WO2005094154A2

WO2005094154A2 - Method and device for detecting an external antenna

Info

Publication number: WO2005094154A2
Application number: PCT/DK2005/000191
Authority: WO
Inventors: Poul Erik Schou-Pedersen
Original assignee: Kamstrup A/S
Priority date: 2004-03-31
Filing date: 2005-03-22
Publication date: 2005-10-13
Also published as: WO2005094154A3

Abstract

The invention relates to a method of external antenna detection and an antenna detector for detecting if an external RF antenna is connected to a transmitter via an external antenna connector. A first low frequency electrical signal is applied to a first conductor of the antenna via the connector, sensing a second low frequency electrical signal on a second conductor of the antenna via the connector, and detecting if the external antenna is connected to the transmitter by comparing the first and second low frequency electrical signals. Preferably, the first low frequency electrical signal is a DC voltage. Preferably, an external antenna is detected to be connected to the transmitter if a magnitude of the second low frequency electrical signal exceeds a predetermined value. In addition, the invention relates to a consumption meter, such as a gas, heat, liquid, such as water, or electricity meter, with an antenna detector according to the described principle.

Description

METHOD AND DEVICE FOR DETECTING AN EXTERNAL ANTENNA

Field of the invention

The present invention relates to the field of radio frequency (RF) antenna devices. More specifically the invention relates to a method and a device for detection of the presence of an external antenna connected to an external antenna connector. Furthermore, the invention relates to a consumption meter with a built-in antenna for wireless transmission of a measured consumed quantity, wherein the consumption meter has an antenna switch adapted to switch between the internal antenna and an optional external antenna upon connection of such external antenna. Background of the invention

A large amount of wireless equipment, especially mobile equipment, has a built-in internal antenna. However, in some environments such internal antennas may result in a poor radio transmission. Therefore, such wireless equipment often has a connector for connecting a more efficient external antenna via a cable, such as a coaxial cable. In addition to the external antenna being more efficient it may be positioned in a more advantageous position relative to an associated receiver antenna, so as to obtain a radio transmission path with less influence from rigid obstacles.

For the above-mentioned wireless equipment with optional external antennas a simple manual switch for electrical switching between the internal and the optional external antenna. However, such manual switch may cause malfunction if not operated correctly by the user. There will be no use of the external antenna if the external antenna is properly connected but the internal antenna has been selected by the user. Very poor transmission will result if the manual switch is set to "external antenna" and no such external antenna is connected. In case of infrequently used transmission equipment such as a transmitter in a consumption meter adapted for wireless reading, erroneous operation of a manual switch such as described above may be difficult and expensive to reveal.

Summary of the invention

It may be seen as an object to provide a simple and low cost detector for detecting if an external antenna is connected to a transmitter via an external antenna connector, thus enabling an automatic selection of such external antenna as an active antenna.

The above mentioned object is complied with by providing in a first aspect a method for detecting if an associated external antenna having a first and a second conductor is connected to a transmitter, the method comprising the steps of: a) applying a first low frequency electrical signal to the first conductor, b) sensing a second low frequency electrical signal on the second conductor, and c) comparing the first and second low frequency electrical signals.

Preferably, the step c) comprises a step of comparing a first magnitude of the first low frequency electrical signal to a second magnitude of the second low frequency electrical signal. The first and second magnitudes may comprise a step of comparing a ratio between the first and second magnitudes with a predetermined value.

The first low frequency electrical signal has a frequency spectral content within the frequency range 0-10000 Hz, preferably within the frequency range 0-100 Hz. The first low frequency electrical signal may be a pure tone. Preferably, the first low frequency electrical signal is a DC signal.

In a second aspect, the invention provides an antenna detector adapted to detect if an external antenna having a first and a second conductor is connected to a transmitter, the detector comprising

- detection signal means for providing a first low frequency electrical signal to the first conductor, - a sensor for sensing the first low frequency electrical signal at the first conductor and a second low frequency electrical signal at the second conductor, and

- detecting means for comparing the first and second low frequency electrical signals and for generating a detector signal upon detection of the external antenna using a result of the comparison of the first and second low frequency electrical signals.

