STATE OF THE ART A radio communication system usually operates in a frequency band specific to the system. As examples, the GSM system, the DCS1800 system, the PCS1900 system the AMPS system and the AMPS 1900 system may be mentioned. The downlink frequency bands for these radio communication systems are 935-960 MHz, 1805- 1880 MHz, 1930-1990 MI-Iz, 869-894 MHz, and 1930-1990 MHz, respectively.

A receiver that can be used for receiving radio signals or radio frequencies in one of the above mentioned radio communication systems, is the heterodyne receiver. A heterodyne receiver mixes the received radio signal down to a lower so called intermediate frequency before the signal is demodulated to the desired base band signal.

The reception takes place in the following way: the received radio signal first passes through a band pass filter, and is then amplified. Then a first intermediate frequency is generated by a mixer. The mixer mixes the radio signal with a local oscillator frequency, in the following called an LO frequency. The LO frequency is generated by an oscillator, for example, a voltage controlled oscillator, usually in combination with a synthesizer and a reference crystal. When mixing the LO frequency and the filtered and amplified signal, in a heterodyne receiver, the difference frequency between the two frequencies may be selected. A further mixing to a second intermediate frequency may be carried out before the final demodulation of the signal to the desired base band signal takes place.

It is becoming increasingly common that there is more than one radio communication system in service within a geographical area. The different radio communication systems then operate in completely separate frequency bands. It would then be desirable for a receiver in a mobile terminal to be able to receive signals from more than one frequency band.

It is also desirable for a mobile terminal moving from a geographical area covered by a first radio communication system to a geographical area covered by a second radio communication system utilizing a different frequency band from the first system to be able to receive signals in both frequency bands.

One way of designing a multiple band receiver that is able to receive radio signals from two different frequency bands is to use two separate single band receivers. One of the receivers receives radio signals in the lower frequency band of the two frequency bands and the other receiver receives radio signals in the upper frequency band. A switching device connects each respective receiver to an antenna depending on the frequency band received.

A disadvantage of the device described above is that such a multiple band receiver requires much space in a mobile telephone. Another disadvantage is that such a multiple band receiver becomes expensive to manufacture, as all components must be duplicated.

Another way of designing a multiple band receiver is described in the published European patent application EP 0678974. Certain parts of a heterodyne receiver are here reused for reception in two different frequency bands. The disclosed double band receiver utilizes two different oscillators that have one common synthesizer.

One of the oscillators is used to generate a first intermediate frequency for the upper frequency band and the other to generate the same first intermediate frequency for the lower frequency band. This implies that the two LO frequencies generated from the respective oscillator must be selected so that the frequency after the first mixer, that is, the first intermediate frequency, assumes the same value for both frequency bands. As the same first intermediate frequency is generated for the different frequency bands, the continued processing of the signals until a baseband signal has been obtained will be the same, independently of the received frequency band.

In the patent specification US 4972455 and in the published patent application EP 0541305 a multiple band receiver that can switch between receiving frequencies from two different frequency bands is disclosed. An oscillator is used to generate a first intermediate frequency. The first intermediate frequency differs for the different frequency bands, and thus different filters are used for the different intermediate frequencies in the intermediate frequency section of the receiver.

One disadvantage of these receivers is that it is necessary to change between different filters in the receiver depending on the frequency band being received.

In the patent specification US 5457734 a radio communication system is disclosed, the base stations of which are able to serve two different groups of mobile terminals operating in two separate frequency bands. A frequency converter converts downlink signals from the first subscriber group to the frequency band of the second subscriber group. Uplink signals from the second subscriber group are converted to the frequency band of the first subscriber group.

In the published patent application EP 0631400 a homodyne multiple band transceiver is disclosed, the receiving part of which can receive signals from hvo separate frequency bands, both from a satellite system and from a land based mobile system. A signal in the lower frequency band of the two bands is handled in the same way as in a common homodyne receiver, that is, it is converted directly to the base band. This is achieved by mixing the signal with an LO frequency generated by a voltage controlled oscillator. The LO frequency is of the same order of magnitude as the frequency of the signal in the lower frequency band. A signal in the upper frequency band of the two frequency bands is converted to substantially the lower frequency band through mixing with a converting frequency. The converting frequency is generated by dividing the LO frequency from the voltage controlled oscillator by a suitable integer. The signal is then demodulated in the same way as a signal in the lower frequency band. The invention will now be described in more detail by means of preferred embodiments and with reference to the accompanying drawing.

