JPS6016717A - Afc device - Google Patents

Abstract

PURPOSE:To quicken the lock-in speed and to widen the lock range by setting a band pass filter for extracting pilot signal to an optimum band width respectively at unlocking and locking of AFC. CONSTITUTION:A lock discriminating circuit 13 of a PLL-AFC system outputs an output signal 0 at unlock state and outputs an output signal 1 at lock state. The bandwidth of a band pass filter 14 is switched to a broad band characteristic when the output signal of the circuit 13 is 0 and to a narrow band characteristic when the output signal is 1. Thus, the band pass filter 14 has the broad band pass characteristic at the unlock state and the S/N of a pilot signal is deteriorated more or less by the effect of a sound signal, but the lock-in speed is quickened and the lock range becomes wider. Since the band is switched to the narrow band after lock, the S/N of the pilot signal is improved and the accuracy for tracking frequency is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AFC device that automatically tunes the receiving frequency to the transmitting frequency in an SSB mode transceiver, and its aim is to ensure that good AFC is applied.

Normally, when considering the same amount of wireless mutual communication in a 5SB) transceiver, the mutual frequency deviation tolerance is extremely important. By applying AFC using a manual tally fire or pilot signal, the transmission frequency It is necessary to exactly match the receiving frequency.

Figure 1 shows an SS using a reduced carrier wave as a pilot signal.
FIG. 2 shows a block diagram of a general receiving section that extracts the pilot signal and performs AFC by comparing the phase with an internal reference signal.

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

In FIG. 2, the incoming signal can be amplified by the RF amplifier 1, and V
The first local oscillator 1 consists of a CO (voltage controlled oscillator).
2 is applied to mixer 2 and converted into an intermediate frequency signal. This signal is connected to crystal filter 3 and IF
It passes through an amplifier 4 and is applied to a demodulator 5. This demodulator 6
Then, the audio signal is demodulated by the signal from the carrier oscillator 7 and the intermediate frequency signal, amplified by the amplifier 6, added to the spill force S, and emitted.

In addition, the pilot signal is passed through a bandpass filter 8 at the IF stage.
The phase comparator 10 is extracted by the pilot signal amplifier 9, amplified by the pilot signal amplifier 9, and then inputted to the phase comparator 10.
Now, compare the phases of the pilot signal and the reference frequency output from the carrier oscillator B, and pass the output to the low-pass filter 1.
1 to the VCO of the local oscillator 12, the transmitting and receiving frequencies are automatically matched.

In order to increase the frequency accuracy at the time of AFC lock in such a receiving section, in order to ensure the S/N of the pilot signal input to the phase comparator 10, the band of the bandpass filter 8 for extracting the pilot signal should be increased as much as possible. 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, which requires characteristics opposite to those of the bandpass filter from the viewpoint of frequency accuracy.

The present invention is intended to eliminate such contradictions 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. 13
is a PLL-AFC system lock determination circuit, which outputs an output signal 0 in an unlocked state and outputs an output signal 1 in a locked state. Reference numeral 14 denotes a band-pass filter of variable band type controlled by the output signal of the circuit 13, and when the output signal of the circuit 13 is O, the bandwidth is wide as shown as D in FIG. 4A. Furthermore, the bandwidth of the output signal 10 of the circuit 13 is not shown as E in the opening of FIG. 4, and is switched to a narrow band characteristic.

With this configuration, in the unlocked state, the bandpass filter 14 has wideband pass characteristics, and although it deteriorates somewhat due to the influence of the S/Nid of the pilot signal and the audio signal, the lock-in speed is fast and the lock range is wide. Become. Also, after the AFC is locked, the bandpass filter 14
Since the signal is switched to a narrow band, the S/N ratio of the pilot signal is improved and frequency tracking accuracy 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 the AFC, thereby improving its practical use. can significantly increase its value.

[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 4
...Bant pass filter.

Claims (1)

[Claims] An AFC device comprising: a variable band filter for extracting a pilot signal component included in an SSB transmission signal; and switching means for switching the bandwidth of the filter using an AFC unlock signal and a lock signal.