JPS6029249Y2 - Improvement of variable bandwidth intermediate frequency amplifier circuit - Google Patents

Description

[Detailed explanation of the invention] This invention was originally filed by the same applicant in 1973.
'N, No. 100091 and Utility Model Application No. 28318 of the Showa 5 Group.

In the front, as shown in FIG. 1, bandpass filters having substantially the same bandwidth are used at least for one of the illustrated first intermediate frequency amplification stage 1 and third intermediate frequency amplification stage 3, and for the second intermediate frequency amplification stage 2, The local oscillation frequencies of the first frequency conversion stage 4 and the second frequency conversion stage 5 are supplied from a single local oscillator 6, and by changing the oscillation frequency, the relative bandwidths of the first and second filters can be adjusted. By changing the overlap of targets, the total passband width could be changed continuously.

The state of change in the total passband width with respect to the change in the local oscillation frequency at this time is illustrated in Figure 2, and A
is a state in which the center frequencies of the first and second filters match, the passband width is the widest, and the relative positions of the sidebands of LSB and IJSB with respect to the BFO frequency during SS reception are almost similar. be.

B is a case where the local oscillation frequency is moved to a lower side, for example, and the passband width is narrowed, and the demodulation of I and SB produces a sound with the high sidebands cut off.

Furthermore, in the same band condition, demodulating USB produces a sound like C, with the low sideband cut off.

When used for the purpose of eliminating interference, there is no problem because the bandwidth is normally used in the widest state A, and the variable bandwidth adjustment is only activated in the case of interference, but if you prefer high-cut or low-cut LS when used in conjunction with received sound
It is desirable that the received sound quality does not change when switching between B and USB.

In this invention, the frequency change of the local oscillator for varying the bandwidth by the above method is controlled by voltage, and the polarity of the voltage applied across the voltage controlled variable resistor is determined by the mode.
It is configured to be inverted in common with the LSB-USB switching of the switch, and an example of the circuit of that part is shown in FIG.

Variable frequency crystal oscillator circuits with good frequency stability are often used as local oscillators.

In the circuit, 10 is an active element, 11 is a crystal oscillator, and 12 is a voltage variable capacitance diode connected in series with this, the capacitance of which is changed by a control voltage from a variable resistor 13 to control the oscillation frequency.

The amount of change in control voltage required for this is the series resistance of 14.15
Set by.

The mode switch ■ switches the operation of the BFO of LSB and USB and also inverts the polarity of the variable resistor.
If it is not possible to use a common switch circuit due to circuit limitations, another switch circuit may be used for mechanically interlocking the switches.

The state of bandwidth variable in the circuit of this invention and L in ssm
The relationship between SB@USB and the sideband is shown in Figure 4.

In A, the center frequencies of the first and second filters match and the total bandwidth is the widest, which is almost the same result as A in Figure 2, but in B, a variable resistor for adjusting the bandwidth is used. This is a case where it is adjusted to be high cut when receiving LSB, and C
is the case when the mode switch is switched to the USB reception state without adjusting the variable resistor, and although the center frequency of the passband changes, the relative position with respect to each BFO frequency is almost the same. The demodulated sound quality is also almost the same.

As described above, this invention has an even greater practical effect by compensating for the difference in demodulated sound quality between LSB and USB when the bandwidth was changed in the previous application.

[Brief explanation of drawings]

Figure 1 is a block diagram of the intermediate frequency variable bandwidth circuit, Figure 2 is a diagram of the relationship between the variable band and LSB/USB in the circuit shown in Figure 1,
FIG. 3 shows an example of a circuit to which the present invention is applied, and FIG. 4 shows a relationship diagram between the variable band and LSB-USB in the circuit of the present invention. 1...First intermediate frequency amplification stage, 2...Second intermediate frequency amplification stage, 3...Third intermediate frequency amplification stage, 4...Third intermediate frequency amplification stage 1 frequency conversion stage 5... second frequency conversion stage, 6... local oscillator, 7...
...Product detection, 8...BFo, 10.
...Active element, 11...Crystal oscillator, 1
2... Voltage variable capacitance diode, 13...
...Variable resistor 14.15...Resistor, 16
······switch.

Claims (1)

[Scope of utility model registration request] There are at least three types of intermediate frequency amplification stages and a frequency conversion stage between the stages, the first intermediate frequency amplification stage and the third intermediate frequency amplification stage have the same center frequency, and at least the first intermediate frequency amplifier and the third intermediate frequency amplification stage have the same center frequency. One of the three intermediate frequency amplifiers and the second intermediate frequency amplifier are provided with bandpass filters having substantially equal bandwidths, and the local oscillation frequencies of the first frequency conversion stage and the second frequency conversion stage are supplied from a single local oscillator, The oscillation frequency of this local oscillator is configured to be able to change in frequency approximately equal to the bandwidth of the bandpass filter, and the frequency change of the local oscillator is caused by voltage control, and is controlled by the voltage control variable resistor. An intermediate frequency amplifier circuit for a radio receiver or the like, characterized in that the polarity of a voltage applied to both ends is inverted in common or in conjunction with LSB-USB switching of a mode switch.