SUMMARY OF THE INVENTION The present invention attempts to solve the problem of how to design a multiple band receiver comprised in a mobile telephone in a simple and cost-effective way.

A further problem is how to design the multiple band receiver using as few components as possible, so that it becomes as compact as possible.

The problems are solved by designing a multiple band receiver in such a way that it only uses one oscillator to generate the same intermediate frequency for received radio signals in at least two different frequency bands. Radio signals from a first frequency band are converted substantially to a second frequency band, before the same oscillator is used by both frequency bands to generate a first intermediate frequency for frequencies in the second frequency band and/or for frequencies substantially in the second frequency band.

More specifically, the problems are solved by designing a multiple band receiver comprising at least one converting receiver part and a heterodyne receiver part. The heterodyne receiver part and the converting receiver part utilize LO frequencies generated by the same oscillator.

Radio signals in a first frequency band are received by an antenna connected to the converting receiver part. Through mixing with an LO frequency from the oscillator a received radio signal is converted to a second frequency band when the frequency bands are of the same size, or substantially to the frequency range of the second frequency band when the frequency bands have different bandwidths. The converting receiver part is connected to the heterodyne receiver part. The converted radio signal is mixed in the heterodyne receiver part, to a first intermediate frequency. In the mixing, the converted frequency is mixed with the same LO frequency that was used in the mixing in the converting receiver part.

When frequencies in the second frequency band are received by the antenna, the converting receiver part is bypassed, whereby the antenna is connected to the heterodyne receiver part. A received radio signal is mixed by the heterodyne receiver part with an LO frequency, generated by the oscillator, to the same first intermediate frequency generated for received radio signals in the second frequency band.

Switching devices are arranged for the connection of the antenna to one of the receiving parts and for the connection of the receiving parts to each other, depending on the frequency band of the received radio signal. The LO frequencies generated by the oscillator are equal to or approximately equal to the frequency spacing between the frequency bands.

The invention will now be described in more detail by means of preferred embodiments and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic block diagram of a heterodyne single band receiver known in the art.

Figure 2 is a schematic block diagram of a first embodiment of a multiple band receiver for receiving signals from two separate frequency bands according to the invention.

Figure 3 is a schematic block diagram of a second embodiment of a multiple band receiver for receiving signals in two different frequency bands according to the invention.

Figure 4 is a table of values of LO frequencies and intermediate frequencies for different combinations of radio communication systems.

Figure 5 is a schematic block diagram of a third embodiment of a multiple band receiver for receiving signals from three different frequency bands according to the invention.

Figure 6 is a schematic block diagram of a fourth embodiment of a multiple band receiver for receiving signals in three different frequency bands according to the invention.

PREFERRED EMBODIMENTS Figure 1 shows a schematic block diagram of a part of a prior art heterodyne single band receiver. A radio signal, or a radio frequency fRF, is received by an antenna ANT and then passes a bandpass filter BP adapted to the frequency band in question.

The filtered signal is amplified by an amplifier, for example a low noise amplifier LNA, to reduce the noise level. The amplified signal is then mixed with a local oscillator frequency or, with a shorter expression, an LO frequency fLO generated by an oscillator VCO, which may be, for example, a voltage controlled oscillator. The LO frequency is generated in a way common in the art by the oscillator VCO, by means of a reference frequency fR from a reference crystal REF and a synthesizer SYNT. The synthesizer and the oscillator are interconnected in a phase locked loop in a way common in the art, which is indicated in the figure by an arrow from the synthesizer to the oscillator and an arrow from the oscillator to the synthesizer. In the mixing, the frequency spacing fRF-fLO (in the case when fRF>fLO) between the LO frequency and the radio signal may be utilized, to obtain a first intermediate frequency fiFI- The first intermediate frequency fiFI can in turn be mixed down further to a second intermediate frequency before the final demodulation to a desired base band signal takes place. The reference frequency from the reference crystal may for example be multiplied by a factor and used by a further mixer generating the second intermediate frequency. This is, however, not shown in the figure.

A so called image frequency image may cause interference with the intermediate frequency after the mixer, as is known in the art. The image frequency is the frequency that equals the difference between the LO frequency and the intermediate frequency fIF, that is: image = fLo-IF (in the case when the LO frequency is higher than the intermediate frequency). If the image frequency is not within the bandwidth of the frequency band in question it has already been eliminated by the bandpass filter BP before the mixer MIX. If that is not the case the image frequency image must be removed before the mixer MIX. This may be done in a way common in the art, either by arranging a special image rejection filter before the mixer and/or by using as a mixer a so called image rejection mixer.

