Sensing full-band high-sensitivity radio

Shunluo high frequency inductor, parallel stack inductor, shun winding inductor, authorized agent

This machine adopts self-made variable inductor (also known as PVL) to select the platform. Compared with the volume-adjusting radio, it has the following advantages: (1) high sensitivity; (2) good selectivity; (3) good shock resistance; )strong and sturdy.

The band of this machine is shown in Table 1, and the squelch sensitivity is shown in Table 2.

The variable capacitor has been rotated for half a turn, so the short wave is generally divided into 9 to 12 bands, and the distance between the table and the table is sufficient. The variable inductor has to be rotated 4 and a half to complete a stroke, and the short wave is divided into 5 bands. The distance between the station and the table is sufficient. The band is divided too much, and the distance between the table and the table is too wide. Instead, I feel uncomfortable and uncomfortable.

The radio's radio effect is mainly not reflected in the sound effect, but in how much it is received. Especially in remote areas, the number of stations is determined by the sensitivity of the squelch. If the squelch sensitivity is in decibels (dB), the smaller the number of dBs tested, the higher the squelch sensitivity and the better the radio gain. As can be seen from Table 2, the noise sensitivity of the FM and short-wave (SW) bands of this unit is quite high. The medium wave performance of this machine is general, because the casing used for testing this machine is not big enough, and the medium wave magnetic rod used is small and short. If the case is large enough to fit a long, thick magnetic bar, the squelch sensitivity can be as low as 76dB or less.

Fundamental

As we all know, the inherent oscillation frequency fo of the tuning loop composed of the inductor L and the capacitor C is determined by:

Fo=1/2Ï€LC

It can be seen that the natural frequency fo of the loop can be changed regardless of whether L or C is changed. When the natural frequency is the same as the carrier frequency in the information of a certain station input by the antenna, a series resonance is generated, and the station can be received.

The tuning loop consisting of L and C also has a very important parameter called the quality coefficient, also called Q value. The calculation formula of Q value is:

Q=2Ï€5L/R or Q=1/2Ï€5CR

Where R is the resistance value of the loop. If the R of the two loops are the same, the Q value is higher at L or C hours. When the Q value is high, the sensitivity is high, and the selection is good, and the receiving effect is good.

The top left picture is in the radio: PVC tuning loop, and the bottom left is the tuning loop of the PVL.

Taking the FM band as an example, the Ll of the radio is generally a 3.5~4.5T air-core coil. The L2 of this tuned radio is also an air-core coil of 3.5 to 4.5T, but a small magnetic core that can be moved is inserted into the coil, so L2 is much larger than L1. The Q value of FIG. 2 is higher than the Q value of FIG. Obviously, for the tuning and tuning radio, if the ICs used are the same, the design and adjustment of the radio circuit are in the best state, the sensitivity of the tuning radio is definitely higher than the sensitivity of the radio, and the receiving effect is good.

PWL structure

The figure is a schematic diagram of the structure of the PVL. In the figure, L is a coil winding, a small magnetic core a is inserted therein, a small copper screw rod b is set on the top of the small magnetic core, and a small copper screw rod is screwed into the corresponding hole of the moving piece c. There is a groove at the top of the small copper screw rod. As shown in Figure 3(b), insert the screwdriver into the groove and turn the screwdriver to rotate the small core to the appropriate position. The moving piece is embedded with a screw nut. When the screw rod d of the PVL is rotated, the moving piece moves, so that the small magnetic cores move synchronously, thereby synchronously changing the inductance of each winding.

It is worth mentioning that the screw pattern of the PVL screw rod is different from the single-head screw pattern of the general screw, and is a 4-head screw pattern. That is, the screw pattern is generally composed of four independent screw patterns, and the sectional view of the screw and the nut is as shown in Fig. 3(c). This screw pattern allows the screw to control the nut in four places. Therefore, when the nut is moved by the rotary screw, the movement of the moving piece can be efficiently and smoothly driven to avoid shaking due to the gap existing between the screw and the nut. And when the moving piece stays at a certain position, the moving piece can be effectively stabilized at the position, so that the small magnetic core is effectively stabilized in the position in the winding. Experiments have shown that when a station is received, the PVL is not hit with a hard object, which ensures the stability of the frequency from the stability of the mechanical structure.

circuit analysis

The circuit diagram of this unit is shown on the previous page. The triode's VT2 and VT3 form an electronic switch that replaces the general FM/AM switch. It can be seen from the figure that except for the local oscillator, the high-amplifier, and the input circuit, the rest is the same as the PVC radio circuit of the same IC, and these parts will not be described again. The PVL of this machine is self-made. It has 6 windings, and the functions of each winding are:

1 FM local oscillator winding: PL4

FM high-level winding 1: PL3

SW local oscillator winding 1: PL6

One MW local oscillator winding: PL5

MW, SW common high-level winding 2 PL1 and PL2

When designing and adjusting the tuned radio circuit, it may be uncomfortable to compare it with the tuned radio circuit, but it must be remembered: the status and role of L and C in the tuning loop involving frequency coverage and high-level tuning. Just swapped. Now with FM instructions, let's take another look.

Figures 5 and 6 are tuning loops for PVC and PVL, respectively. It can be seen that C9 corresponds to L1, PL4 corresponds to C3, and L8 corresponds to C1 and C2. In the adjustment, the adjustment methods of Figure 6 and Figure 5 are just the opposite:

Low end: L1 in the upper left picture, C9 in the lower left picture; C9 in the lower left picture; C2 in the upper left picture, L8 in the lower left picture; Medium wave adjustment: PL5, T3 and C10 form the local oscillator tuning loop, in the case of correctly selecting the C10 value, the lowest The point frequency can be achieved by adjusting the small core of PL5, and the highest point frequency can be adjusted by T3. The high-level tuning loop consists of PL1 and PL2 and C7. The overall adjustment method is: in the case of correctly selecting the C7 value, the low-end adjustment of the small magnetic core of PL2, the high-end adjustment of the small magnetic core of PL1.

Short-wave adjustment: After adjusting the medium wave, adjust the short-wave again. As can be seen from FIG. 4 and Table 1, SW2, SW3, SW4, and SW5 change the frequency by changing the inductance of the variable inductor winding PL6 to receive different stations. The short-wavelength band is divided by the different inductances and capacitors of the band switch S-4 at both ends of the PL6. The composition of the corresponding short-waveband local oscillator tuning loop is as follows:

Since the frequency of SW1 is low, the local oscillator tuning loop of the SW1 band must be composed of the medium-wave local oscillator variable inductor windings PL5 and C11.

Short-band frequency range adjustment

The lowest frequency point of the entire short wave is also the lowest frequency point of the SW1 band, which can be achieved by adjusting the value of C11.

The shortest frequency point of short-wave using PL6 is also the lowest frequency point of SW2. When the C12 value is correctly selected, the small core position of PL6 can be obtained to obtain the lowest frequency point of SW2, and the highest frequency of the whole short-wavelength. The point is also the highest frequency point of SW5. When the value of C15 is correctly selected, the fine-tuning inductor L11 can reach this highest frequency point.

On the right side of the previous page, there are a series of values ​​of inductance and capacitance. Using these values, the bands shown in Table 1 can be obtained.

Short-range high-level tuning

The signal input by the antenna is amplified by the triode VT1 and then input into the IC. Nowadays, many so-called multi-band short-wave radios are available on the market. In order to save cost, all short-wavelength bands use the same resistor or inductor as the VT1 load, resulting in high noise and noise sensitivity. not tall. The goal of this machine is to optimize the squelch sensitivity of each short-wavelength. Therefore, VT1 selects different loads for different short-wavelengths through switch S-2. The optimal value of each band as the inductance and capacitance of the load is related to the distributed inductance and distributed capacitance of the specific circuit board. It should be determined experimentally to achieve The best squelch sensitivity. The values ​​on the right side of Figure 4 are for reference and the best values ​​are determined experimentally.

Input circuit

The modern living environment is inseparable from various electrical appliances. The interference waves emitted by the industry and these electrical appliances are becoming more and more serious. The frequencies of these interfering radio waves are mostly concentrated in the middle wave frequency band. In some places, the interference is serious and the medium wave radio station cannot be effectively received. Experiments have shown that if the medium wave signal is introduced by the whip antenna, the interference is more serious. When the magnetic wave rod and its coil are used to introduce the medium wave signal, the interference is not as serious as the rod antenna. The purpose of the switch S-1 is to ensure that the medium wave signal is input by the magnetic bar coil in the medium wave state, the magnetic bar of the machine and The coil is only used for absorbing medium wave waves and does not have a tuning effect. PL1, PL2, and C7, which are VT1 loads, function as tuning. Experiments have shown that the magnetic rod coil L1 is not the more the number of turns, the better, in a certain number of turns, it will reduce the interference without reducing the sensitivity, the number of turns of L1 is determined by experiments.