JPS6117420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an in-vehicle radio receiver.
The purpose is to improve reception characteristics.

When installing a C-tuned radio receiver using a barac diode in a car, problems such as tracking occur due to the car antenna's capacitance, as shown in the equivalent circuit in Figure 1, so it is necessary to change the antenna circuit to an untuned circuit. There must be. In the figure, R ₁ and C ₁ are the radiation impedance of the antenna, and C ₂ is the capacitance of the cable. Moreover, as a result, the practical sensitivity (S/N) is unavoidably worse than that of a μ-tuned radio receiver.

The present invention eliminates this drawback. First, S/N is the signal level supplied to the radio receiver.
It is determined by the square root of the source impedance seen by the radio receiver and the noise figure (NF) of the radio receiver. Therefore, if NF is constant, the S/N can be improved by increasing S/N∝A/√. Here, A is the signal level supplied to the radio receiver, and B is the signal source impedance seen from the radio receiver.

On the other hand, in Fig. 1, the impedance of the resistor R ₁ is sufficiently lower than that of the capacitor C ₁ , so if the input impedance of the radio receiver is sufficiently high, the signal level supplied to the radio receiver will be equal to that of the capacitors C ₁ and C ₂ . Determined by the division ratio. Also, the signal source impedance seen from the radio receiver becomes C ₁ +C ₂ , and this relationship is as shown in FIG.

Now, if an inductance L ₁ is inserted into C ₁ as shown in Figure 3, the signal level division ratio will become smaller due to series resonance near the resonance frequency, and the signal level supplied to the radio receiver will increase. The signal source impedance seen from the radio receiver is also reduced, making it possible to improve the S/N ratio.
FIG. 4 shows this state.

If this resonant frequency is set within the reception band, the maximum sensitivity will be greatly improved near the resonant frequency. However, there are also disadvantages, such as the risk of oscillation and the increased sensitivity difference between receiving frequencies that are far from the resonant frequency.

Fig. 5 takes this point into consideration, and a resonant circuit K having a resonant frequency that almost matches the resonant frequency of the antenna is provided in the bias circuit of the high frequency amplification transistor or field effect transistor T. I try to drop it.

Therefore, even if an antenna having a resonance point within the reception band is used, constant sensitivity can be obtained over the entire reception band.

As is clear from the above embodiments, according to the present invention, it is possible to maintain good band characteristics and achieve high sensitivity.

[Brief explanation of the drawing]

Figure 1 is an equivalent circuit diagram of a conventional automotive antenna.
Fig. 2 is its characteristic diagram, Fig. 3 is an equivalent circuit diagram of the improved antenna, Fig. 4 is its characteristic diagram, and Fig. 5 is a configuration diagram of the main parts of an in-vehicle radio receiver according to an embodiment of the present invention. It is. C ₁ , C ₂ ...capacitance, L ₁ ...inductance.

Claims (1)

[Claims] 1. An inductance is provided between the antenna body and the feeder line, and the total capacitance up to the input section of the radio receiver including the antenna and the above inductance enable resonance within the reception band, and resonance that almost matches the resonant frequency of the above antenna side. A vehicle-mounted radio receiver characterized in that a resonant circuit having a frequency is added to a high-frequency amplifier circuit, and reception sensitivity is reduced when the resonant circuit resonates.