GB2460012A

GB2460012A - Radio transceiver

Info

Publication number: GB2460012A
Application number: GB0803610A
Authority: GB
Inventors: Phil Longhurst
Original assignee: SRT MARINE TECHNOLOGY Ltd
Current assignee: SRT MARINE TECHNOLOGY Ltd
Priority date: 2008-02-27
Filing date: 2008-02-27
Publication date: 2009-11-18
Anticipated expiration: 2028-02-27
Also published as: GB2460012B; GB0803610D0

Abstract

Antenna splitter circuitry (20), comprising: a first terminal (22), for connection to first radio transceiver circuitry (12); a second terminal (24), for connection to second radio transceiver circuitry (14); a third terminal (26), for connection to an antenna (18); detecting circuitry (40,42), for detecting input signals at the first and second terminals (22,24); and switching circuitry (30,32), for connecting the first terminal (22) to the third terminal (26) when a first input signal is detected on the first terminal (22), for the transmission of said first input signal, and for connecting the second terminal (24) to the third terminal (26) when a second input signal is detected on the second terminal (24) but not on the first terminal (22), for the transmission of said second input signal. The invention allows multiple transceivers to share an antenna, for example VHF radios, AIS Class B transponders and FM radio receivers in marine vessels.

Description

RADIO TRANSCEIVER

This invention relates to a radio transceiver, and in particular to an antenna splitter, intended to allow multiple radio transmitter-receivers to share an antenna.

Many marine vessels need to use multiple radio transmitter/receivers, for example such as marine VHF radios, AIS (Automatic Identification System) Class B transponders, and FM radio receivers. Since these devices operate in similar frequency bands, they can use identical antennas. Therefore, in order to reduce costs, and the required installation effort, it is advantageous for them to share a single antenna.

However, in order for such an arrangement to operate successfully, it is necessary to ensure that the intended signals are correctly passed to and from the antenna.

According to a first aspect of the present invention, there is provided antenna splitter circuitry, comprising: a first terminal, for connection to first radio transceiver circuitry; a second terminal, for connection to second radio transceiver circuitry; a third terminal, for connection to an antenna; detecting circuitry, for detecting input signals at the first and second terminals; and switching circuitry, for connecting the first terminal to the third terminal when a first input signal is detected on the first terminal, for the transmission of said first input signal, and for connecting the second terminal to the third terminal when a second input signal is detected on the second terminal but not on the first terminal, for the transmission of said second input signal.

This has the advantage that transmission signals can be detected, and, when both connected transmission devices are attempting to transmit, a higher priority signal can be transmitted.

Preferably the detecting circuitry is configured to detect a low level first input signal when the input signal at the first terminal exceeds a first threshold value, and to detect a high level first input signal when the input signal at the first terminal exceeds a second threshold value higher than the first threshold value; the detecting circuitry is configured to detect a low level second input signal when the input signal at the second terminal exceeds a first threshold value, and to detect a high tevel second input signal when the input signal at the second terminal exceeds a second threshold value higher than the first threshold value; and the switching circuitry is configured to connect the first terminal to the third terminal when a low level first input signal is detected, and is configured to connect the second terminal to the third terminal when a low level second input signal is detected but a high level first input signal is not detected.

This has the advantage that, when one of the devices starts transmitting, the switching circuitry can quickly connect the intended input terminal to the output terminal, reducing the possibility that signals will be lost.

For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 shows radio transmission and reception circuitry, including an antenna splitter in accordance with the invention.

Figure 1 shows radio transmission and reception circuitry 10, of a type that may for example be used on marine vessels. As shown in Figure 1, the radio transmission and reception circuitry 10 includes a VHF radio 12, an AIS (Automatic Identification System) Class B transponder 14, and an FM radio receiver 16. All three of these devices share a single antenna 18.

In order to allow the sharing of the antenna 18, there is provided antenna splitter circuitry 20. The antenna splitter circuitry 20 has a first terminal 22, to which the VHF radio 12 is intended to be connected; a second terminal 24, to which the AIS Class B transponder 14 is intended to be connected; a third terminal 26, to which the antenna 18 is intended to be connected; and a fourth terminal 28, to which the FM radio receiver 16 is intended to be connected.

The first terminal 22 is connected to a first three-way RF switch 30, and the second terminal 24 is connected to a second three-way RE switch 32.

A filter diplexer 34 is connected to the third terminal 26 and the fourth terminal 28. A Wilkinson splitter 36 is connected to receive signals from the filter diplexer 34, and pass signals to the first and second RF switches 30, 32.

The antenna splitter 20 also includes detection, logic and control circuitry 38.

