CN1273714A

CN1273714A - AM quality detector

Info

Publication number: CN1273714A
Application number: CN99800343A
Authority: CN
Inventors: M·J·J·G·费尔海登
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 1998-03-26
Filing date: 1999-03-08
Publication date: 2000-11-15
Also published as: KR20010012983A; WO1999049581A2; WO1999049581A3; EP0995273A2; JP2002500850A

Abstract

During an automatic scanning of an AM frequency band it is required that the scanning is only stopped when a usable audio signal is received. To achieve this normally the receiver checks the (RF) signal level and the IF frequency of the received signal. Because at night the propagation of AM signals is improved as a consequence of the weather conditions it is possible that a far away station having the same transmitting fequency interferes with a local station. To overcome this a detector and receiver are proposed whereby the detector detects interferences of two or more stations and supplies a detection signal resulting in resuming scanning for a next station.

Description

The AM property detector

The present invention relates to a kind of receiver described in the preorder of claim 1.

The invention still further relates to a kind of detector that in this receiver, uses.

The invention still further relates to the method that is used to scan frequency band described in the preorder of claim 5.

What this receiver and method were known in the art also is used in the prior art.

Receiver with the device that is used to overcome the mutual interference problem of adjacent channel/platform also is known.For example, International Patent Application WO 97/23959 has been described such receiver.

During scanning an AM frequency band automatically, described receiver is checked (RF) signal level and the IF frequency of received signal.On this basis, whether its decision has received spendable AM signal.If then this signal is further processed and offers (or a plurality of) loud speaker of described receiver.If not, then utilize a predetermined value to change described frequency and this new signal is repeated identical inspection.

The transmitter frequency of AM platform is selected in the mode that causes their mutual least interference usually.But, this only by day during effectively.At night, because ionospheric ionization marked change and moisture inversion takes place, thereby the remarkable improvement of propagation caused.This will cause by day can not received long distance destage strong reception.Because these long distance destages can not be received under normal operation, they can use the transmitter frequency identical with near transmitter.This is not in-problem by day, and still, at night, these long distance destages can cause the main interference to local station.These interfering frequencies are referred to as beat frequency.At automatic searching period, under the situation of such platform of will jumping, these interference can reach the degree that makes described can't use.

The shortcoming of known receiver be checked signal level and IF frequency and determine they be operable after, described signal also will be further processed and offer (or a plurality of) loud speaker.Like this, the interference that is not detected can cause the signal that is provided that is unsuitable for reappearing described audio signal.

The purpose of this invention is to provide a kind of receiver and a performance that does not have the detector of prior art shortcoming and further improve described receiver.For this purpose, first aspect of the present invention provides a kind of receiver as claimed in claim 1.Second aspect of the present invention provides a kind of detector as claimed in claim 4.The 3rd aspect of the present invention provides a kind of method that is used to scan frequency band as claimed in claim 5.

When the available AM of (automatically) search radio station, when finding an operable radio station, preferably described receiver only stops search.Promptly have operable RF frequency, be higher than the signal level of a predetermined value and do not disturb (particularly night) with other radio station of for example long distance destage.This is to utilize receiver according to the present invention to be used for detecting a detector that whether has received two (or a plurality of) signals with (approaching) same transmit unit frequency by use to realize.When described detector detected an interference, this detector offered described processor to restart scanning of next radio station with a detection signal.

Owing to be privately owned in all AM radio station of the U.S. at present, they use the transmitter (comparing with the radio station that (at present) European platform (they use the atomic clock with frequency dependence) has) that utilizes crystalchecked.Reception will cause producing about 0-40Hz in receiver when the result of Chan Shenging is (having the same transmit frequency) two U.S. AM radio station therefrom, amplitude approximately is the beat frequency of normal modulation twice.This beat frequency can be used to obtain the multipath reception of some valuably by described detector.

Particularly under the condition of the U.S. (other country that perhaps has similar transmitter condition), this system is to providing great improvement aspect the search automatically at the AM at night.

Because described AM performance is inspection after described signal level and IF frequency are examined, so, can not reduce search speed.

Described detector can use minimum cost to be affixed on the existing AM receiver.

Should illustrate that according to European patent application EP-A-0410663, the receiver that is used to receive the signal of a which amplitude modulation with higher and low sideband has been known.Described receiver comprises that also one is used for providing being illustrated in and modulated higher does not wish that than the lower sideband audio signal property detector of the higher of noise and lower-performance signal and the described performance signals of response are to a described selector higher and that handle to have the audio output signal that has reduced noise to provide than the lower sideband audio signal.

An embodiment according to receiver of the present invention has the described characteristic of claim 2.

