JPS6234292B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention automatically tunes the receive frequency to the transmit frequency in an SSB mode transceiver.
This is related to AFC equipment, and its purpose is to enable good AFC to be applied.

Normally, when considering mutual communication between wireless stations in an SSB transceiver, the allowable frequency deviation between each other is extremely important. must match exactly.

Figure 1 shows the frequency spectrum arrangement of an SSB transmission signal using a reduced carrier wave as a pilot signal, and Figure 2 shows a general reception method in which AFC is applied by extracting the pilot signal and comparing the phase with an internal reference signal. The block diagram of the section is shown below.

In FIG. 1, A is the SSB band, B is the audio band, and C is the pilot signal.

In FIG. 2, an incoming signal is amplified by an RF amplifier 1, and is added to a mixer 2 together with the output of a first local oscillator 12 composed of a VCO (voltage controlled oscillator), where it is converted into an intermediate frequency signal. This signal is applied to a demodulator 5 through a crystal filter 3 and an IF amplifier 4. The demodulator 5 demodulates the audio signal using the signal from the carrier oscillator 7 and the intermediate frequency signal, and the audio signal is amplified by the amplifier 6 and sent to the speaker S.
It is added to the sound and is emitted aloud.

Further, the pilot signal is extracted by a bandpass filter 8 at the IF stage, amplified by a pilot signal amplifier 9, and then input to a phase comparator 10. This phase comparator 10 compares the phases of the pilot signal and the reference frequency output from the carrier oscillator 7, and inputs the output through the low-pass filter 11 to the VCO of the first local oscillator 12, thereby automatically matching the transmitting and receiving frequencies. let

In order to increase the frequency accuracy during AFC lock in such a receiving section, the band of the bandpass filter 8 for extracting the pilot signal should be made as narrow as possible in order to ensure the S/N ratio of the pilot signal input to the phase comparator 10. It needs to be narrowband. However, considering the AFC lock range and lock-in speed, it is better for the bandpass filter 8 to have as wide a bandwidth as possible, and requires characteristics opposite to those of the bandpass filter from the viewpoint of frequency accuracy.

The present invention is intended to eliminate such contradictory points required for the bandpass filter 8. FIG. 3 shows an example of the configuration of a receiving section according to an embodiment of the present invention. In this figure, parts corresponding to those in FIG. 2 are designated by the same reference numerals. Reference numeral 13 denotes a PLL/AFC system lock determination circuit, which outputs an output signal 0 in the unlocked state and outputs an output signal 1 in the locked state. 14 is a bandpass filter of variable band type controlled by the output signal of the circuit 13, and the bandwidth when the output signal of the circuit 13 is 0 is shown in FIG.
Take it wide as shown. Further, the bandwidth of the output signal 1 of the circuit 13 is switched to a narrow band characteristic as shown as E in FIG. 4B.

With this configuration, the bandpass filter 14 has a broadband characteristic in the unlocked state, and although the S/N of the pilot signal is affected by the audio signal and deteriorates somewhat, the lock-in speed becomes faster and the lock range becomes wider. . Further, after the AFC is locked, the bandpass filter 14 is switched to a narrow band, so that the S/N of the pilot signal is improved and the accuracy of frequency tracking is increased.

As described above, according to the present invention, the drawbacks associated with conventional AFC circuits are solved by setting the bandpass filters for extracting pilot signals to optimal bandwidths when unlocking and locking AFC, respectively, thereby improving its practical use. Value can be significantly increased.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the frequency spectrum of an SSB transmission signal, FIG. 2 is a block diagram of a general SSB receiving section, and FIG. 3 is a block diagram of an SSB receiving section including an AFC device in an embodiment of the present invention. FIG. 4 is a diagram showing the spectrum of the signal. 13...PLL/AFC system lock judgment circuit, 14
...Bandpass filter.

Claims (1)

[Claims] 1 A variable band bandpass filter that extracts the pilot signal component included in the SSB transmission signal;
A PLL that compares the extracted pilot signal with the reference frequency and adjusts the intermediate frequency signal to a predetermined frequency.
It has an AFC circuit and a determination circuit that determines whether the PLL/AFC circuit is locked or unlocked, and when the determination circuit detects the unlocked state, it switches the bandpass filter to a wide band.
An AFC device characterized in that when the determination circuit detects a lock state, the bandpass filter is switched to a narrow band.