JP3121748B2 - Receiving frequency selecting method, receiving frequency selecting circuit, receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a circuit for selecting a reception frequency when frequency diversity reception is performed on an HF line, and a receiving apparatus having the circuit.

[0002]

2. Description of the Related Art In frequency diversity reception using an HF line, switching to an optimum reception frequency is automatically performed when the state of a received signal deteriorates due to the state of the ionosphere. FIG. 2 shows a configuration example of a conventional frequency selection circuit for that purpose, in which received waves 1 and 2 (HF signals) from two antennas (not shown) for space diversity are converted into frequency switching circuits 11 and 21. Respectively. In each of the received waves 1 and 2, a plurality of radio frequency signals are modulated and transmitted with the same information for frequency diversity, but the frequency switching circuits 11 and 21 transmit the frequency signals from the signal level determination circuit 4. By the switching signals 14 and 24,
Radio frequency signals of the reception waves 1 and 2 whose reception level is equal to or higher than a predetermined threshold are extracted and demodulated by the demodulation circuits 12 and 22.
To each. The demodulated signals demodulated from the HF signals by the demodulation circuits 12 and 22 are input to level detection circuits 13 and 23, respectively, and the reception levels are detected, and their detection outputs and the demodulation signals from the demodulation circuits 12 and 22 are both diversity. Input to the circuit 3.

Here, the level detection in the level detection circuits 13 and 23 is performed, for example, assuming that the demodulated signal is a pulse signal, performing integration for each bit, and setting the magnitude as a reception level.

The diversity circuit 3 includes demodulation circuits 12, 2
Out of the demodulated signals output from the
The signal with the higher reception level output from 3, 23 is an output signal. If the demodulation signal is a pulse signal and the reception level is output from the level detection circuits 13 and 23 for each bit, the reception level is determined for each bit and the demodulation signal is switched.

[0005] The level determination circuit 4 comprises a level detection circuit 1
Receiving the reception levels output from the reception circuits 3 and 23 via the diversity circuit 3, it is determined whether the lower one of the two reception levels is equal to or less than the threshold. This threshold value is defined as a reception level below which communication becomes impossible.
When it is determined that the lower level is lower than the threshold value, a frequency switching signal for switching the frequency of the received wave having the lower level is output. The frequency of the received wave is switched in this manner, and the detection of the received level, the level determination, and the frequency switching are repeated until the received level becomes equal to or higher than the threshold.

[0006]

FIG. 3 is a block diagram of FIG.
Shows an operation example of the reception frequency selection circuit at time t ₀
Reception level R2 of the received wave 2 is below the threshold value L _th, the switching of the frequency f ₂ which has been selected until then began. Assuming that the switching order is set in a fixed order of f ₁ → f ₂ ..., The frequencies f ₂ to f ₃ , f ₄
...... sequentially switched to, the switching is continued until the reception level R2 exceeds the threshold value L _th. In FIG. 3, the frequency f _9
Shows the case where R2> Lth for the first time and the switching is completed. Thus, before time t ₂ when the reception level of the received wave 2 is recovered, as it is shown at time t ₁ in FIG. 3,
Below the level R1 also the threshold L _th reception wave 1, the demodulated signal at this time becomes unreceivable state. If the switching time when the reception level falls below the threshold is shortened, the probability that the above two systems become below the threshold is reduced.However, if the switching time is too short, the reception state at the frequency after switching is ensured. In such a case, it becomes difficult to make a decision, and a problem such as the necessity of the next switching immediately occurs, and a stable circuit cannot be realized.

SUMMARY OF THE INVENTION An object of the present invention is to provide a receiving apparatus which can perform selection (switching) of a receiving frequency when a received signal condition is deteriorated in a short time and accurately when performing frequency diversity reception on an HF line. It is an object of the present invention to provide a frequency selection method and a circuit thereof, and a receiving device provided with the circuit.