Below different embodiments of a multiple band receiver according to the invention are described. In all cases it is assumed that image rejection mixers or image rejection filters are used in the cases when the image frequency has to be eliminated.

Figure 2 shows a schematic block diagram of a first inventive embodiment of a multiple band receiver that can receive signals from two separate frequency bands.

The receiver comprises an antenna ANT, a heterodyne receiver part R2, a converting receiver part R1 and a device LO for generating LO frequencies. The converting receiver part R1 converts signals from an upper frequency band FBU of the two frequency bands to a lower frequency band FBL or substantially to the lower frequency band, as will be explained in more detail below.

The heterodyne receiver part R2 mixes down a signal from the lower frequency band FBL or from the area around the lower frequency band to a first intermediate frequency fIF 1. The device LO for generation of LO frequencies comprises an oscillator VCO, in the present case a voltage controlled oscillator, a synthesizer SYNT and a reference crystal REF, each operating in the same way as described above in connection with Figure 1.

In the following a first embodiment of the invention will be described, in which the two frequency bands are assumed to have the same frequency range. The antenna ANT receives a high frequency radio signal fRF in the upper frequency band FBU of the two frequency bands or from the lower frequency band FBL. The reception in the respective frequency band takes place at different times.

If it is assumed that a radio signal fRF received by the antenna ANT is in the upper frequency band FBU, the antenna ANT is connected through a first switch S1 to the converting receiver part R1 which is in turn connected through a second switch S2 to the heterodyne receiver part R2. If a received radio signal instead lies in the lower of the two frequency bands FBL the converting receiver part R1 is bypassed. The antenna ANT is then connected through the first switch S1 directly to the heterodyne receiver part R2. A radio signal in the upper frequency band will thus first pass the converting receiver part, in which it is converted to a signal in the lower frequency band. The signal processing then continues in the heterodyne receiver part in the same way as for a received radio signal in the lower frequency band. The switches may, as is well known in the art, comprise combinations of PIN diodes and so called strip lines.

It is also possible to design the multiple band receiver with only a first switch S1, in which case the converting receiver part is constantly connected to the heterodyne receiver part. In Figure 2 the switches arc shown in the position that they assume when the received radio signal lies in the lower frequency band. The case when the radio signal is in the upper frequency bands is indicated in the figure as a dashed line in the switches.

Assuming first that a radio signal fRF lying in the upper frequency band FBU is received by the antenna ANT, the radio signal will pass through the first switch S1 to the converting receiver part R1. This is illustrated in Figure 2 by an arrow from the first switch to the converting receiver part. The converting receiver part comprises a bandpass filter BP1 adapted to the upper frequency band FBU, an amplifier LNA1, in the present case a low noise amplifier, and a mixer MIX 1. In the mixer the filtered and amplified signal is mixed with an LO frequency fLO. The LO frequency is generated in a way known in the art by the device LO for generation of LO frequencies.

According to the invention, radio signals in the upper frequency band FBU are to be converted, through mixing with an LO frequency, to signals in the lower frequency band FBL. This implies that the LO frequency fLO must be equal to the frequency spacing between the two frequency bands.

The converted signal then passes the second switch S2 to the heterodyne receiver part R2. The heterodyne receiver part R2 comprises a bandpass filter BP2 adapted to the lower frequency band FBL, an amplifier, for example a low noise amplifier LNA2 and a mixer MIX2.

In the mixer MIX2 in the heterodyne receiver part R2 the converted signal is mixed with the same LO frequency used in the first mixer MIXI in the converting receiver part R1. In this way a first intermediate frequency fil l is obtained, which may be the frequency spacing between the converted signal and the LO frequency fLo.

If instead it is assumed that a radio signal fRF in the lower frequency band FBL is received by the antenna ANT, the converting receiver part Rl is bypassed. This means that the radio signal, via the first switch S 1 and via the second switch S2, passes directly to the heterodyne receiver part R1. This is illustrated in Figure 2 by an arrow from the first switch S 1 to the second switch S2. The radio signal then passes the previously mentioned bandpass filter BP2 and the low noise amplifier LNA2. The incoming signal is then mixed in the second mixer MIX2 with an LO frequency fLO generated by the device LO for generating LO frequencies. The LO frequency is selected so that the same first intermediate frequency fIFl is obtained as for radio signals received in the upper frequency band FBU.

