Production of power standing wave table

Photocoupler

The power standing wave meter is one of the necessary instruments for the majority of HAM, and it can be made in addition to the products of regular manufacturers. According to the method described below, the standing wave table of DIY is also very effective. As for the measurement of the homemade power and the standing wave ratio, for amateurs, it is only a relative value, and it is not necessary to care about it. The power value is within the allowable error, and the standing wave ratio SWR can read 1.5, 2, and 3. In the trial production process, the author feels that the production of the standing wave ratio table is "it is difficult to embroider flowers." Although there are only a few components, it is not easy to adjust the pointer of the REF file to zero. Only by understanding its principles can debugging be carried out smoothly. After your personal DIY, I believe that you will have a new understanding of the standing wave watch.

One: Power standing wave ratio table principle of magnetic loop mutual inductance method

(Figure) First analyze its high frequency circuit. Draw it as an equivalent circuit for analysis. Let the forward voltage be U input and the reverse voltage be U reverse. At two points a and b, why can we get independent U-in and U-reverse voltages? If the voltages of U-in and U-inversion cannot be separated separately, it is impossible to test positive and reverse waves. First, the U input and U reverse voltages are taken out from the transmission line L1. When a high-frequency current is passed through L1, an induced electromotive force is necessarily generated on the secondary coil L2 of the high-frequency transformer T.

e=jωMI

This electromotive force e forms a high-frequency current i in the high-frequency transformer T and R1, R2. The magnitude of the current in the loop is completely dependent on the inductive reactance L of T.

R=R1+R2

The following relationship is found at each point on the transmission line L1:

U=U in+U inversion I=I in-I inversion————(1)

The impedance at each point on the transmission line is the same.

Therefore, the current in the network is at the resistance R1 = R2; the capacitors C1 and C2 form a voltage divider, and K is the voltage division ratio. The voltage divided on C2 is U3.

U3=KU=K (U in +U reverse)——————(4)

Because the partial pressure ratio of C3 and C4 is equal to the partial pressure ratio of C1 and C2:

U4=K (U in +U reverse)

Now set: U3=U3/2, U4=U4/2.

The partial pressure ratio K is set to be equal to MR/LZc, and U1 and U3, U2 and U4 are added respectively. Since U1 is detected, 1/2 U1 is obtained at point a, and the same U2 is obtained at point b. 2U2.

Then the voltage at point a is: 1/2U1 + 1/2U3 = 1/2U into - 1/2U reverse + 1/2U into + 1/2U reverse = U into

The voltage at point b is: -1/2U2+1/2U4=-1/2U into +1/2U inverse +1/2U into +1/2U anti=U anti

Fig. 3 is a schematic diagram of a power standing wave table circuit fabricated by a magnetic ring mutual inductance method by resistance division. First, the electrical schematic is analyzed. Its high frequency loop is equivalent to Figure 4. As seen from Fig. 4, R1 = R2, so U1 = U2 is known from equation (3);

Resistors R3 and R4 form a voltage division ratio K

U3=KU=K (U in +U reverse)

Now let the partial pressure ratio K equal MR/LZc and add U3 and U1, U2 to get:

U4=U1+U3=KU into-KU reverse+KU into +KU reverse=2KU into

U5=U2+U3=-KU into +KU reverse+KU into +KU inverse=2KU counter

After the above proof a, b two points have been U into, U is separated into a point to U into, b to get U. The U input and the U reverse pass through the detection diodes respectively, and become a DC component. It is possible that the bipolar tube has a high frequency component at one end and the filter loop is changed to a PC low pass filtering method.

Two: production debugging and installation process

The printed boards of the two circuits of Fig. 1 and Fig. 3 are all 70 mm x 40 mm. Manually engraved using a single panel. Please refer to Figure 5:

In the figure, L1 in the high-frequency transformer is an enameled wire with Φ2.2mm, which directly penetrates the magnetic ring, and the two ends are respectively on the M-type socket. The square hole dug out from the center line of the printing plate is such that the magnetic lines of the magnetic ring are not shielded by the "ground" of the copper foil. The magnetic ring slides on the centerline and has the function of fine-tuning the inductance. It has an effect on the zero adjustment (REF).

The magnetic ring is matched with a double-hole magnetic ring of an antenna of a black-and-white television set. The double-hole ring is changed into a single-hole ring in advance, and the edge is removed and polished to be smooth. The magnetic ring of the resistance partial pressure (in FIG. 3) can be a magnetic ring having a magnetic permeability of 20 or Φ10. L2 is uniformly wound around 50T with an enamel wire of Φ0.15. The capacitor should have used a tubular dark blue high voltage capacitor, but it is hard to find now. A 60 volt monolithic capacitor is used herein. The high-turn circle can be used with the color code inductor, and the two-pole tube is used with the 1N60 and paired with the multimeter R*1K file. When hand-printing a printed board, pay attention to the symmetry of the lines. The trimming resistor used on the power meter should be soldered to the strip printed board beforehand and then fixed on the two long screws of the band switch. The potentiometer uses 2 watts. The head is 100 microamps.

The grounding of the printed board is made of Φ1.5mm copper wire, soldered to the screw of the M-type socket, and the grounding conductor of the circuit should be unified and soldered to the position of the center line of the printed board. Before commissioning, you should have a certain understanding of the circuit's composition. For example, Figure 1 is finally integrated into a bridge circuit, which is measured by the principle of balance, and Figure 6 is an electrical schematic.

Three: adjustment of the standing wave table

Figure 1 circuit adjustment:

In the figure, we want to balance the bridge. Because C1, C2 and R are fixed values, only the number of turns of the high-frequency coil L2 can be changed to balance the bridge. Some data emphasize that two voltage divider capacitors should be adjusted to balance the balance. Practice has proved that fine-tuning the voltage-dividing capacitors, although useful, is only a slight change, and the adjustment coil can greatly adjust the balance. The material of the magnetic ring is especially important here. I have tried several kinds of domestic magnetic rings. Some high-frequency magnetic rings can work at 29.6 MHz, but they are not working in the standing wave table.

After the balance is reached to a certain extent, the sharp point is gone. Repeated addition and subtraction of the number of turns is also invalid. How can the current of the REF file be adjusted to the zero position of the meter? (At this time, you can also find more magnetic rings.)

The circuit of Figure 1 uses a two-hole magnetic ring of a black-and-white TV antenna matcher, and it is better to change it into a single-hole magnetic ring. First, use a Φ0.15 enameled wire to wind 50T on the magnetic ring, and use the decreasing number of turns to find the zero point of the REF block.

Input 20 watts of CW signal from 7 to 14 MHz, and the output is terminated with a 40 watt 50 ohm dummy load. Each time a signal is injected, the RW is adjusted in the FWD file (forward) to make the meter full. Then, quickly hit the REF (reverse) to see where the hands fall back. If the pointer is too high, you can remove L2, re-write the forward gear and then input the CW signal, and use RW to adjust the fullness, and then hit the reverse gear to see the position of the hands. At this time, it will be found that the drop value is more than the first time, that is, the value of the hand movement to the left is large, and the distance from the zero position is small. This is the way to the head, and then you can repeat the last adjustment method. When the hands are pointing to about 5uA, slow down the speed and remove them one turn. In the adjustment, from time to time to change the position of the magnetic ring on L1, change its static attitude, which is the factor that affects the zero position, do not forget to adjust one of the porcelain fine adjustments at the same time, (small effect) Another porcelain fine tuning does not work. After repeated times, the hands can enter the zero value in the reverse gear position.