A small fraction of an input signal received on the first terminal 22 is tapped off through a directional coupler 40, in order to detect the presence of a transmission signal.

Where the VHF radio apparatus 12 is connected to the first terminal 22 as intended, this detects the presence of a signal being transmitted from the VHF radio. Similarly, a small fraction of an input signal received on the first terminal 24 is tapped off through a directional coupler 42, in order to detect the presence of a transmission signal. Where the AIS Class B radio apparatus 14 is connected to the second terminal 24 as intended, this detects the presence of a signal being transmitted from the AIS Class B radio.

The VHF detection signal is first applied to an amplifier 46, and the amplified signal is passed to a first detector 48 in the form of a first diode, which produces an output signal when the amplified VHF detection signal exceeds the first threshold value.

The VHF detection signal is also applied to a second detector 44 in the form of a second diode, which produces an output signal when the VHF detection signal exceeds a second threshold value.

Thus, the presence of the amplifier 46 means that the first detector 48 can be triggered by a VHF detection signal that is not large enough to trigger the second detector 44.

In addition, the Class B detection signal is applied to an amplifier 52, and the amplified signal is passed to a third detector 54 in the form of a third diode, which produces an output signal when the amplified Class B detection signal exceeds the first threshold value.

The Class B detection signal is applied to a fourth detector 50 in the form of a fourth diode, which produces an output signal when the Class B detection signal exceeds the second threshold value.

Thus, the presence of the amplifier 52 means that the third detector 54 can be triggered by a Class B detection signal that is not large enough to trigger the fourth detector 50.

The output signals from the first detector 48 and the third detector 54 are passed to the inverting input and the non-inverting input respectively of a first comparator 56.

The output signals from the first detector 48 and the third detector 54 are also passed to the non-inverting input and the inverting input respectively of a second comparator 58.

The output signals from the first comparator 56 and the fourth detector 50 are applied to the inputs of a first logical OR gate 60, while the output signals from the second comparator 58 and the second detector 44 are applied to the inputs of a second logical ORgate62.

The output signals from the first logical OR gate 60 and the second logical OR gate 62 are passed to combinational logic circuitry 64, which applies control signals to the first and second three-way RF switches 30, 32.

The operation of the antenna splitter circuitry 20 will now be described in more detail.

When a signal is received by the antenna 18, it is passed to the filter diplexer 34. In the illustrated embodiment, the antenna splitter 20 is suitable for use in a situation where the FM receiver 16 receives signals in a frequency band that is at a lower frequency than the frequency bands in which the VHF radio 12 and the Class B device 14 operate. Therefore, the filter diplexer 34 is adapted to pass the signals in the relevant FM frequency band to the fourth terminal 28, and hence to any connected FM receiver 16, while passing the remaining signals to the Wilkinson splitter 36.

As is conventional, the Wilkinson splitter 36 effectively divides the power of the received signals equally, passing one half of the received signal through the RF switch to the first terminal 22, and hence to a VHF radio 12 connected thereto, and passing the other half of the received signal through the RF switch 32 to the second terminal 24, and hence to a Class B device 14 connected thereto. Thus, a received signal that is intended for one of these devices will be received by that device with an amplitude that allows it to be acted upon as intended.

As described in more detail below, the antenna splitter circuitry 20 controls the operation of the transmit paths of the VHF radio and the Class B device 14, such that the higher priority signal can be transmitted via the antenna 18.

As mentioned above, small fractions of the input signals transmitted from the respective transmitting devices and received on the first and second terminals 22, 24 are tapped off, these fractions being small enough that the transmitted signals are not affected. In the illustrated configuration, when a signal is being transmitted from the VHF radio a signal appears at point A in the circuit and, when a signal is being transmitted from the AIS Class B radio a signal appears at point B in the circuit.

A VHF radio or an AIS Class B radio will typically transmit with a minimum power of 1W. The combinations of the directional coupler 40 and the second detector 44, and of the directional coupler 42 and the fourth detector 50, are such that they can detect signals on the respective inputs of, say, 0.5W or more. Thus, these detectors can detect signals during a transmission.

In addition, the signals at points A and B are amplified in amplifiers 46, 52, so that, even when these signals are relatively small, they are still large enough to trigger the relevant one of the detectors 48, 54. This means that the detectors are sensitive enough to react quickly to the presence of a transmitted signal when the transmitter is first switched on, so that transmitted information is not lost or corrupted. It will be noted that a VHF radio transmits at fu'l power whenever it is active, and that, even when there is an "audio silence" in the transmission and hence zero modulation of the carrier signal, the carrier signal is still detectable.