The device LO for generating LO frequencies can generate LO frequencies within a frequency interval. The smaller this frequency interval is, the less disturbed the LO frequency will be. In order for a signal in the upper frequency band FBU to be converted to the lower frequency band FBL, the device LO for generating LO frequencies must generate LO frequencies the same size as the frequency spacing between the upper and the lower frequency band.

A signal in the lower frequency band FBL thus passes the same components that are found in a heterodyne single band receiver. A signal in the upper frequency band first passes the converting receiver part Rl in which the received signal is converted to a signal in the lower frequency band FBL. The converted signal then passes the same components in the heterodyne receiver part R2 as a signal in the lower frequency band. The LO frequencies are selected so that the same first intermediate frequency is generated for the signals in the upper and the lower frequency band.

Since different radio communication systems often utilize frequency bands of different bandwidth, the situation arises that one of the two received frequency bands is wider than the other. If the frequency bands have different bandwidths there is often not a fixed frequency spacing between the frequency bands. In the combinations of the previously mentioned radio communication systems, such as GSM/DCS1800, GSM/PCS1900, AMPS/AMPS 1900, the upper frequency band of the two frequency bands is wider than the lower frequency band.

In the following the multiple band receiver is described according to the embodiment shown in Figure 2, for the case when the upper frequency band is wider than the lower frequency band, as is the case for the above mentioned combinations of telecommunications systems.

A radio signal in the upper frequency band is received by the antenna ANT and is subjected to the same signal processing in the converting receiver part R1 as was described in the case of frequency bands of the same bandwidth. In the first mixer MIX1 in the converting receiver part R1, in the present case, the filtered and amplified signal is mixed with an LO frequency. As there is no fixed frequency spacing between the frequency bands, the generated LO frequency is approximately equal to or substantially equal to the frequency spacing between the two frequency bands. The frequency spacing between the two bands may for example be represented by the frequency spacing between the middle frequencies in the respective frequency band. The signals in the upper frequency band FBU are then converted to a frequency range that can be wider of somewhat displaced in relation to the lower frequency band FBL, depending on how big the bandwidth difference is between the frequency bands. The converted signals still end up substantially within the frequency area of the lower frequency and FBL.

The converted signal passes through the second switch S2 to the heterodyne receiver part R2. Since the converted signal may lie in a frequency area somewhat wider than the lower frequency band, or displaced relative to it, the passband of the bandpass filter BP2 in the heterodyne receiver part in the present case must be correspondingly wider than the lower frequency band. The passband in the bandpass filter BP2 in the heterodyne receiver part R2 must then be at least as wide as the lower frequency band FBL, but is in the present case wider.

Since the passband of the bandpass filter BP2 in the heterodyne receiver part R2 in the example above is somewhat wider than the lower frequency band, its edges should be very sharp. This may be a problem in certain applications, for example for GSM/PCS.

Figure 3 shows an alternative embodiment of a multiple band receiver that can receive signals from an upper and a lower frequency band, FBU, FBL, whereby the upper frequency band is assumed to be wider than the lower frequency band. The references used for the different components are the same as in Figure 2. The bandpass filter BP2 in the heterodyne receiver part R2, according to Figure 2, has been removed in the present example. Instead a bandpass filter BP2' has been arranged between the first and the second switch S 1 and S2. The passband of this bandpass filter is adapted to the bandwidth of the lower frequency band FBL and thus its passband does not have to be as wide as that of the second bandpass filter BP2 in Figure 2.

This solution implies high requirements on the bandpass filter BP1 and the mixer MIX1 in the converting receiver part R1, so that no undesired frequencies leak through the mixer MIX1 into the heterodyne receiver part R2. To prevent this, an additional bandpass filter, suppressing undesired frequencies, can be placed directly after the mixer MIX1 in the converting receiver part. This is, however, not shown in the figure.

The table in Figure 4 shows a compilation of some different combinations of radio communications systems, GSM/(DCS1800, GSM/PCS1900 and AMPS/AMPS 1900, which use two separate frequency bands. The upper frequency band is in all cases wider than the lower. The table shows the upper and the lower frequency bands FBU and FBL, examples of LO frequencies fLO for the respective frequency band FBU and FBL, and the converting frequency band FBL to which signals in the upper frequency band are converted. The intermediate frequencies fiFl obtained in this way are shown in the right column.

An example according to the table for the combination GSM/DCS 1800 will be explained in more detail. The upper frequency band FBU is in the present example the downlink band of the DCS1800 system and the bandwidth is 1805-1880 MHz.