Approximately the beat frequency of 0-40Hz can use the back to follow to be useful on generation to detect as the detection signal and the low pass filter with 40Hz cut-off frequency of an amplifier/rectifier that is proportional to the dc voltage of interference volume.

Comprise the described characteristic of claim 6 according to one embodiment of the method for the invention.

Triggered by a single bursts of error for fear of described detector, further improved the operation of described method by measuring the predetermined space that exists between them more than once.

By the description below in conjunction with the referenced drawings example, the present invention and can selecting arbitrarily uses the bells and whistles of carrying out advantage of the present invention will become more obvious.Described accompanying drawing is:

The block diagram of Fig. 1 show according to example of receiver of the present invention and

The block diagram of Fig. 2 shows an example according to AM property detector of the present invention.

The block diagram of Fig. 1 shows the example according to a radio receiver RR of the present invention, and this receiver has an antenna input AI who is used to receive the RF signal.One is used for described RF signal and the mixer unit MIX that mixes and provide the IF signal from this machine oscillator signal Slo of oscillator unit VCO.This IF signal is provided for and is used to amplify described IF signal and detects AM signal and the AM unit that (unfiltered) AM signal LF is provided.Described AM unit offers processor unit PROC with signal level V1 and frequency signal FIF, and this processor unit offers oscillator VCO with a signal.When described signal level V1 and/or IF signal are not in predetermined range value, processor unit PROC for example will offer described oscillator unit to the voltage signal of (newly) to revise described machine oscillator signal during scanning automatically.The output of described AM unit is coupled to an audio unit AU, so that the AM signal LF of non-filtered is done further processing and treated signal is offered loud speaker LS.

Described processor unit also comprises a device that is used for scanning automatically (search) frequency band.In this example, this can be by provide the voltage of one higher (or lower) to realize to described oscillator unit (after this will directly be referred to as voltage-controlled oscillator (VCO)) at every turn.

Radio receiver RR according to the present invention comprises that also is used to detect an AM property detector AQD (seeing the detailed description of Fig. 2) who whether receives an available AM signal.So carry out to disturb and check.Described AM Performance Detection receives the AM signal LF of non-filtered.Because otherwise described interference will (at described audio unit (AU) for example afterwards) be filtered, so this is necessary.

In order to (automatically) searching period of obtaining AM radio station preferably when finding an operable radio station, described receiver preferably only stops search.Promptly have an available RF frequency, good signal level and do not disturb (particularly at night) with the long distance destage.This is to utilize receiver according to the present invention whether to be used to detect the described AM property detector that has identical (approaching) transmitter frequency from these two (or a plurality of) received signals by use to realize.When described AM property detector detected an interference, this AM property detector offered described processor unit PROC with detected signal AMq1, so that restart to be used for scanning of next platform.

Because all be privately held in the U.S. described AM radio station at present, they use the transmitter (comparing with present the use with the country that Euroradio was had of atomic clock as benchmark) of crystalchecked.The result who does like this is received in when being two (having the same transmit frequency) U.S. AM radio station and produces about 0-40Hz in the receiver, amplitude approximately is the beat frequency of normal modulation twice.Utilize described detector, described beat frequency can be by the multipath reception of the some that preferentially is used to obtain.

Fig. 2 shows the example of an AM property detector AQD2 in further detail.Described AM property detector receives the AM signal LF2 of non-filtered at its input, and this signal for example is provided for that cut-off frequency is the low pass filter LPF2 of 40Hz, with the signal component (promptly disturbing) that only obtains to be lower than 40Hz.By filtering the signal that is higher than 40Hz, avoided described AM property detector to act on again on the AM audio signal of (quite) low frequency.This signal is exaggerated in amplifier AMP2.The output of described amplifier is coupled to for example to be used to set up the DC level and to detect and is lower than the signal value of 40Hz and detected signal AMql2 is offered described processor unit (PROC, see Fig. 1) checkout gear DET2, described processor unit will determine whether to receive a spendable AM signal on the basis of the detection signal AMq12 of institute.

Select the cut-off frequency of about 40Hz to measure normal audio signal to avoid described AM property detector.Owing to need reduce fast to avoid described AM property detector to detect low-frequency audio signal, so four utmost point filters are best.

In order further to improve the operation of described AM property detector and receiver, utilize a predetermined space more than once, for example the measurement of detection signal is carried out at the interval of three times and 20ms.