[0008]

SUMMARY OF THE INVENTION According to the present invention, when the same information is transmitted as a plurality of radio frequency signals having different frequencies, it is received and has a reception level higher than a predetermined threshold from the reception wave. In a receiving frequency selecting method of a receiving apparatus for performing a receiving process by selecting one of the radio frequency signals, a frequency at which each of the radio frequency signals is selected is stored in a memory, and the radio frequencies are stored in descending order of the stored frequency. Determine the switching order of the frequency signal, when the reception level of the selected radio frequency signal is lower than the threshold,
A method of selecting a reception frequency, comprising switching radio frequency signals in the switching order until the reception level exceeds the threshold, is disclosed. Further, the present invention provides frequency switching means for selecting one radio frequency signal from a reception wave composed of a plurality of radio frequency signals having different frequencies modulated by the same information, and a radio frequency signal selected by the means. A level detection unit for detecting a reception level; and a level determination unit for outputting a switching signal to the frequency switching unit when the reception level detected by the unit is equal to or less than a predetermined threshold. In the frequency selection circuit, a memory for storing the frequency at which each of the radio frequency signals is selected by the frequency switching means, and a switching order determined in descending order of the frequency stored in the memory; Switching for controlling the frequency switching means so as to sequentially switch the radio frequency signal in accordance with the switching order each time a switching signal is output It discloses a receiving frequency selecting circuit, characterized in that a and control means.

[0009]

In each spatial path, there is often a correlation between the frequency of the radio frequency signal and the probability of occurrence of fading. Therefore, the more frequently the radio frequency signal of the frequency selected is, the smaller the probability that the reception level is below the threshold value is. For this reason, by switching in descending order of the frequency stored in the memory, the required switching time can be reduced on average. Further, when the frequency selected for each time zone is stored and the switching control is performed according to this frequency, the required time can be shortened in a case where the fading occurrence probability has a correlation with the time zone.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. FIG. 1 is a block diagram showing an embodiment of a reception frequency selection circuit according to the present invention. In FIG. 1, a switching control circuit 5, a memory 7 and an hour meter 6 are added to the conventional circuit of FIG.
Are input to the switching control circuit 5. In this configuration, the operations of the circuits having the same names and the same reference numerals as those in FIG. 2 are also the same as those in FIG. I do.

The memory 7 has a table corresponding to each of the received waves 1 and 2. FIG. 5 illustrates a table 62 corresponding to the reception wave 2, and a table corresponding to the reception wave 1 is provided in the same manner. It is assumed that the memory 7 is a non-volatile memory that is backed up even if the power of the device is turned off, and that can save the contents without erasing. The contents of the table 62 indicate that the frequency selected as having reached a level equal to or higher than the threshold value which is a receivable level in the corresponding receiving system is determined for each frequency f ₁ , f ₂ ,... And for each time zone B1, B2,. … For each one. In this table, the reception level of the received wave falls below the threshold, and the frequency is switched by the frequency switching signal 14 or 24 from the level determination circuit 4, whereby the reception level of the receiving system exceeds the threshold and the frequency switching stops. Then, the frequency is updated by incrementing the value of the time zone including the time indicated by the hour meter 6 from the frequency of the frequency at that time.
Note that the time periods B1, B2,...
Set the time width to about an hour.

The above-described tables are provided in the memory 7 for each receiving system, and the switching control circuit 5 performs control as follows. FIG. 4 shows an example of the operation.
Assuming that the level of the received wave 2 is reduced at time t ₃ belonging to and the frequency switching signal 14 is output from the level determination circuit 4, the switching control circuit 5 looks at the above-described table 62 and has selected it up to now. A command to select the frequency with the highest frequency in the time zone including the time from among the frequencies other than the frequency (referred to as f ₂ ) is output to the frequency switching circuit 21. In this case the frequency f ₅ is selected in the example of FIG. As a result, when the reception level of the reception wave 2 has not yet exceeded the threshold value, a command to select a frequency having the next magnitude other than f ₂ and f ₅ in the time zone B2 is output to the frequency switching circuit 21. I do. In the example of FIG. 5, this time the frequency f ₉ is selected.

In general, a frequency that is easily attenuated by facing often correlates with the position of an antenna or a time zone. Therefore, the higher the selected frequency, the higher the probability of improving the reception level. Therefore, if the frequency switching order is determined based on the selected frequency as in the present embodiment, the switching time can be reduced on average on average compared to the conventional frequency switching in a fixed order. 4, the reception level can be recovered with a small number of switching operations. Therefore, when the level of the used system decreases at time t ₄ in FIG. 4, the probability that the demodulated signal can be maintained in a receivable state by switching to the standby system is also improved.

