JPS5847895B2 - radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio receiver that can accurately and stably read reception frequencies, and particularly to a radio receiver that can display reception frequencies numerically using a frequency counter.

In general, shortwave broadcasting uses an extremely wide frequency band with a carrier wave frequency of 3 MHz to 30 MHz, and the number of broadcasting stations within this band is said to be 4000 to 5000 stations.

Moreover, the minimum unit of the carrier frequency is assigned to the KHz unit.

Therefore, shortwave receivers are required to read the reception frequency accurately and stably.

Conventionally, one of the best means to obtain the display accuracy of the received frequency in a superheterodyne radio receiver is to directly count the oscillation frequency of the local oscillator and calculate the sum or difference of the intermediate frequency (for example, 455 KHz). Some devices display the received frequency numerically after correction.

However, the above 455KHz correction is 100KHz, 10KHz, IK on the numerical display.
Three digits of Hz must be corrected individually, making the structure for the frequency counting function very complex and expensive.

The present invention overcomes the above-mentioned drawbacks and provides a radio receiver that displays accurate reception frequencies with a simple structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The radio receiver of the present invention will be described below with reference to drawings of embodiments.

In the figure, 1 is an external frequency input terminal, 2 is a high frequency amplifier, 3 is a first local oscillator having a variable frequency oscillator 7,
4 is the first mixer, 5 is the output terminal of the first local oscillator 3, 8
is the first intermediate frequency amplifier, 9 is the second mixer, 10 is the second local oscillator, 11 is the second intermediate frequency amplifier, 12 is the output signal terminal of the second intermediate frequency amplifier 11, and 13 is the output of the variable frequency oscillator 7. 14 is a gate circuit, 15 is a frequency counter section, 16 is a band frequency correction setting device, and 17 is a numeric display.

Desired received signal (received frequency f.

) is applied to the external high frequency input terminal 1, and after being amplified by the high frequency amplifier 2 if necessary, is applied to the first mixer 4.

The high frequency amplifier 2 normally receives the above reception frequency f.

It is preferable to have a tuning circuit whose center frequency is .

On the other hand, the output signal of the first local oscillator 3 (its frequency f1) is . The signal is applied to the first mixer 4 through the local oscillation output terminal 5, and the first intermediate frequency f2 of f1-fo (or f1+fo) is obtained at its output.

Further, this intermediate frequency signal is amplified by a first intermediate frequency amplifier 8 and then applied to a second mixer 9.

At the same time, the output signal of the second local oscillator 10 is also applied to the second mixer 9, so that a second intermediate frequency signal is obtained at its output terminal, which is amplified by the second intermediate frequency amplifier 11.

The circuit structure described above or the double superheterodyne reception system is widely used in this type of radio receiver.

That is, the second intermediate frequency output signal terminal 12 receives an intermediate frequency signal after frequency conversion so that the desired received signal is sufficiently selected and amplified.

Here, the first intermediate frequency f2 is set to a frequency whose lower digit is 0.

That is, for example, when f2 is set to 22, 0 0 0 MHz, the oscillation frequency f1 of the variable frequency branch oscillator 7 is set to 7,
7 4 5 MHz is f.

-5, 7 4 5 MHz can be received. In this way, if the lower digit of the first intermediate frequency f2 is set to O, the reception frequency f is obtained.

The lower digits 7, 4, and 5 of the oscillation frequency f1 match.

Therefore, when the oscillation frequency f0 is counted by the frequency counter section 15, the reception frequency is the upper digit (MHz digit)
The only difference is

Therefore, the first intermediate frequency f2(-2,OOOM
Hz) is applied as a correction value from the band frequency corrector 16 to the frequency counter section 15, and only the MHz digit is corrected (
(Here, subtraction) to obtain the accurate reception frequency f.

It is town Noh to display numbers.

Conventionally, this required correction in the frequency counter section down to the lower digits, but according to the present invention,
Since only the upper digits need to be corrected, the circuit structure can be greatly simplified.

Although the embodiments described above are based on a double super reception system, it goes without saying that it is also possible to implement a single super reception system or a triple super reception system.

In a multi-conversion receiving power type with double super or more, the present invention can be used to realize a radio receiver with even better operability.

That is, the second local oscillator 10 is configured as an oscillator whose frequency can be varied within a relatively narrow range, so that fine adjustment of the range of the second intermediate frequency amplifier 11 can be made.

By using this fine adjustment function and slightly shifting the second local oscillation frequency with respect to the reception frequency, it is possible to generate a beat based on the difference frequency and demodulate telecommunications.

At this time, it has no relation to the reception frequency display function,
Therefore, there is no need to provide an independent beat oscillator, which was conventionally used for demodulating telecommunications, and the circuit becomes simple and inexpensive.

In addition, using the above fine adjustment function, the first
, it is also possible to correct variations in the second intermediate frequency and frequency shifts (drift) due to temperature changes, and this is very convenient in operation because it does not affect the displayed frequency in any way.

As described above, according to the present invention, the local oscillation frequency f1 and the reception frequency f.

By making the lower digits match, if the local oscillation frequency f1 is counted and only the upper digits are corrected using the intermediate frequency value, the received frequency can be displayed correctly in numbers, so the above correction structure is This greatly simplifies the process and allows a radio receiver that can display the correct frequency to be constructed at low cost.

[Brief explanation of the drawing]

The drawing is a block diagram showing an embodiment of the radio receiver of the present invention. 3...Local oscillator, 4...Mixer, 7
... Frequency variable oscillator, 14... Gate circuit, 15... Frequency counter section, 16...
...Frequency correction setting device, 18...Numeric display.

Claims (1)

[Claims] 1. Reception frequency f. It has a mixer which applies a received signal with a frequency f1 and an output signal of a local oscillator with a frequency f1 and converts the frequency to an intermediate frequency f2 (f1-fo or f1+f) to obtain an intermediate frequency signal,
The local oscillator is a frequency variable oscillator, and a frequency counter that counts the oscillation frequency f1 of the frequency variable oscillator and can correct the count value of the oscillation frequency f1 by addition or subtraction, and displays the output of the frequency counter numerically. and a numeric display indicating the reception frequency f. and the oscillation frequency f1 of the frequency variable oscillator, and the lower digits thereof are made to match, and the oscillation frequency f and the value of the intermediate frequency f2 as a correction value are input into the frequency counter to obtain the reception frequency f. A radio receiver characterized by displaying numbers.