Preferably, the sensor may be adapted to sense a first magnitude of the first low frequency electrical signal and a second magnitude of the second low frequency electrical signal.

The detecting means may be adapted to compare the first and second magnitudes. The detecting means may be adapted to compare a ratio between the first and second magnitudes with a predetermined value.

The detection signal means may be adapted to generate a first low frequency electrical signal exhibiting a frequency spectral content within the range 0-10000 Hz, preferably within the range 0-100 Hz. The detection signal means may be adapted to generate a first low frequency electrical signal being a pure tone. Preferably, the detection signal means is adapted to generate a first low frequency electrical signal being a DC signal.

In an embodiment, the antenna detector further comprises antenna selector means for establishing RF contact between the transmitter and

1) the external antenna in response to the control signal, and 2) an internal antenna otherwise.

The antenna selector means preferably comprises an electronic switch.

In a third aspect, the invention provides a consumption meter for measuring a quantity value corresponding to a consumed quantity and transmitting said quantity wirelessly to an associated remote receiver, the consumption meter comprising:

- measuring means for measuring the quantity value,

- an internal antenna,

- transmitter means for generating a RF signal according to the measured quantity value,

- an external antenna connector for connecting an associated external antenna, and

- an antenna detector according to any of claims 8-17.

In an embodiment of the consumption meter, the internal antenna is a dual band antenna.

The associated external antenna may be a dual band antenna.

The transmitter means for generating the RF signal may be adapted to generate frequency diversity signals so as to provide frequency diversity communication using a dual band antenna.

The consumption meter may be adapted to measure an amount of liquid, such as water, heat, electricity, gas, or a combination of two or more of these consumption quantities.

Brief description of drawings

In the following the invention is described in details with reference to the accompanying figures of which

Fig. 1 shows a diagram representing a first method of detecting an external antenna,

Fig. 2 shows a diagram representing a second method of detecting an external antenna,

Fig. 3 shows a diagram representing a third method of detecting an external antenna, and

Fig. 4 shows a consumption meter with an automatic antenna switch that allows automatic switching between an internal antenna and an external antenna. While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

Detailed description of the invention

In the following it is assumed that in an associated external antenna exhibits a low DC electrical resistance between its two connection conductors, such as substantially a DC short circuit between its connection conductors. In order to reduce the risk for lighting hazards most antennas are provided with a short circuit between its electrically conductive radiating elements without influencing the RF properties of the antenna.

Fig. 1 shows a diagram illustrating a first method of detecting the presence of an external antenna 4 connected to a connector 1 having a first conductor 2 and a second conductor 3. The connector may be a socket for receiving a plug connected to a coaxial cable. According to the first method a DC voltage source 5 applies a voltage VI to the first conductor 2. A DC voltage sensor 6 senses a voltage V2 at the second conductor 3. In case the external antenna 4 is connected to the connector 1, i.e. the external antenna is in electrical contact with both the first conductor 2 and the second conductor 3, then the external antenna will substantially short-circuit the first conductor 2 and the second conductor 3. Consequently, the voltage sensor 6 will sense a DC voltage V2 being substantially equal to the voltage VI. If the external antenna 4 is not connected to the connector 1, then the first conductor 2 and the second conductor 3 are not in electrical contact, and consequently the voltage sensor 6 will sense a DC voltage V2 of zero, or at least V2 will be very low.

Therefore, V2 can be compared to a predetermined voltage level set up as a criterion for determining if an external antenna 4 is connected to the connector 1 or not. For example the criterion for V2 for detecting the external antenna 4 could be a percentage of VI, such as 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 95% of VI. If V2 is above the predetermined level then an external antenna 4 is detected, and if V2 is below the predetermined level, then no external antenna 4 is detected.

Fig. 2 shows a diagram illustrating a second method of detecting the presence of an external antenna 14 connected to a connector 11 having a first conductor 12 and a second conductor 13. A DC voltage source 15 applies a voltage V to the first conductor 12. A current sensor 16 connected between the voltage source 15 and the second conductor 13 senses a current I in the circuit between the first conductor 12 and the second conductor 13. In case the external antenna 14 is not connected to the connector 11, then the circuit is open, and the sensed current I will be zero, or at least very small. In case the external antenna is connected to the connector, the circuit will be short-circuited and the sensed current I will be large, depending on the total resistance in the circuit. Preferably the voltage source 15 is a high impedance type. If a low impedance type voltage source 15 is applied, then a resistor (not shown) may be inserted in the circuit so as to reduce the current when an external antenna 14 is connected.

Therefore, the sensed current I may be compared to a predetermined current level set up as a criterion for determining if an external antenna 14 is connected to the connector 11 or not. If I is above the predetermined current level, then an external antenna 14 is detected, and if I is below the predetermined current level, then no external antenna 14 is detected.

Fig. 3 shows a diagram illustrating a third method of detecting the presence of an external antenna 24 connected to a connector 21 having a first conductor 22 and a second conductor 23. A resistance sensor 25 is connected between the first conductor 22 and the second conductor 23 so as to sense a resistance R between the conductors 22, 23. The sensed resistance R will depend on the presence of the external antenna 24. If the external antenna 24 is connected to the connector 21, then the sensed resistance R will be very small, such as close to zero, since the conductors 22, 23 will be short-circuited. In case there is no external antenna 24 connected to the connector 21, then the sensed resistance R will be very large. Typically, sensing a resistance between the conductors 22, 23 will include applying a DC voltage to the conductors 22, 23, additionally sense a resulting current, and finally apply Ohm's first law for calculating the resistance.

The sensed resistance R may be compared to a predetermined resistance level set up as a criterion for determining if an external antenna 24 is connected to the connector 21 or not. If R is below the predetermined resistance level, then an external antenna 24 is detected, and if R is above the predetermined resistance level, then no external antenna 24 is detected.

In principle the first, second and third methods described, and other methods as well, may be applied using an AC voltage instead of a DC voltage for detection of the external antenna. For example a sinusoidal voltage with a frequency of 1 Hz, 50 Hz, 100 Hz, 1 kHz or even higher, as long as the frequency is low enough so as not to interfere with the RF signals for which the external antenna is to be used. However, it may for simplicity reasons be preferred to use a DC voltage since filtering becomes simpler than by using an AC voltage for detection. Most often a DC voltage is used to power supply electronic means in equipment where an antenna detector is relevant. Hereby, the power supply DC voltage is used as signal generator for the detection signal thus eliminate the need for separate signal generator electronics which would otherwise be required in case of an AC voltage as detection signal.

The principles of detecting an external antenna connected to a transmitter via an external antenna connector according to the invention may advantageously be utilised for integration with an automatic antenna selector. The detector principles according to the invention enables a simple and low cost automatic antenna selector that is capable of routing a RF signal from a transmitter to an active antenna being either an internal antenna or an external antenna, if such external antenna is connected to the transmitter via an external antenna connector. In the following an embodiment of such an automatic antenna selector or automatic antenna switch is described integrated into a consumption meter adapted for wireless reading.

Fig. 4 illustrates an electrical diagram sketch of a consumption meter 30 adapted for wireless reading. The consumption meter 30 has a measuring module 31 for measuring a consumption quantity, for example a quantity of electricity, gas, liquid, such as water, or heat supplied by a supplier via a supplier network to a consumer. A radio transmitting module 32 is adapted to generate a RF signal corresponding to a consumption quantity value determined by the measuring module 31. The RF signal from the radio transmitting module 32 is provided to an input of an automatic switch 33 adapted to route the RF signal to an internal antenna 35 or to an external antenna connector 36 positioned on an exterior surface of the consumption meter 30.