If the signal of two transmitters has unlike signal intensity, the sensitivity of described AM property detector preferably reduces.The difference of the signal that antenna received is big more, and it is many more that the sensitivity of described AM property detector can be reduced.Since when two radio station approaching to have the strongest when being received on other same transmit frequency of big difference in signal strength will be better than more weak one, so this wishes.Like this, the strongest radio station will utilize more weak radio station to produce the audio frequency with minimum audio distortion.Therefore, should do not skipped in the automatic such radio station of searching period.

In addition, when described receiver is tuned to a radio station, as the result of tuning step, described AM property detector may provide a detection signal.This detection signal is directly proportional with the signal level of described receiver signal.As a result of, described AM property detector will point out mistakenly that a signal disturbed, that can not use is received and should restarts to be used for scanning of (follow-up) platform.

In order to overcome this shortcoming, can obtain a hardware solution.But this need increase a link between so-called front end and so-called IF/AM detector (AM unit).Because will occur between the different elements of described receiver that thereby cross interference causes screaming, instability or mistake, so this link is undesirable.

So, preferably obtain a kind of software solution of using software algorithm.When during automatic retrieval, finding a radio station, at first check described signal level (V1) and if when finding that this level is higher than a predetermined value, check described IF frequency (FIF).When finding that described IF frequency is also in the IF window of being asked, measure described AM performance (AMq1).Because the signal level by tuning post at that is known, so, can be proportional to this level and carry out a delay.Then, for example for example three measurements are carried out in this delay with the interval of 20ms.The mean value of this measurement will be equal to or higher than a set-point.Because this directly proportional delay makes a undesirable pulse (because the reception radio station that is tuned to) have time enough and is reduced before at the described AM performance measurement of execution (disturb and check).When the antenna signal increased, the short delay and the described delay that are used for the miniature antenna signal were performed longlyer.Use can not selected described delay to do not wish the measurement of pulse shape in various antennas input.

Owing to after checking described signal level and IF frequency, read described AM performance, so can not reduce search speed.

In addition, when the signal level of a signal in two signals is considered to signal level less than the another one signal, occupy ascendancy owing to have the received signal of strong signal level, so the Operational Figure Of Merit of described AM property detector (disturb and check) is lowered.

In the superincumbent description, idea of the present invention has been described on the basis of specific embodiment.Those of ordinary skill in this professional skill field can be made the difference that much falls into the scope that the present invention relates to and be changed.

Various square frames in the accompanying drawing can utilize and separate or the integrated circuit formation, also can carry out in the digital circuit of for example digital signal processor (for example processing unit PROC among Fig. 1).

The invention provides and use the AM property detector to overcome in untapped radio station, particularly to stop to scan automatically a kind of receiver of (search) problem, a kind of detector and a kind of method at night.

Be higher than after a minimum levels and described IF frequency fall within the preset frequency window in the described AM signal level of decision, described AM property detector detects whether there is interference.This interference causes than the detection signal in the low-frequency range (for example 0-40Hz), and this detection signal is used to restart to be used for the search in next radio station by described processing unit.

Claims

1. receiver, comprise the mixer unit that is used to receive the RF signal, be coupled to the oscillator unit of described mixer unit, be used for receiving IF signal and the AM unit that is used to amplify and detect an AM signal from described frequency mixer, an audio unit and a processing unit that is coupled to described AM unit and described oscillator unit and is used to control described oscillator unit that is used to handle described AM signal and is used for output signal is offered speaker, described processing unit also comprises a device that is used for scanning automatically frequency band, it is characterized in that described receiver comprises that one is coupled to the output of described AM unit and is used to detect a detector that is received the interference between the input signal and is used for providing to described processing unit detection signal at least two with approximate same frequency.

2. receiver according to claim 1 is characterized in that described detector comprises a low pass filter that is used to leach described AM signal.

3. receiver according to claim 2 is characterized in that described detector comprises a rectifying device that is used for the filtered signal of rectification and described detection signal is provided.

4. described detector that in receiver, uses according to claim 1.

5. method that is used for scanning an AM frequency band at receiver, have and utilize a predetermined value to change the step of described frequency at every turn, check the step whether receive a signal, comprise that also the step of checking a signal level, the step of checking the IF frequency and decision stop the step that scans or restart to scan, it is characterized in that after checking described signal level and IF frequency, carry out one and disturb the inspection step, comprise the AM signal of a non-filtered of low-pass filtering and obtain a detection signal, and whether decision stops the search to a radio station.

6. method according to claim 5 is characterized in that according to the signal value that is received, and after carrying out the interference inspection and determining whether to stop to scan, determines a delay.

7. method according to claim 5, the predetermined space amount that it is characterized in that disturbing the number of times of inspection to equal between them, to exist.

8. method according to claim 5 is characterized in that the signal value difference of the signal of reception is simultaneously depended in the sensitivity of described interference inspection.