The time taken for one of the input signals to reach a level (say, 0.5W) that can be detected by the relevant one of the detectors 44, 50 will typically be less than lOps.

The detectors 48, 54 can therefore detect the input signals during the period before the input signals reach this level.

Based on the detected signals, the comparators 56, 58 then act so that the larger of the two signals detected by the detectors 48, 54 generates a positive signal on the output of the corresponding comparator 56, 58. That is, when the signal at point A is larger than the signal at point B, then there is a positive signal at point C on the output of the comparator 58, while when the signal at point B is larger than the signal at point A, then there is a positive signal at point D on the output of the comparator 56.

The output signals of the comparators 56, 58 are then combined in respective OR gates 60, 62 with the output signals of the detectors 50, 44.

Thus, the OR gate 60 produces a positive output signal when the signal at point B is larger than the signal at point A (by virtue of the first input to the OR gate 60), and whenever the signal at point B is large enough to trigger the fourth detector 50.

Similarly, the OR gate 62 produces a positive output signal when the signal at point A is larger than the signal at point B (by virtue of the first input to the OR gate 62), and whenever the signal at point A is large enough to trigger the second detector 44.

Any unwanted signal entering the antenna from an external source will be split equally by the Wilkinson splitter and presented equally to the detectors 48, 54. This will result in a zero difference between the signals on the inputs of the comparators 56, 58, and hence no change in the output of these comparators. This provides common mode rejection of the unwanted signals, and prevents the unwanted signals from falsely detecting the unwanted signal.

Thus, the operation of the detection and logic circuitry can be summarized in the

following table:-

Signal at point A Signal at point B output of OR gate output of OR gate VHF radio Class B device 60 62 0 0 0 0 0 1 1 0 1 0 0 1 1 1 1 1 To be more specific, the outputs of the OR gates 60, 62 respectively are 0,0 when the VHF radio 12 and the Class B device are both not in transmit mode, i.e. when neither signal is large enough to trigger the relevant detector 48, 54 even after amplification, or when neither signal is large enough to trigger the relevant detector 44, 50 and the two signals are of equal amplitudes.

The outputs of the OR gates 60, 62 respectively are 1,0 when the VHF radio 12 is not transmitting and the Class B device is transmitting, i.e. when the signal at point B is large enough to trigger the relevant high-level detector 50 and the signal at point A is not large enough to trigger the relevant high-level detector 44, or when the signal at point B is not large enough to trigger the relevant high-level detector 50 but is nevertheless large enough to trigger the relevant low-level detector 54 after amplification, and is larger than the signal at point A. Conversely, the outputs of the OR gates 60, 62 respectively are 0,1 when the VHF radio 12 is transmitting and the Class B device is not transmitting, i.e. when the signal at point A is large enough to trigger the relevant high-level detector 44 and the signal at point B is not large enough to trigger the relevant high-level detector 50, or when the signal at point A is not large enough to trigger the relevant high-level detector 44 but is nevertheless large enough to trigger the relevant low-level detector 48 after amplification, and is larger than the signal at point B. The outputs of the OR gates 60, 62 respectively are 1,1 when the VHF radio 12 and the Class B device are both transmitting, i.e. when both signals are large enough to trigger the relevant detectors 44, 50.

It should be noted that, when the VHF signal is high enough to be detected by the first detector 48, but not high enough to be detected by the second detector 44, and when the Class B signal is high enough to be detected by the third detector 54 and the fourth detector 50, then the outputs of the OR gates 60, 62 will be 1, 0 respectively.

However, since the Class B signal is typically only transmitted for 23ms in every 30s, and since the VHF signal typically reaches a level high enough to be detected by the second detector 44 within lOps, this situation is very unlikely to occur, and would be very short-lived, and hence is ignored in the analysis below.

Based on these OR gate output values, the combinational logic circuitry 64 can control the operation of the RF switches 30, 32 as required.

When the outputs of the OR gates 60, 62 respectively are 1,0, i.e. when the VHF radio 12 is not transmitting and the Class B device 14 is transmitting, the switches 30, 32 are controlled so that the transmitted signal from the Class B device 14 is passed through the switch 32 and through the filter diplexer 34 to the antenna 18, while the transmit path from the VHF radio 12 is connected through the switch 30 and terminated through an RF load 66.

When the outputs of the OR gates 60,62 respectively are 0,1, i.e. when the VHF radio 12 is on and the Class B device 14 is off, the switches 30, 32 are controlled so that the transmit path from the Class B device 14 is connected through the switch 32 and terminated through an RE load 68, while the transmitted signal from the VHF radio 12 is passed through the switch 30 and through the filter diplexer 34 to the antenna 18.

When the outputs of the OR gates 60, 62 respectively are 1,1, i.e. when the VHF radio 12 and the Class B device 14 are both on, priority has to be given to the VHF radio transmissions, as these may be safety critical. Therefore, in this situation, the switches 30, 32 are controlled so that the transmit path from the Class B device 14 is connected through the switch 32 and terminated through an RF load 68, while the transmitted signal from the VHF radio 12 is passed through the switch 30 and through the filter diplexer 34 to the antenna 18.

In an emergency situation, in which power to the antenna splitter circuitry 20 is lost, the switches 30, 32 go into a default mode, in which the transmit path from the Class B device 14 is connected through the switch 32 and terminated through an RF load 68, while the potentially safety critical transmitted signal from the VHF radio 12 is passed through the switch 30 and through the filter diplexer 34 to the antenna 18.

There is thus disclosed antenna splitter circuitry that allows two radio frequency transmitters to be connected to an antenna, and allows the signal from the one of these devices that is actually transmitting to be passed to the antenna, while allowing the signal from the higher priority device to be passed to the antenna when both devices are attempting to transmit.

Claims

CLAIMS1. Antenna splitter circuitry, comprising: a first terminal, for connection to first radio transceiver circuitry; a second terminal, for connection to second radio transceiver circuitry; a third terminal, for connection to an antenna; detecting circuitry, for detecting input signals at the first and second terminals; and switching circuitry, for connecting the first terminal to the third terminal when a first input signal is detected on the first terminal, for the transmission of said first input signal, and for connecting the second terminal to the third terminal when a second input signal is detected on the second terminal but not on the first terminal, for the transmission of said second input signal.
2. Antenna splitter circuitry as claimed in claim 1, wherein the detecting circuitry is configured to detect a low level first input signal when the input signal at the first terminal exceeds a first threshold value, and to detect a high level first input signal when the input signal at the first terminal exceeds a second threshold value higher than the first threshold value.
3. Antenna splitter circuitry as claimed in claim 1 or 2, wherein the detecting circuitry is configured to detect a low level second input signal when the input signal at the second terminal exceeds a first threshold value, and to detect a high level second input signal when the input signal at the second terminal exceeds a second threshold value higher than the first threshold value.
4. Antenna splitter circuitry as claimed in claim 1, wherein: the detecting circuitry is configured to detect a low level first input signal when the input signal at the first terminal exceeds a first threshold value, and to detect a high level first input signal when the input signal at the first terminal exceeds a second threshold value higher than the first threshold value; the detecting circuitry is configured to detect a low level second input signal when the input signal at the second terminal exceeds a first threshold value, and to detect a high level second input signal when the input signal at the second terminal exceeds a second threshold value higher than the first threshold value; and the switching circuitry is configured to connect the first terminal to the third terminal when a low level first input signal is detected, and is configured to connect the second terminal to the third terminal when a low level second input signal is detected but a high level first input signal is not detected.
5. Antenna splitter circuitry as claimed in claim 4, wherein the switching circuitry is further configured to determine the higher level signal of the first and second input signals, and to connect either the first terminal or the second terminal respectively to the third terminal when no high level first input signal or second input signal is detected.
6. Antenna splitter circuitry as claimed in any preceding claim, further comprising a splitter, connected to the third terminal, for splitting an input signal received thereat, and directing it to the first and second input terminals.
7. Antenna splitter circuitry as claimed in any preceding claim, further comprising a filter diplexer, connected to the third terminal, for receiving an input signal, and for directing signals within a predetermined frequency band to a fourth terminal.
8. Antenna splitter circuitry as claimed in claim 7, wherein the predetermined frequency band is an FM radio reception frequency band.
9. Antenna splitter circuitry as claimed in claim 7 or 8, when dependent on claim 6, wherein the filter diplexer is adapted to direct signals received at the third terminal, outside the predetermined frequency band, to said splitter.
10. Antenna splitter circuitry as claimed in any preceding claim, wherein the detecting circuitry is configured to detect a signal from a transmitting VHF radio transmitter at the first terminal.
11. Antenna splitter circuitry as claimed in any preceding claim, wherein the detecting circuitry is configured to detect a signal from a transmitting AIS Class B radio transmitter at the second terminal.
12. A radio transceiver system, comprising: antenna splitter circuitry as claimed in any preceding claim; a VHF radio transmitter, connected to the first terminal of the antenna splitter circuitry; an AIS Class B radio transmitter, connected to the second terminal of the antenna splitter circuitry; and an antenna, connected to the third terminal of the antenna splitter circuitry.