Indicators of the standing wave in the coil inductance
Many readers often question: how to see or measure a standing wave in the inductor? Accurate measurements of such wave may require considerable work, but it is possible to do and less accurate, but much simpler methods of such measurements. Their accuracy is usually sufficient for all Amateur radio task, while the frequency range of the coils can be quite large: 10 kHz .. 300 MHz.
To measure the standing wave will use the indicators of the electric field: at frequencies above 300 kHz they are much more sensitive and give much more accurate values and antinodes, for example, than the magnetic indicators or fluorescent lamps. Our task is to obtain the most accurate picture and antinodes, in this case, as little as possible interfering with the wave processes in the coil. To this end, our indicators should be of small size, consume low power and have no direct connection with the earth.
Most accurate but not the most convenient to use the indicator is presented in figure 1.1. In it, as the meter is the device М476/1 is the dial indicator from the tape. Of course, you can use another device, but the author М476 turned out to be optimal. For example, milliammeters, because of their smaller size and sensitivity, showed the worst results.
A more convenient indicator is shown in figure 1.2, and its constructive — in Fig. 1.3. Here is the gauge is applied to the led. The headline is very simple to manufacture and sufficiently accurate in dimension. The led should be chosen from the category of super bright, as usual — can not give the required sensitivity.
This indicator is quite simple. To the led podpisatsja bridge VD1-VD4, and two lower end — wiring with a length of 2-3 cm They are getting divorced at an angle of 20-30 degrees relative to each other. To the led and the bridge fits over the sleeve along its diameter, and from the positive output of the bridge wire is soldered 0.1 .. 0.3 mm, which is screwed onto sleeve top — the scheme is antenna A2. The length of this winding must cover the space from the led to the bridge. On the lower wiring is also worn sleeve: figure 1.3 it is depicted with a dotted line.
Bridge VD1-VD4 consists of four ultrafast diode with low capacitance. Very good results shown by the diodes 1N4148.
The presented design of the indicators though are optimal, but they can be done differently. Will be happy if you, our dear readers, send us your options.
How to measure?
Diagrams 1.1 and 1.2 shows two antennas. The first — the A1 is a couple of antennae that receive the electric field. When measuring, they should be drawn to the coil, and the animation shown in phantom by a green rectangle. The distance from the gauge to the coil you adjust visually depending on the field strength and the luminosity of the led. The second antenna A2, in General, is a solitary capacity. To strengthen this capacity, you can simply hand in her fingers.
Below are interactive stand clearly visualizes the measurement process. By default, there is a quarter-wave coil, but you can choose other values. An indicator led, you can move the mouse from right to left. From his position over the coil depends on the level of illumination. It also defines points and antinodes of the electric field in the coil. Here it is assumed that the left end is grounded.
The multiplicity of wavelengths in the coil: