JPS5923637A - Antenna tuning circuit for car am and fm radio receiver - Google Patents

Abstract

PURPOSE:To obtain a tuning frequency superior in rejection of interference wave removal characteristics, by providing antenna tuning circuits which use varactor diodes for AM and FM very closely to an antenna and obtaining the tuning frequency having sufficient tracking with a reception side. CONSTITUTION:The tuning circuits 4 and 5 which use the varactor diodes 10 and 13 for AM and FM are provided very closely to the antenna 1. Consequently, antenna serial capacity in the AM band and parallel capacity by a coaxial feeder are obtained and the influence of the latter is nearly eliminated to perform tuning while the entire AM band is covered within the variable capacity range of a varactor diode put on the market. On the other hand, transmission loss exerting influence upon the SN ratio of a low-level signal is reduced even in the FM band.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna tuning circuit for use in automotive AM and FM radio receivers that uses a variable capacitance diode as a tuning element. The present invention provides an excellent antenna tuning circuit which is connected between the antenna and the input terminal, and which selects a weak signal generated by the antenna described in item 1 and supplies it to the AM or FM radio receiver.

In general, in-vehicle AM and FM radio receivers are configured to receive both AM and FM with a single whip antenna to simplify the configuration, and the weak signals obtained from the antenna are sent to a single coaxial feeder. AM is placed near the driver's seat via electric wires.

The receiver is configured to supply an FM radio receiver.

In such a configuration, as is well known, the antenna in the AM band is expressed by the series equivalent capacity (15PF in JIS), and the parallel equivalent capacity of the coaxial feed line (JIS:
65PF) is added for I8, so it is not possible to sufficiently cover and tune the entire AM broadcast wave band by simply connecting a tuning circuit using a variable capacitance diode between the antenna and the input section of the receiver. This is difficult within the variable capacitance range of current variable capacitance diodes (usually about 20 to 450 PF), and conventionally they are generally coupled in an asynchronous manner. Therefore, the interference wave rejection characteristics and signal-to-noise ratio are inferior to those of conventional mu-tuning type vehicle-mounted AM receivers.

On the other hand, for FM, the equivalent circuit of the antenna in the FM band is replaced with an equivalent resistance of about 50Ω, so matching between the antenna and receiver can be achieved relatively easily using a coaxial feed line, and it is still possible to configure a tuned circuit. However, it becomes impossible to ignore the transmission loss due to the coaxial feeder line, and there is a problem that the signal-to-noise ratio in areas with weak electric fields deteriorates significantly. As a means to overcome these drawbacks, a band filter and an amplifier exclusively for the AM and FM bands were provided between the common antenna for receiving AM waves and FM waves conventionally installed in automobiles and the AM and FM radio receivers. There is a method of inserting an antenna band amplification circuit. However, with this method, it is possible to improve the signal-to-noise ratio in the case of weak signals by using amplification elements with a small noise figure, but since it is a broadband filter, the filter exists close to the receiving frequency. There have been problems in that it is impossible to eliminate second-second harmful waves, the characteristics for eliminating interference waves such as cross-modulation interference or intermodulation interference deteriorate, and the configuration becomes extremely complicated.

The present invention is intended to eliminate these drawbacks, and is to provide an antenna tuning circuit using a variable capacitance diode for AM and FM in the close vicinity of the antenna, and to supply the tuning control voltage of this tuning circuit from the receiver side. By doing this, it is possible to obtain a tuning frequency that is sufficiently tracked with the receiver side. Therefore, according to the present invention, a vehicle-mounted A with excellent interference rejection characteristics or signal-to-noise ratio
M, FM radio receiver can be provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An antenna tuning circuit for AM and FM radio receivers according to the present invention will be described below with reference to drawings of embodiments.

FIG. 1 shows an AM including the antenna tuning circuit of the present invention.

1 is a block diagram of an embodiment of an FM radio receiver.

The signal received by antenna 1 in FIG.
Branched into FM wave and AM wave signals by a splitter 3,
The output signals are applied to an FM antenna tuning circuit 4 and an AM antenna tuning circuit 5 which have variable capacitance diodes as tuning elements, and their output signals are mixed with each other by a mixer 6.
It is output to the output terminal 7 of the FM antenna tuning circuit 2o. This output signal is applied to the input terminal 22 of the AM and FM radio receiver via the coaxial feed line 21, and is separated into FM and AM signals by the splitter 23, and each signal is sent to the FM receiver 24 and the AM receiver 26. Added. Then, the tuning control voltage from the tuning control voltage generator 26 is applied to all the FM and AM tuning variable capacitance diodes (including, for example, the oscillation stage resonant circuit) of the FM receiver 24 and the AM receiver 26, and Via the coaxial feeder line 21, -''
It is supplied to each of the iiJ variable capacitance diodes of the FM antenna tuning circuit 4 and the AM antenna tuning circuit 5 that constitute the antenna tuning circuit 2o.

FIG. 2 is an electrical wiring diagram of a specific embodiment of the antenna tuning circuit 20 of the present invention.

