JPH054352Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to an antenna input circuit suitable for application to a dual tuner type cassette tape recorder and the like.

[Prior Art] A dual tuner type cassette tape recorder is constructed so that each tuner can be used independently.

And when one channel is AM/FM channel, the other channel is
AM/FM/VHF/UHF tuners are often installed.

In such a dual tuner type, the antennas used for each tuner are usually provided independently. That is, loop antennas, for example, are independently provided at predetermined positions within the housing of the cassette tape recorder, and signals obtained from each loop antenna are fed to the respective antenna input circuits.

However, attaching antennas according to the number of built-in tuners in this manner increases costs and is a bottleneck in downsizing the device.

In addition, it was necessary to devise an installation plan to avoid mutual interference.

The above-mentioned drawbacks can be overcome by using a single common antenna.

To do so, for example, a configuration as shown in FIG. 2 may be used. That is, the antenna feed terminals 3A and 3B are connected to the first and second tuners 1 and 2.
For example, a single loop antenna 4 functioning as an internal antenna may be connected to this common antenna.

[Problems to be solved by the invention] By the way, if the antennas are made to have a common configuration as described above, the following problems arise.

For example, assume that the first tuner 1 receives station A in FIG. 3, and the second tuner 2 receives station B.

The first tuner 1 which is receiving station A is impedance matched to have an impedance of 75Ω. However, for the frequency bands of other broadcasting stations, the impedance is low as shown by curve _L1 in FIG.

Similarly, the second tuner 2 that is receiving station B
The impedance is matched to 75Ω, but the impedance is low for the frequency bands of other broadcasting stations, as shown by curve _L2 in the figure.

Therefore, the presence of the second tuner 2 causes interference such that the reception level of the A station being received by the first tuner 1 is divided. As a result, the reception level to the first tuner 1 is significantly attenuated. The same can be said of the second tuner 2.

If the antennas are shared in this way, there are drawbacks such as mutual interference and decreased sensitivity.

Therefore, this invention solves these conventional problems and proposes an antenna input circuit that prevents mutual interference and deterioration of sensitivity even when an antenna is shared.

[Technical means for solving the problem] In order to solve the above problem, in this invention, the signal fed from the antenna is supplied to a broadband low-noise amplifier via a coupling transformer, and its output is 1st for matching
and a second resistor to be supplied to the tuning circuits of the first and second tuners.

[Operation] In this configuration, since input signals are fed to each of the tuners 1 and 2 via the wideband amplifier 20, the impedance seen from the tuners 1 and 2 side is very low.

Therefore, the impedance of the input signal supplied to the second tuner 2 with respect to the first tuner 1 is reduced to a negligible level. As a result, the second
The input signal to the first tuner 2 will not interfere with the first tuner 1 and have an adverse effect.

Further, since the signal amplified over a wide band by the amplifier 20 is supplied to the tuners 1 and 2, the reception level does not decrease. In other words, the input sensitivity does not deteriorate.

[Embodiment] Next, a case in which an example of the antenna input circuit according to the invention is applied to the above-mentioned dual tuner type cassette tape recorder will be described in detail with reference to FIG. 1 and subsequent figures.

FIG. 1 shows an antenna input circuit 10 according to this invention.
In this system diagram showing an example, a single loop antenna 4 functioning as an internal antenna provided within the casing of a cassette tape recorder is connected to a common power supply terminal 3A, 3B.

The input signals fed to the terminals 3A and 3B are fed through a coupling transformer 11 to a broadband and low noise amplifier 20.

The broadband low noise amplifier 20 is a juncture.
FET 21 is used as the amplification element, and is connected in a source follower type, and the input signal is output from the source.

This input signal is connected to a DC cut capacitor 12,
13 and the tuners 1 and 2 via the first and second resistors 14 and 15 for impedance matching.
distributed to. Specifically, each tuning circuit 3
0 and 31 at the same time.

In this example, AM/
FM Chiyuna is AM/FM/ as Chiyuna 2.
VHF/UHF tuner is used.

Here, since the FET 21 is configured as a source-grounded type, the impedance of the broadband amplifier 20 seen from the tuner 1 and 2 sides is the same as that of the resistors 14 and 15.
It is so low that it can be considered 0 compared to .

Therefore, signals other than input signals from the receiving broadcast station are almost completely bypassed via the resistor 22. In other words, the wideband amplifier 20 functions as a buffer amplifier with wideband and low noise characteristics.

Therefore, the first tuner receives station A, and the second
When the tuner is receiving station B,
Since the reception level of the station is not divided by the second tuner, there is no attenuation. Similarly, since the receiving level of the B station is not divided by the first tuner, the receiving level of the B station is not attenuated.

This prevents mutual interference and prevents the S/N of the input signal from deteriorating.

Further, since the input signal is wideband amplified by the amplifier 20 and then guided to the respective tuning circuits 30 and 31, the sensitivity of the input signal does not deteriorate.

Note that although a loop antenna is used as the internal antenna 4 described above, other antennas may also be used.

The pair of tuners 1 and 2 used as a dual tuner is also just one example.

The above description deals with the case where there are two tuners, but even when two or more tuners are connected, the impedance of the broadband amplifier 20 as seen from each tuner is determined by the impedance matching resistor of each tuner. Since it is so low that it can be considered as 0 compared to , there is no mutual interference between the tuners or a decrease in sensitivity.

[Effects of the invention] As explained above, in this invention, an amplifier with wideband low noise characteristics is used, and the input signal from the antenna is fed to each tuner via this amplifier.

According to this configuration, the antenna can be shared, which reduces costs. In addition, when using a pair of antennas, the installation positions of each antenna must be carefully considered to prevent mutual interference. The invention also eliminates the need for such design efforts.

Furthermore, even if antennas are shared, problems such as mutual interference and decreased sensitivity can be easily resolved.

Therefore, this invention is extremely suitable for application to antenna input circuits in cassette tape recorders and other receivers that employ the dual tuner type described above.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an example of an antenna input circuit according to this invention, FIG. 2 is a system diagram for explaining this invention, and FIG. 3 is a characteristic diagram for explaining its operation. 1, 2... Chuyuna, 4... Antenna, 3A,
3B...Power supply terminal, 10...Antenna input circuit,
14, 15...Resistor for impedance matching, 20...Broadband low noise amplifier.

Claims (1)

[Scope of utility model registration request] In the antenna input circuit of a tuner in which a single antenna is shared by multiple tuners, the signal fed from the antenna is passed through a coupling transformer to a broadband buffer with low noise characteristics made of an amplifying element such as a junction FET. An antenna input circuit characterized in that the antenna input circuit is supplied to an amplifier (buffer amplifier), and the output thereof is supplied to a tuning circuit of each tuner via an impedance matching resistor.