The lower frequency band is the downlink band of the GSM system and the bandwidth is 935-960 MHz. Assuming that the lowest frequency of the upper frequency band FBU, 1805 MHz, is received and the desired intermediate frequency fiF, after the two mixings in the mixers MIX1 and MIX2 is 71 MHz, the LO frequency fLo will be 867 MHz. The received frequency will then fist be mixed with the LO frequency and converted to 938 MHz before it is mixed down with the same LO frequency to the first intermediate frequency.

Assuming that the lowest frequency in the lower frequency band FBL, 935 MHz, is received and the same intermediate frequency f of 71 MHz is to be obtained, the LO frequency must be 864 MHz.

Assuming that the highest frequency of the upper frequency band FBU, 1880 MHz, is received, the LO frequency fLO must be 904.5 MIIz, whereby the converting frequency is 975.5 MMz. The converting frequency then lies just outside of the lower frequency band, which ends at 960 MHz.

The frequency spacing between the lowest frequencies of the two frequency band is 870 MLIz and the frequency spacing between the highest frequencies of the frequency bands is 920 MHz. The intervals of the LO frequencies for the upper frequency band lie in the interval 867-904.5 MHz and the LO frequencies for the lower frequency band lie in the interval 864-889 MHz. Thus, the LO frequencies are approximately equal to the difference in frequency between the two frequency bands. Signals in the upper frequency band are converted to the converted frequency range FBL*, 938-975.5 MHz, and the lower frequency band FBL is 935-960 MHz, so that the converting frequency band does not lie entirely within the lower frequency band, but substantially in the frequency range of the lower frequency band.

Figure 5 shows an alternative embodiment of the invention in which the multiple band receiver is able to receive signals in a first, a second and a third frequency band FB l, FB2 and FB3. The third frequency band lies between the first and the second frequency bands and is therefore called the intermediate band. The first frequency band Fob 1 is in the present case the upper of the three bands and the second frequency band FB2 is the lower of the bands. It is assumed that the frequency spacing between the first frequency band and the intermediate band is as great or substantially as great as the frequency spacing between the intermediate band and the second frequency band.

The multiple band receiver in the present case comprises an antenna, a first converting receiver part Rl l, a second converting receiver part R1 and a heterodyne receiver part R2, and a device LO for generating LO frequencies, said device being used by all three receiver parts.

The second converting receiver part Rl and the heterodyne receiver part R2 correspond to the double band receiver described in connection with Figure 2. The references used for the components in the second converting part Rl and the heterodyne part R2 are the same as in Figure 2. That is, to the double band receiver an additional converting receiver part R1 1 has been added.

If the frequency bands have the same width, as described in connection with Figure 2, the first frequency band FB1 is converted in the first converting receiver part R11 to the intermediate band FB3. If that is not the case the first frequency band is converted to substantially the frequency range of the intermediate band. The continued signal processing in the second converting receiver part R1 and the heterodyne receiver part R2 thereafter are the same as described in connection with Figure 2.

The antenna ANT is connected via a first switch S1 to either the first converting receiver part RI 1 or the second converting receiver part R1 or the heterodyne receiver part R2. The first converting receiver part R1 1 is connected to the second converting receiver part via a second switch S2. The second converting receiver part is connected to the third converting receiver part R2 via a third switch S3. In Figure 5 the switches are shown in the position for reception of signals from the first frequency band. Each respective receiver part comprises a bandpass filter BP 11, BP1, BP2, a low noise amplifier LNA11, LNA1, LNA2 and a mixer MIX11, MIX1, MIX2. Each respective mixer is connected to the device LO for generating LO frequencies.

Assuming that a radio channel fRl. in the first frequency band FBl is received by the antenna ANT, the antenna is connected via the first switch S1 to the first converting receiver part Rl l. This is illustrated in Figure 5 by an arrow from the first switch S1 to the first converting receiver part Tri 1. The radio signal then passes a bandpass filter BP 1 for the first frequency range FBl, a low noise amplifier LNAl l and a mixer MIX11. In the mixer, the signal is mixed with an LO frequency fLO generated by the oscillator VCO. The LO frequency is equal to the frequency spacing between the first frequency band FBl and the intermediate band FB3, or the intermediate band FB3 and the second frequency band FB2, respectively, or if the frequency bands have different widths, approximately to these frequency spacings. In this way the signal in the first frequency band FBt is converted to, or substantially to, the intermediate band FB3.

The converted signal then passes via the second switch S2 to the second converting receiver part R1. This part comprises a bandpass filter BP1, a low noise amplifier LNA1 and a mixer MIX1. The mixer mixes the converted signal with the same LO frequency that was used in the first converting receiver part R11, whereby a second converted signal is obtained. The second converted signal will be within or substantially within the second frequency band FB2.

The second converted signal then passes, via the third switch S3, to the heterodyne receiver part R2. The second converted signal passes a bandpass filter BP2, a low noise amplifier LNA2 and another mixer MIX2. The second converted signal is mixed with the same LO frequency as before, whereby a first intermediate frequency fIFI iS generated.

Assuming, instead, that a radio signal fRF in the intermediate band FB3 is received, the first converting receiver part Ri 1 is bypassed. The antenna ANT is then connected directly to the second converting receiver part R1 via the first switch S I and the second switch S2. This is illustrated in Figure 5 by an arrow from the first switch S 1 to the second switch S2. The received signal is converted to the second frequency band FB2 or substantially to this frequency band. The signal is then converted by the heterodyne receiver part R1 to the same first intermediate frequency flFI as above.

Assuming instead that a radio signal fRF in the second frequency band FB2 is received by the multiple band receiver, both converting receiver parts Rl l, R1 are bypassed. The antenna ANT is then connected via the first switch S 1 and via the third switch S3 directly to the heterodyne receiver part R2. This is illustrated in Figure 5 by an arrow from the first switch S1 to the third switch S3. The signal is then converted to the same first intermediate frequency fIFI as above after first having been bandpass filtered and amplified.

In accordance with the embodiment shown in Figure 3, the bandpass filter BP2 in the heterodyne receiver part R2 may instead be located before the heterodyne receiver part, between the first and the third switch S 1, S3. In the same way the bandpass filter BP1 in the second converting receiver part R1 may be placed before the converting receiver part, between the first and the second switch S1, S2.

Figure 6 shows yet another embodiment of the invention in which three separate frequency bands are being received. In the present case the spacing between the first frequency band and the intermediate band is substantially less than the spacing between the intermediate band and the second frequency band. As an illustrative example, the combination of GSM, DCS1800/PCS1900 may be considered. The frequency spacing between the upper, or first, frequency band (PCSi900: 1930-1990 MHz) and the intermediate frequency band (DCS1800: 1805-1880 MHz) is approximately 120 MHz. The spacing between the intermediate band and the lower, or second, frequency band (GSM: 935-960 MHz) is approximately 900 MHz.

In this case as well, the receiver comprises an antenna ANT, a first R11 and a second R1 converting receiver part, a heterodyne receiver part R2 and a device LO for generating LO frequencies.

The same references as in Figure 5 have been used in Figure 6. The second converting receiver part R1 converts signals in a frequency range at least covering the intermediate band FB3, to substantially the second frequency band FB2. The heterodyne receiver part R2 generates a first intermediate frequency fiFl by mixing a signal within a frequency range at least covering the second frequency band FB2 with an LO frequency fLO generated in the same way as described above.

The first converting receiver part R11 converts a radio signal in the first frequency band FB l to substantially the frequency range of the intermediate band FB3. This is done in the same way as before, by mixing the signal with an LO frequency, said LO frequency being substantially equal to the frequency spacing between the first frequency band and the intermediate band. The LO frequency in the present case cannot assume the same value as the LO frequency used by the second converting receiver part R1 and the heterodyne receiver part R2. The reference frequency fR generated in the reference crystal REF can in the present case be multiplied in a multiplier MULT by a factor N to a suitable LO frequency and used in the first converting receiver part R 1.

In all the embodiments described above the lower frequency band has been processed in the heterodyne receiver part. The upper frequency bands have been converted to substantially the lower frequency band.

It is of course possible instead to convert signals in the lower frequency band to the upper frequency band and let the upper frequency band be received by the heterodyne receiver part. In such cases the sum frequency of an LO frequency and the received signal be selected at conversion of a signal in the lower frequency band to a signal in the upper frequency band. This implies, however, that radio signals in the lower frequency band are converted to the upper frequency band, thus generating an intermediate frequency. This may be less desirable if the object of generating an intermediate frequency is to convert the received radio signal down to a lower frequency.

Also, it is clearly seen that the LO frequencies generated by the device for generation of LO frequencies may also be used by a transmitter part in a combined transmitter/receiver in transmit mode. It is then possible to have either a directly modulated oscillator or a transmitter-mixer.