In FIG. 2, capacitors 8 and 16 and inductances 9 and 17 are used to constitute the duplexer 3 and mixer 6 described above, and the value of capacitor 8.16 is AM
It is set to a value that blocks band signals and allows FM band signals to pass through without loss. On the other hand, inductances 9 and 17 are set to values that block FM band signals and allow AM band signals to pass through without loss.

Each variable capacitance diode for FM and AM still 10.
13. Each coil/L/11115 for FM and AM constitutes each antenna tuning circuit 4.6 for FM and AM, and the tuning control voltage from the receiver described above is applied via the resistor 19. It is supplied to each variable capacitance diode 10.13, and antenna tuning with sufficient tracking with the receiver side can be obtained. In addition, 12.14 is a bypass capacitor,
This is a capacitor with sufficiently low impedance in the 18id AM band.

- In the practical example, the outputs of the FM and AM antenna tuning circuits 4 and 6 are connected to the FM and AM coils/L'1
The output from the 1.15 tap position is a tap that matches the characteristic impedance of the coaxial feed line 21. Then, the connection between the antenna 1 and the antenna tuning circuit 20 is made sufficiently short, or the connection between the antenna 1 and the antenna tuning circuit 20 is
If it is made into an integral structure, the above-mentioned drawback, that is, the influence of the parallel equivalent capacity of the coaxial feeder line 21 in the AM band will be eliminated,
Since only the series equivalent capacitance of the antenna is required, it becomes possible to sufficiently cover the entire band using variable capacitance diodes currently available on the market. - Transmission loss caused by the coaxial feeder line 21 is also reduced for the 10,000 FM band. Output impedance of output terminal 7 of Ushida antenna tuning circuit 20 and input terminal 2 of receiver
At the time of reception, it is desirable that the two-dimensional impedance be set equal to the characteristic impedance (for example, 60Ω) of the coaxial feeder line 21.

As described above, according to the present invention, since a tuning circuit using a variable field 111 diode for AM and FM is provided in the close vicinity of the antenna, the antenna series capacitance in the AM band and the parallel equivalent due to the coaxial feed line are Among the capacitances, it is possible to almost eliminate the influence of the latter, and the AM
It is possible to cover the entire band and tune, while F
Even in the M band, it is possible to reduce the transmission loss that greatly affects the signal-to-noise ratio during weak signals, which is extremely advantageous in practice. AM, to the AM, FM common coaxial feed line, which is still coupled to the output end of the AM, FM tuning circuit.
When the tuning control voltage that performs tuning control in the FM receiver is superimposed and supplied to each iiJ variable capacitance diode of the AM and FM antenna tuning circuits, the power of the antenna tuning circuit and the tuning circuit inside the receiver is This has the advantage that it is possible to easily obtain a ranking, and it is possible to prevent interference from signals other than the desired signal, and to prevent deterioration of signal-to-noise characteristics. It's still AM.

Since the FM antenna tuning circuit and the receiver can be connected by a single coaxial feed line as before, the overall configuration can be significantly simplified, which is extremely advantageous in practical use.

[Brief explanation of drawings]

FIG. 1 shows an AM including the antenna tuning circuit of the present invention. A block diagram of an embodiment of an FM radio receiver,
FIG. 2 is a specific electrical wiring diagram of one embodiment of the antenna tuning circuit of the present invention. 1... Antenna, 3, 10... Duplexer, 4... FM antenna tuning circuit, 5... AM
Antenna tuning circuit, 6...Mixer, 8...
Coaxial feeder line, 11...FM radio receiver, 12...
...AM radio receiver, 8.16 ... Capacitor, 9.17 ... Inductance, 1o
, 13...AM and F M varactors,
26... Tuning control voltage generator.

Claims (4)

[Claims] (1) Connected to an antenna for both AM and FM,
A capacitor with frequency characteristics that allows the passage of signals but substantially blocks AM signals, and an inductor with frequency characteristics that allows passage of AM signals but substantially blocks FM signals. The FM signal and AM signal split by the splitter are respectively input, and the capacitance value changes depending on the tuning control voltage.
FM and AM antenna tuning circuits in which the antenna tuning frequency changes, and the output signals of these antenna tuning circuits are mixed with each other using a J variable capacitance diode. , and a mixer for supplying the AM radio receiver to the AM radio receiver. (2) AM is the tuning control voltage to the variable capacitance diode that constitutes each AM and FM antenna tuning circuit. An antenna tuning circuit for a vehicle-mounted AM or FM radio receiver according to claim 1, wherein the antenna tuning circuit is configured to supply the voltage from a tuning control voltage generator provided on the FM radio receiver side through a coaxial feed line. (3) Set the tuning control voltage from the tuning control voltage generator to AM,
An antenna tuning circuit for a vehicle-mounted AM or FM radio receiver according to claim 2, which is configured to apply a common voltage to all tuning variable capacitance diodes constituting the FM radio receiver. (4) A duplexer and antenna tuning circuit close to the antenna for both AM and FM.