  16  and the RF signal detector/sensor  18  (the latter by way of the two-way power divider  64  and variable actuator  68 ). In using the combination of the unequal power signal splitter  60  and the two-way power divider  64  to send RF signals  5  to the RF signal switch  16  and the RF signal detector/sensor  18 , the monitoring means of the donor site diversity system  10  can monitor the strength and/or quality of the RF signals  5  received from the primary RF signal transmission tower  42  on a continuous basis. The RF signal detector/sensor  18  then directs the RF signal switch  16  to toggle between the primary circuit  12  and the ancillary circuit  14  as appropriate. 
   In an alternate embodiment of the invention, the in-building radio frequency communications system comprises multiple ancillary external antennas  34 . This configuration is shown in  FIG. 3 . Each of the ancillary external antennas  34  is configured to receive and transmit RF signals  5 , and each of the ancillary external antennas  34  is located on the exterior of the structure, preferably on the roof, where it can be directed to a corresponding ancillary RF signal transmission tower  44 , one ancillary RF signal transmission tower  44  per ancillary external antenna  34 . Each ancillary external antenna  34  is capable of transmitting and receiving RF signals  5  to and from its corresponding ancillary RF signal transmission tower  44 . As in the preferred embodiment, the ancillary external antennas  34  may be required to be of higher gain and greater directivity than the primary external antenna  32 . For each of the ancillary external antennas  34 , there is a corresponding ancillary circuit  14 . Each such ancillary circuit  14  is configured to establish a connection between the corresponding ancillary external antenna  34  and the bi-directional amplifier  20 , with one ancillary circuit  14  per ancillary external antenna  34 , such that RF signals  5  may travel between each ancillary external antenna  34  and the bi-directional amplifier  20 . Each of the ancillary RF signal transmission towers  44  is prioritized based on the strength and/or quality of the RF signals  5  received by the in-building radio frequency communications system under optimal conditions, with all ancillary RF signal transmission towers  44  having a lower priority than the primary RF signal transmission tower  42 . 
   In this embodiment, the donor site diversity system  10  is connected with each of the multiple ancillary external antennas  34 , in addition to the primary external antenna  32 . As in the preferred embodiment, the RF signal detector/sensor  18  of the donor site diversity system  10  monitors the strength and quality of the RF signals  5  received by the primary external antenna  32  from the primary RF signal transmission tower  42 . However, the RF signal detector/sensor  18  also monitors the strength and quality of the RF signals  5  received by each of the ancillary external antennas  34  from their corresponding ancillary RF signal transmission tower  44 , except for the ancillary RF signal transmission tower  44  having the lowest priority, which is not monitored. The monitoring means may be configured to continuously monitor the strength and quality of the RF signals  5  received by each of the external antennas  32 , 34 . 
   The logic processor of the RF signal detector/sensor  18  is configured to determine the sufficiency of the strength and quality of the RF signals received from each of the monitored radio frequency signal transmission towers  42 , 44 , in conjunction with the priority established for each of the RF signal transmission towers  42 ,  44 . The logic processor compares the sufficiency of the strength and quality of the RF signals  5  received from each monitored radio frequency transmission tower  42 , 44  against the threshold criteria, in order of priority, and for each such tower  42 , 44  communicates a positive signal to the RF signal switch  16  if the sufficiency of the strength and quality of the RF signals  5  meets or exceeds the threshold criteria, and communicates a negative or ground signal to the RF signal switch  16  if the sufficiency of the strength and quality of the RF signals  5  fails to meet or exceed the threshold criteria. The RF signal switch  16  in turn toggles the interlink  17  to complete the circuit  12 , 14  corresponding to the positive signal, thereby interrupting all other circuits. Once a positive signal is communicated by the logic processor to the RF signal switch  16 , the process is reset and the logic processor repeats the process beginning with the primary RF signal transmission tower  42 . 
   The determination of which RF signal transmission tower  42 , 44  is to be used for the communication connection by the donor site diversity system  10  in this embodiment is illustrated in  FIG. 5 . The logic processor of the RF signal detector/sensor  18  begins the process with an analysis of the RF signals  5  received from the primary RF signal transmission tower  42 . When the strength and quality of the RF signals  5  received from the primary RF signal transmission tower  42  is sufficient, the donor site diversity system  10  switches the communications connection to the primary RF signal transmission tower  42 , along the primary circuit  12 , and all ancillary circuits  14  are disabled. The process then repeats. If, however, the strength and quality of the RF signals  5  received from the primary RF signal transmission tower  42  is insufficient, the donor site diversity system  10  determines whether the strength and quality of the RF signals  5  received from the ancillary RF signal transmission tower  44  having the highest priority is sufficient; if so, the donor site diversity system  10  switches the communications connection to that ancillary RF signal transmission tower  44 , along its corresponding ancillary circuit  14 , disabling the primary circuit  12  and all other ancillary circuits  14 , and the process then repeats. If the strength and quality of the RF signals  5  received from the ancillary RF signal transmission tower  44  having the highest priority is insufficient, the strength and quality of the RF signals  5  received from the ancillary RF signal transmission tower  44  having the next highest priority is analyzed by the donor site diversity system  10 , etc. If no monitored ancillary FR signal transmission tower  44  is transmitting RF signals  5  of sufficient strength and quality, the donor site diversity system  10  switches the communications connection to the ancillary RF signal transmission tower  44  having the lowest priority, along its corresponding ancillary circuit  14 , disabling the primary circuit  12  and all other ancillary circuits  14 . 
   This embodiment may also comprise multiple signal splitter means  60 A,  60 B. Each signal splitter means is configured as explained above. One signal splitter means  60 A is located in-line with the primary circuit  12  between the primary external antenna  32  and the RF signal switch  16 , and is in connection with the RF signal detector/sensor  18 . Each of the monitored ancillary circuits  14  also is assigned a signal splitter means  60 B, with one signal splitter means for each such ancillary circuit  14 . Each such signal splitter means is located in-line with its ancillary circuit  14  between the corresponding ancillary external antenna  34  and the RF signal switch  16 , and is in connection with the RF signal detector/sensor  18 . RF signals  5  received by the primary external antenna  12  and by each monitored ancillary external antenna  14  are transmitted through the corresponding signal splitter means to both the RF signal switch  16  and the RF signal detector/sensor  18 . In using the signal splitter means, the monitoring means of the donor site diversity system  10  can monitor the strength and/or quality of the RF signals  5  received from the RF signal transmission towers  42 , 44  on a continuous basis. 
   Modifications and variations can be made to the disclosed embodiments of the invention without departing from the subject or spirit of the invention as defined in the following claims.