JPH0510431Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an FM diversity receiving device suitable for use in a vehicle.

[Technical background of the invention and its problems]

Radio waves emitted from a transmitting antenna reach the receiving antenna through various routes. Since there is a time difference between the arrival of each of these radio waves,
Interference occurs between these multiple radio waves within the receiving device. For this reason, when receiving FM broadcasts while driving, significant distortion and noise may occur depending on the location.

FM diversity receivers are designed to reduce such interference, and there was a conventional FM diversity receiver as shown in Figure 2.

In the figure, 1 and 2 are FM receiving antennas, and 3 is a radio frequency (RF) that selects one of antennas 1 and 2.
4 is a front end that selectively amplifies the high frequency signal received by the antenna and converts it into an intermediate frequency (IF) signal; 5 is an IF amplifier circuit that amplifies the IF signal from the front end 4; 6 is the amplified IF signal. FM detection circuit that detects and outputs a composite signal; 7 is a comparator that compares the instantaneous value and average value of the S meter output corresponding to the received field strength from the IF amplifier circuit 5, and controls the RF switch 3 based on the result; The above instantaneous value is offset by ΔV from the average value.

In the above configuration, when one of the antennas 1 and 2 is selected by the RF switch 3, the instantaneous value exceeds the offset of ΔV and falls below the average value, as shown in FIG. When the instantaneous value falls, the output of the comparator 7 is inverted, and accordingly the RF switch 3 is switched to select the antenna 2, and thereafter the drop in the instantaneous value is monitored.

In this state, if an interference wave exists adjacent to the desired wave, the following envelope caused by the desired wave and the interference wave appears in the S meter output of the IF amplifier circuit 5.
cos(ω ₀ t+φ), and the interference wave is Acos(ω ₀ t+φ+φ')
,
where A is the relative level of interference to the desired signal,
If φ is the phase angle due to the modulating wave and φ' is the phase difference of the interference wave relative to the desired wave, an envelope occurs when the interference wave has the same frequency as the desired wave but is delayed or is an adjacent frequency, but all interference waves can be expressed by the above equation.

When the desired wave and the interference wave are combined, cos(ω ₀ t+φ) + Acos(ω ₀ t+φ+φ') = (1+Acosφ')・cos(ω ₀ t+φ)−Asinφ'
・sin(ω ₀ t+φ) =√(1+′) ² +(′) ²・
cos(ω ₀ t+φ+φ″) =√1+ ² +2′cos(ω ₀ t+φ+φ″
), where φ″=tan ^-1 (Asinφ′/1+Acosφ′).

Therefore, the S meter output is S=√1+ ² +
2Acosφ', and if we take A as a parameter and plot φ' on the horizontal axis, we get the result as shown in Figure 4, where the level A of the adjacent channel approaches 1 or the phase (2n+
1) When π (n=0, ±1, ±2...), the envelope drop is maximum.

The device configured as described above detects this drop in the S meter output and switches the antenna, so if the S meter output frequently drops due to interference waves or multipath, the antenna will be switched frequently. As a result, switching noise is superimposed on the composite signal,
As shown in FIG. 5, compared to a normal FM receiver, this system had the disadvantage that the two-signal selectivity deteriorated due to interference from adjacent channels. In Figure 5, the horizontal axis is the detuning frequency and the vertical axis is the input level of the interference wave.The interference wave level is plotted when the level of the interference wave becomes -30dB with respect to the output of the desired wave. There is.

[Purpose of invention]

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional receiver, and its object is to provide an FM diversity receiving device that prevents deterioration of two-signal selectivity when adjacent interference waves are present.

[Summary of the idea]

By controlling permission/disapproval of diversity operation using the output of a wideband AGC detection circuit that amplifies and detects intermediate frequency signals including adjacent interference waves from the front end, diversity operation is activated when the level of adjacent interference waves exceeds a predetermined value. The operation is stopped to prevent deterioration of the two-signal selectivity.

〔Example〕

Hereinafter, one embodiment of the FM diversity receiving device according to the present invention will be explained based on FIG.
Portions equivalent to those of the conventional device described above with reference to the figures are given the same reference numerals.

In FIG. 1, 10 is a wideband AGC detection circuit added according to the present invention, and this circuit receives a part of the RF signal or IF signal from the front end 4,
The input level including adjacent interference waves is amplified and detected to output a DC voltage, and when the input level exceeds a predetermined value, the DC voltage that rises is input to the comparator 7 as a comparison prohibition signal.

With the above configuration, the selectivity of the receiving device can now be increased.
If it is BdB, the adjacent interference wave that is input beyond BdB will be at almost the same level as the desired signal or higher, and the envelope of the instantaneous value of the S meter output signal will drop, causing frequent antenna switching. However, if comparison of the instantaneous value and average value in comparator 7 is prohibited when the input level exceeds CdB, frequent antenna switching will not occur and the antenna will be fixed to the one before comparison was prohibited. Furthermore, switching noise caused by frequent antenna switching can be suppressed.

Note that the input of the wideband AGC detection circuit 10 is
Since not only the adjacent interference wave but also the desired wave is input, even if there is no adjacent interference wave, when the desired signal exceeds a predetermined level, the comparison operation of the comparator 7 is prohibited, and the antenna is fixed. However, if the desired wave is at a predetermined level or higher, there is no need to switch antennas, so there is not only no problem in practice, but there is also a great advantage due to the use of a wideband AGC detection circuit that has a simple configuration and is inexpensive.

In addition, in the above embodiment, multiple antennas are used.
We have explained the case of switching diversity in which switching is performed via an RF switch, but it consists of multiple antennas and multiple receivers corresponding to each antenna.
The same effect can be obtained even if the present invention is applied to selection diversity in which the one with the maximum S/N is selected.

[Effect of idea]

As explained above, according to the present invention, by passing the intermediate frequency signal containing adjacent interference waves from the front end through the wideband AGC detection circuit, the adjacent interference waves are detected by the wideband AGC detection circuit and the diversity operation is stopped. Therefore, deterioration of the two-signal selectivity can be prevented with a simple configuration and at low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing an embodiment of the FM diversity receiving device according to the present invention, FIG. 2 is a circuit block diagram of a conventional device, and FIG. 3 is a diagram for explaining the general operation of the diversity device. , FIG. 4 is a graph showing changes in the S meter output of the IF circuit in FIG. 3 due to adjacent interference waves, and FIG. 5 is a graph for explaining problems with the conventional device. 1, 2...Receiving antenna, 3...High frequency switch, 4...Front end, 5...IF amplifier circuit,
6...FM detection circuit, 7...Comparator, 10
...Wideband AGC detection circuit.

Claims (1)

[Claims for Utility Model Registration] A plurality of antennas, a high frequency switch that selects one of the plurality of antennas, and a high frequency signal from the antenna selected by the high frequency switch that is selectively amplified and converted into an intermediate frequency signal. an intermediate frequency amplification and detection circuit that amplifies and detects an intermediate frequency signal from the front end; and a comparator that compares an instantaneous value and an average value of an output corresponding to the electric field strength of the intermediate frequency amplification and detection circuit. , an FM diversity receiving device that controls the high frequency switch using the output of the comparator, and a wide band capable of amplifying and detecting an intermediate frequency signal including adjacent interference waves from the front end.
An FM diversity receiving device, further comprising an AGC detection circuit, and an output of the wideband AGC detection circuit is used to control permission or disapproval of a diversity operation that controls the high frequency switch based on the output of the comparator.