The automatic switch 33 operates according to a detection of the presence of an external antenna 37 connected to the external antenna connector 36. Preferably, the automatic switch 33 has detecting means 34 operating according to one of the described first, second or third methods. The detecting means 34 of the automatic switch 33 then controls a two- position switch of the automatic switch 33 according to the detection of an external antenna 37 connected to the connector 35. If the detecting means 34 has detected an external antenna 37 connected to the connector 35 the two-position switch is set to route the RF signal to the connector 35 and thus to the external antenna 37. If the detecting means 34 has detected that there is no external antenna 37 connected to the connector 35, then the two-position switch is set to route the RF signal to the internal antenna 34.

Preferably the controllable two-position switch of the automatic switch 33 is an electronic switch. However, if preferred it could be implemented by mechanical means such as with a relay etc.

A fourth method of detecting an external antenna connected to an external antenna connector, will now be illustrated by the device of Fig. 4 as an example. The automatic switch 33 has an electronic two-position switch that is by default set to route an RF signal from the transmitting module 32 to the internal antenna 35. The detecting means 34 is adapted to generate a signal that forces the two-position switch to route the RF signal from the transmitting module 32 to the external antenna connector 36 if a control input of the detecting means 34 is connected to a DC voltage source, for example a general DC supply voltage of the consumption meter 30. This DC voltage source is connected to a first conductor of the external antenna connector 36, and the control input of the detecting means 34 is then connected to a second conductor of the external antenna connector 36.

In case the external antenna 37 is connected to the external connector 36, then the first and second conductors of the external antenna connector 36 are short-circuited and as a result the DC voltage source is connected to the control input of the detecting means 34 thus forcing the two-position switch to select the external antenna. The detecting means 34 may be designed to force the switch to select the external antenna if a detected DC voltage at the control input exceeds a predetermined voltage level, such predetermined voltage level being determined from a percentage of the DC voltage applied to the first conductor of the external antenna connector 36. In case the external antenna 37 is not connected to the external antenna connector 36, then the switch will remain in its default position thus selecting the internal antenna 35.

The internal antenna 35 as well as the associated external antenna 37 may be dual band antennas, and the transmitter module 32 may be adapted to transmit RF signals using either a first or a second frequency band for transmission. For example the consumption meter 30 may be designed to transmit a read value at a first band of 434 MHz, i.e. the ISM band, and a second band of 910 MHz, i.e. the GSM band. In case of either one or both of the antennas 35, 37 being dual band antennas, the transmitter module 32 may be designed to utilise the two bands for frequency diversity transmission.

A consumption meter 30 designed for wireless reading, such as the one illustrated and described in relation to Fig. 4, may be installed indoors in a consumer's dwelling. Due to different mounting positions and locations of buildings and other obstacles transmission conditions will be different among the consumers. However, one single type of consumption meter 30 may be installed at all consumers coupled to a supplier's supply net. Most preferably the internal antenna 35 is to be used to transmit in the ISM band. If no reliable contact can be established in this way, the internal antenna 35 may be tested in the GSM band. If this does not result in a reliable contact, then an external antenna must 37 be installed, such as mounted on an exterior surface of the consumer's house, and connected to the external antenna connector 36. Compared to a solution with a manual internal/external antenna switch an automatic switch 33 has the advantage that an installation person only needs to mount the external antenna 37 and connect it to the external antenna connector 36 thus leaving no opportunity for erroneous switch settings that may cost another service visit at the consumer.

The external antenna detector principles have been described in relation to connection between RF transmitters and antennas. It is to be understood, however, that the principles apply for connection between RF receivers and antennas as well. The same antenna may be used for both transmitting and receiving RF signals, such as if it is connected to a combined transmitter/receiver module.