The level judging circuit 4 judges whether or not the lower receiving level has become equal to or less than a threshold value, as in the diversity circuit 3 when the receiving signal is a pulse. In a short-time determination such as when viewed in 1-bit units, frequency switching frequently occurs, and circuit operation becomes unstable. For this reason, the level determination circuit 4 makes a determination by comparing an average reception level of, for example, about 5 minutes with a threshold.

According to the present embodiment, the frequency can be switched in a short time when the reception level is reduced, and the time required for the demodulated signal to become unreceivable can be reduced. In the above embodiment, the case where two receiving systems are used has been described as an example. However, the same effect can be obtained by applying the present invention even when one receiving system or three or more receiving systems are used. There is.

[0016]

According to the present invention, when frequency diversity reception is performed on an HF line, the reception frequency can be selected (switched) in a short time and accurately when the reception signal condition deteriorates. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a reception frequency selection circuit according to the present invention.

FIG. 2 is a block diagram illustrating an example of a conventional reception frequency selection circuit.

FIG. 3 is a diagram illustrating an example of a frequency switching operation by the circuit of FIG. 2;

FIG. 4 is a diagram illustrating an example of a frequency switching operation by the circuit of FIG. 1;

FIG. 5 is an explanatory diagram of a frequency table provided in a memory circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Received wave 2 Received wave 3 Diversity circuit 4 Level judgment circuit 5 Switching control circuit 6 Hour meter 7 Memory 11 Frequency switching circuit 12 Demodulation circuit 13 Level detection circuit 14 Frequency switching signal 21 Frequency switching circuit 22 Demodulation circuit 23 Level detection circuit 24 Frequency Switching signal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 7/00 H04B ⁷ /02-7/12 H04L 1/02-1/06

Claims (7)

(57) [Claims] When the same information is transmitted as a plurality of radio frequency signals having different frequencies, it is received and one of radio frequency signals having a reception level equal to or higher than a predetermined threshold is selected from the received waves. In the receiving frequency selecting method of the receiving apparatus that performs the receiving process, the frequency at which each of the radio frequency signals is selected is stored in the memory, and the switching order of the radio frequency signals is determined in descending order of the stored frequency, When the reception level of the selected radio frequency signal falls below the threshold value, the radio frequency signals are switched in the switching order until the reception level exceeds the threshold value. Selection method. 2. The frequency is obtained by dividing a day into a plurality of time zones, storing the frequency in the memory as a frequency selected for each of the time zones, and determining whether the level of the selected radio frequency signal is high. The method according to claim 1, wherein when the frequency is lower than the threshold, the switching order is determined using the frequency of the time zone to which the lower time belongs. 3. The receiving apparatus according to claim 1, wherein the frequency of each radio frequency signal stored in the memory is updated by adding +1 each time the radio frequency signal is selected. How to select the receiving frequency. 4. A frequency switching means for selecting one radio frequency signal from a reception wave composed of a plurality of radio frequency signals having different frequencies modulated by the same information, and a radio frequency signal selected by the means. Level detection means for detecting a reception level; and level determination means for outputting a switching signal to the frequency switching means when the reception level detected by the means is equal to or less than a predetermined threshold value. In the frequency selection circuit, a memory for storing the frequency at which each of the radio frequency signals is selected by the frequency switching means, and a switching order determined in descending order of the frequency stored in the memory; A switch for controlling the frequency switching means so as to sequentially switch the radio frequency signal in accordance with the switching order each time the switching signal is output. Receiving frequency selecting circuit, characterized in that a control means. 5. The memory stores the frequency as a frequency that is obtained by dividing one day into a plurality of time zones and a frequency selected for each of the time zones. The frequency switching control is performed for each band, and the switching of the frequency is performed using the switching order defined for a time zone to which the output time belongs every time a switching signal is output from the level determination unit. 5. The reception frequency selection circuit according to 4. 6. The switching control means has a function of updating the frequency of each radio frequency signal stored in the memory by +1 each time the radio frequency signal is selected. Item 6. The reception frequency selection circuit according to item 4 or 5. 7. A receiving apparatus comprising the receiving frequency selecting circuit according to claim 4. Description: