JPS6412403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multipath signal generating device that is effective when analyzing FM multipath interference and considering countermeasures.

In general, the FM multipath phenomenon that occurs due to the reflection of radio waves from the topography and buildings around the receiver causes an extremely large deterioration of the playback quality, and the current
It is no exaggeration to say that this is the biggest problem with FM reception. However, it is difficult to obtain an equivalent phenomenon using a circuit for this multipath phenomenon, and therefore analysis and countermeasures cannot be left to the imagination. 2. Description of the Related Art Conventionally, as a multipath signal generating device, those shown in FIGS. 1 and 2 are known. In FIG. 1, 1 is a modulation signal generator, 2 is an FM signal generator,
3 is a coaxial cable, 4 is an attenuator, and 5 is a mixer, and the coaxial cable 3 realizes delay of the FM signal. However, this method requires a cable length of approximately 2 km to obtain a delay of, for example, 10 μS, making the device extremely large and also requiring compensation for signal attenuation due to the cable. Another problem was that it was almost impossible to make the delay time variable. FIG. 2 shows a means for delaying a low frequency modulation signal since it is difficult to delay at high frequencies. 2' is another FM signal generator set to the same frequency as FM signal generator 2, 6
is a low frequency delay device, and 7 is a reference frequency oscillator.
Here, the phase synchronization is performed by the reference oscillator 7.
FM signal generators 2 and 2' separately modulate delayed and non-delayed modulation signals, respectively, and expect the mixed result in mixer 5 to be a multipath signal. However, this method requires that the signal generators 2, 2' be phase synchronized externally, which makes the device expensive. In addition, although the two FM signal generators are statically synchronized in frequency and phase, at the time when modulation is actually applied, the way each FM signal generator applies modulation to the modulation signal (for example, modulation There was a problem that a true multipath signal could not be obtained due to differences in sensitivity and linearity.

The present invention provides an FM multipath signal generating device that has a simple configuration, can synthesize original multipath signals, and can set delay times with high precision. In other words, focusing on the fact that the FM signal is an analog signal but has a constant amplitude,
This is treated as a pulse waveform, and a monostable multivibrator is used as a delay element.
Monostable multivibrator is pulsed
Acts as a lossless delay element for FM signals,
Therefore, a large number of cascade connections are possible (a wide range of delay times can be accommodated). In addition, the maximum delay time per multivibrator circuit can be increased as the input frequency is lower, so FM with a center frequency that is low enough for a delay device using a multivibrator can be obtained.
An effective configuration is to provide a signal, combine the multipath signals, and then raise this signal to a high frequency that can be easily handled by the FM receiver.

The present invention will be described below with reference to drawings of embodiments. FIG. 3 is a block diagram showing an embodiment of the FM multipath signal of the present invention. In Figure 3, 4'
8 is an attenuator for the signal that is not delayed; 8 is a delay device composed of a plurality of monostable multivibrator circuits; and 9 is a frequency converter. Since the FM signal originally has a constant amplitude, it is possible to pass it through a digital circuit, whereas monostable multivibrator circuits, by connecting them in series, delay the digital signal by the output pulse time width per circuit and transmit it. be able to. Now, if the output frequency of the FM signal generator is 500KHz, one period is 2μS, so it is possible to obtain a delay of up to 2μS per monostable multivibrator stage. In reality, it is appropriate to set it to about 1 μS, considering the modulation and margin. The reason for installing the attenuator 4' is to realize such a situation, since in an actual field, the level of the direct wave may be lower than that of the reflected wave. The output signal of the mixer 5 is outputted by the frequency converter 9 at the intermediate frequency of the FM receiver, 10.7 MHz, or at a suitable frequency within the receiving band (76 to 90 MHz in Japan) and given to the receiver.

Next, an example of the configuration of the delay device 8 is shown in FIG. In the figure, 10 to 13 are 10 μS delay units each having a plurality of monostable multivibrator circuits connected in series to obtain a delay time of 10 μS, 14 to 22 are 1 μS delay units to obtain a delay time of 1 μS, and 23, 24
is a signal selector, and by switching the signal selectors 23 and 24, it is possible to set the delay time from 1 to 49 μS in 1 μS increments. 10μS delay unit 10~
By adding 13, the maximum delay time can be easily set. In the above explanation, the signal to be delayed is one system, but the delay device 8 and attenuator 4 are independent.
By adding the FM signal generator 2 and the mixer 5 in parallel, it can be easily extended to a multi-signal multi-path signal generator.

As described above, according to the present invention, by using a monostable multivibrator circuit in the delay device,
It is possible to realize a small multipath generator with a simple configuration and easy delay time setting.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a conventional FM multipath generator, FIG. 3 is a block diagram showing an embodiment of the FM multipath signal generator of the present invention, and FIG. 4 is a delay circuit of the same device. FIG. 2 is a block diagram showing an example of the configuration. 1... Modulation signal generator, 2... FM signal generator, 4, 4'... Attenuator, 5... Mixer, 8...
Delay device, 9...frequency converter.

Claims (1)

[Claims] 1. An FM signal generator, a delay device consisting of a plurality of cascaded monostable multivibrators that delay the output signal of the FM signal generator, and an input signal of the delay device. a first attenuator and the FM
a second attenuator to which the output signal of the signal generator is input; a mixer to which the output signals of each of the first and second attenuators are input; and an output signal of the mixer to be input to the intermediate frequency of the FM receiver. Alternatively, it is possible to provide a frequency converter for converting to a frequency within the reception band, and set the output frequency of the FM signal generator to be sufficiently lower than the output frequency of the frequency converter, thereby increasing the amount of delay per circuit of the multivibrator. An FM multipath signal generator characterized in that it is configured as follows. 2 The delay device consists of N delay units that obtain a delay of 10 μS by connecting monostable multivibrator circuits in series, and a delay unit 9 consisting of a single or multiple monostable multivibrator circuits that obtain a delay of 1 μS.
2. The FM multipath signal generating device according to claim 1, wherein the FM multipath signal generating device is configured such that a maximum of (10·N+9) μS can be set in 1 μS increments by combinations of FM multipath signals.