Claims

1. Method for detecting if an associated external antenna having a first and a second conductor is connected to a transmitter, the method comprising the steps of: a) applying a first low frequency electrical signal to the first conductor, b) sensing a second low frequency electrical signal on the second conductor, and c) comparing the first and second low frequency electrical signals.

2. Method according to claim 1, wherein step c) comprises a step of comparing a first magnitude of the first low frequency electrical signal to a second magnitude of the second low frequency electrical signal.

3. Method according to claim 2, wherein the comparison of the first and second magnitudes comprises a step of comparing a ratio between the first and second magnitudes with a predetermined value.

4. Method according to any of the preceding claims, wherein the first low frequency electrical signal has a frequency spectral content within the frequency range 0-10000 Hz.

5. Method according to claim 4, wherein the first low frequency electrical signal has a frequency spectral content within the frequency range 0-100 Hz.

6. Method according to any of the preceding claims, wherein the first low frequency electrical signal is a pure tone.

7. Method according to any of the preceding claim 1-5, wherein the first low frequency electrical signal is a DC signal.

8. Antenna detector adapted to detect if an external antenna having a first and a second conductor is connected to a transmitter, the detector comprising

- detection signal means for providing a first low frequency electrical signal to the first conductor,

- a sensor for sensing the first low frequency electrical signal at the first conductor and a second low frequency electrical signal at the second conductor, and - detecting means for comparing the first and second low frequency electrical signals and for generating a detector signal upon detection of the external antenna using a result of the comparison of the first and second low frequency electrical signals.

9. Antenna detector according to claim 8, wherein the sensor is adapted to sense a first magnitude of the first low frequency electrical signal and a second magnitude of the second low frequency electrical signal.

10. Antenna detector according to claim 9, wherein the detecting means is adapted to compare the first and second magnitudes.

11. Antenna detector according to claim 10, wherein the detecting means is adapted to compare a ratio between the first and second magnitudes with a predetermined value.

12. Antenna detector according to any of claims 8-11, wherein the detection signal means is adapted to generate a first low frequency electrical signal exhibiting a frequency spectral content within the range 0-10000 Hz.

13. Antenna detector according to claim 12, wherein the detection signal means is adapted to generate a first low frequency electrical signal exhibiting a frequency spectral content within the range 0-100 Hz.

14. Antenna detector according to any of the preceding claims, wherein the detection signal means is adapted to generate a first low frequency electrical signal being a pure tone.

15. Antenna detector according to any of claims 8-13, wherein the detection signal means is adapted to generate a first low frequency electrical signal being a DC signal.

16. Antenna detector according to any of claims 8-15, further comprising antenna selector means for establishing RF contact between the transmitter and 1) the external antenna in response to the control signal, and

2) an internal antenna otherwise.

17. Antenna detector according to claim 16, wherein the antenna selector means comprises an electronic switch.

18. A consumption meter for measuring a quantity value corresponding to a consumed quantity and transmitting said quantity wirelessly to an associated remote receiver, the consumption meter comprising:

- measuring means for measuring the quantity value,

- an internal antenna, - transmitter means for generating a RF signal according to the measured quantity value,

- an external antenna connector for connecting an associated external antenna, and 5 - an antenna detector according to any of claims 8-17.

19. A consumption meter according to claim 18, wherein the internal antenna is a dual band antenna.

10 20. A consumption meter according to claim 18 or 19, wherein the associated external antenna is a dual band antenna.

21. A consumption meter according to claim 19 or 20, wherein the transmitter means for 15 generating the RF signal is adapted to generate frequency diversity signals.

22. A consumption meter according to any of claims 18-21, wherein the consumption meter is adapted to measure an amount of water.

20 23. A consumption meter according to any of claims 18-21, wherein the consumption meter is adapted to measure an amount of heat.

24. A consumption meter according to any of claims 18-21, wherein the consumption meter is adapted to measure an amount of electricity.

25 25. A consumption meter according to any of claims 18-21, wherein the consumption meter is adapted to measure an amount of gas.