Abstract:
A system for sending uplink control signals to antennas and receiving downlink signals therefrom, where the uplink signals may be used to control antenna position and operate antenna switches and the like, and the downlink signals may indicate antenna position, the uplink signals being in the form of digital signals having two voltage levels within the range of a DC supply superimposed on the RF signals on the antenna feeder, and the downlink signals being digital signals in the form of changes in the DC current on the feeder, generated by a load having two resistance values.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a system for sending uplink control signals to antennas and receiving downlink signals therefrom. More particularly, the invention relates to a system where the uplink signals may be used to control antenna position and operate antenna switches and the like, and the downlink signals may indicate antenna position.  
         [0003]     2. Discussion of the Background  
         [0004]     It is relatively common, for example in amateur radio, to mount several antennas on a single mast or tower. Each of these antennas has to be connected via a length of high frequency feed line, such as a coaxial cable. Loss in these cables is proportional to length as well as to frequency. This can be mitigated by selecting low loss types of cables, but at significant cost. Directional antennas are often used to provide significant gain, but must then be rotatable to cover all directions. A remote antenna switch may be used to select the antenna in use, thereby consolidating the various coaxial cables, a single rotator may he use to rotate all the directional antennas in unison. However, typically, the antenna switch and the rotator each require separate power cables and control cables of their own. It is not uncommon for a rotator cable to have seven or eight wires. The height of the tower may be from, say 30 to 120 feet, and may be located at some distance from the radio equipment. The cost and complexity of cabling may therefore be very significant, even if a remote antenna switch is employed.  
         [0005]     It is known to supply DC power for accessories on coaxial. cables, for example to operate a masthead preamplifier. This eliminates the need to have separate power wiring as well as a coaxial cable for the antenna. Separation of the direct current and radio frequency components can be easily obtained using a suitable blocking capacitor. Rotators and antenna switches could be powered in the same way, but normally separate control cables would also be required.  
         [0006]     Van Amesfoort discloses a signaling scheme in U.S. Pat No. 6,075,970 in which a supply voltage of either 13 or 17 volts DC is sent over the feed line to select vertical or horizontal polarization, such as by selecting separate Low-Noise Convertors (LNCs) connected to vertical and horizontal feeds of a satellite TV dish. In this scheme the presence or absence of a separate 22 kHz AC signal is used to select one of two bands, such as X-band and L-band for satellite TV, and also bursts of the 22 kHz signal are used to send digital commands to the dish, but no telemetry is provided from the dish to the receiver. The only signal sent from the dish to the receiver is the RF output from one or the other LNC.  
         [0007]     The signaling scheme of Van Amesfoort is relatively complex, as it uses both DC signals and an audio tone. It also does not provide for any indication of the status of the remotely mounted antenna system, which includes only a single fixed antenna dish. A need exists, not only in radio installations, but also in other remote installations, for example with remote controlled TV cameras, for a simple two-way control system that can be combined with a remote power supply that can be superimposed on a radio frequency feed line such as a coaxial cable.  
       SUMMARY  
       [0008]     A system for sending uplink control signals to antennas and receiving downlink signals therefrom, where the uplink signals may be used to control antenna position and operate antenna switches and the like, and the downlink signals may indicate antenna position, the uplink signals being in the form of digital signals having two voltage levels within the range of a DC supply superimposed on the RF signals on the antenna feeder, and the downlink signals being digital signals in the form of changes in the DC current on the feeder, preferably generated by a load having two resistance values, as further discussed and as shown in the drawings 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a view of a system according to a preferred embodiment of the invention.  
         [0010]      FIG. 2  is a view of an uplink waveform according to a preferred embodiment of the invention.  
         [0011]      FIG. 3  is a partial block diagram of a remote unit according to a preferred embodiment of the invention, showing demodulation of the control signals.  
         [0012]      FIG. 4  is a partial block diagram of a remote unit according to a preferred embodiment of the invention, showing modulation of the load current.  
         [0013]      FIG. 5 . is a partial block diagram of a control unit according to a preferred embodiment of the invention, showing modulation of the DC supply voltage.  
         [0014]      FIG. 6 . is a partial block diagram of a control unit according to a preferred embodiment of the invention, showing demodulation of the downlink telemetry.  
         [0015]      FIG. 7 . is a block diagram showing a remote antenna switch.  
         [0016]      FIG. 8  is a view of an downlink waveform according to a preferred embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 1  is a view of a system according to a preferred embodiment of the invention. A transmitter  110  is connected via a short feed line  115  to a controller  120 , which is in turn connected via feed line  125  to remote unit  130 . Control inputs  150  are applied to control unit  120 . A further short feed line connects remote unit  130  to an antenna  140  and provides control signals at output  160 . Uplink signals from the controller  120  are recovered by the remote unit  130 , and may for example be used to control rotation of antenna  140  and/or to control an antenna switch to select between a plurality of antennas. For satellite working, i.e. for OSCAR satellites (Orbiting Satellites Carrying Amateur Radio), separate rotators may be simultaneously controlled for azimuth and elevation.  
         [0018]     Transmitter  110  may be a mere transmitter, or preferably a transceiver combining transmit and receive functions, or a receiver may be substituted therefor without departing from the scope of the invention. In addition, control unit  120  may optionally be integrated into the transmitter or transceiver  110 . More generally, the transmitter  110  and antenna  140  could be replaced with other types of electronic equipment. For example the antenna could be replaced with a TV camera and the transmitter with a TV monitor. The feed lines would typically be coaxial cable for radio frequency use, but other types of transmission line could conceivably be used.  
         [0019]     The uplink waveform is shown at  250  in  FIG. 2 . The upper and lower limits of the waveform are shown as 12 and 14 volts. It should be understood that these levels are exemplary only, but would be appropriate for equipment designed to run from a nominal 12 volt power supply, as is the case for most amateur radio equipment and much other communications equipment. Batteries that have a nominal voltage of 12 volts actually have a discharged voltage of around 12 volts, and normally charge up to around  14  volts, and therefore regulated ‘12 volt’ DC power supplies for communications use are typically in fact designed to output 13.8 volts. Consequently, most ‘12 volt’ communications equipment is designed for a working voltage range of at least 12 to 14 volts. This means that a digital signal where the two logic levels are 12 and 14 volts can be used both to power such equipment and to convey information, in this case control signals. It will be apparent to those skilled in the art that, for example, different logic levels would be necessary in a 24 volt system.  
         [0020]     To send downlink signals in the system of the present invention, the power supply current is optionally modulated. This can be achieved by switching a DC load, such as a resistor. This produces only a relative change in the DC current, which is of course also affected by any normal load current fluctuations for other reasons (e.g. starting and stopping an antenna rotator, etc). The uplink waveform  850  is shown in  FIG. 8 . When the DC load is applied the current has the lower value ‘L’ and when the DC load is not applied the current has the higher value ‘H’.  
         [0021]      FIG. 3  shows part of a remote unit  130  according to a preferred embodiment of the invention. Feed line  125  carries both an RF signal and DC from transmitter  110  and control unit  120 , which are fed into an RF/DC splitter  310 . From there the RF is fed via feed line  135  to antenna  140 . The DC voltage  315  from splitter  310  is filtered by filter  320  to provide a DC supply voltage  325 , which can then be used to power antenna rotators, a remote antenna switch, preamplifiers and/or any other accessories remotely located at the antenna  140 , or indeed at any other location connected to a control unit  120  by a high frequency feed line. The DC output  315  of the splitter  310  is also supplied to a voltage regulator  350  and via a voltage divider  360  to a voltage comparator  330 . The regulated voltage output  355  from the regulator  350  may be typically 6 volts, but it will be appreciated that other voltages nay be used. The voltage divider  360  reduces the voltage  315  into an appropriate range so that it can be demodulated by the comparator  330 , which is supplied from the regulator  350 . This arrangement enables the comparator  330  to run from a stabilized voltage  355 . The output voltage  335  from the voltage comparator  330  is then fed into a microprocessor  340 , which in turn takes the binary signal  335  and generates control outputs  345  in accordance with a stored program. The control outputs  345  may be used to control antenna rotators, remote antenna switches, preamplifiers, or any other devices. Suitable driver circuitry may of course be used to increase the amplitude of the various control outputs  345  to drive the controlled devices, as is well known in the art.  
         [0022]      FIG. 4  is a further partial diagram of the same remote unit  130  according to this preferred embodiment of the invention, showing modulation of the load current to carry telemetry from the antenna  140  to control unit  120 . Telemetry signals  445  may be derived from such parameters as antenna rotator position and/or remote antenna switch selection, and are fed into microprocessor  340 . In response to a stored program, microprocessor  340  sends a serial binary signal to switch  420 , which connects or disconnects a load  450 . The switch  420  is placed between the RF/DC splitter  310  and the filter  320 . Switching the load  450  modulates the DC current.  
         [0023]      FIG. 5 . is a partial block diagram of a control unit  120  according to a preferred embodiment of the invention, showing modulation of the DC supply voltage to carry control signals. RF from the transceiver  110  on feed line  115  passes through DC blocking capacitor  550  to RF/DC combiner  510  and thence via feed line  125  to the remote unit  130 . Control signals  545  are input to microprocessor  540 , which produces a serial binary output  535  in accordance with a stored program that in turn controls DC switch  520 . A source of DC power  515 , such as that obtained from a nominally 12 volt regulated power supply, is also applied to the DC switch  520 . The DC switch  520  modulates the DC voltage at  525  between, say approximately 12 and 14 volts in response to the binary signal  535 , and RF/DC combiner  510  combines the modulated DC voltage  525  with the RF on feed line  115  to produce a signal on feed line  125  that includes both RF and modulated DC power.  
         [0024]      FIG. 6 . is a partial block diagram of a control unit  120  according to a preferred embodiment of the invention, showing demodulation of the downwind telemetry. This shows a current detector  630  placed in between RF/DC combiner  510  and DC switch  520 . This detects changes in the DC current recovered from the RF/DC combiner  510  and outputs a serial binary signal  635  to microprocessor  540 , which, in response to a stored program, outputs separate telemetry outputs  645 , corresponding to telemetry inputs  445  in  FIG. 4 .  
         [0025]      FIG. 7 . is a block diagram showing a remote antenna switch  740 . A transmitter  110  is connected via a short feed line  115  to a controller  120 , which is in turn connected via feed line  125  to remote antenna switch  740 . Control inputs  150  are applied to control unit  120  to control antenna switch  740  to select between a plurality of antennas connected to terminals  735 .  
         [0026]     As will readily be appreciated by those skilled in the art, numerous modifications and variations of the above embodiments of the present invention are possible without departing from the scope of the invention.