JPH0297005A - variable inductance - Google Patents

Abstract

PURPOSE:To obtain an improved highly reliable high frequency coil capable of stable and precision frequency setting and facilitating adjustment operation by providing a support member having a threaded hole coaxial with an air-core coil and rotatably mounting an adjusting screw in the threaded hole. CONSTITUTION:A support member 1 having a threaded hole 3 is provided coaxially with an air-core coil 5 and an adjusting screw 2 is rotatably mounted in the threaded hole 3. For example, by using a shielding case 1 for the support member for the adjusting screw 2, the air-core coil 5 is designed beforehand to be disposed in the vicinity of the shielding case 1. The air-core coil 5 is fixed to a circuit board 4 at a soldering part 6, and further, copper foil 7 on the rear surface of the circuit board 4 and the shielding case 1 are fixed to each other by soldering 8. Then, the threaded hole 3 is provided at the point where the extension of the central axis of the air-core coil 5 intersects the shielding case 1, and the electrically conductive adjusting screw 2 is inserted into the threaded hole 3 and the spacing between the front end of the screw and the nearest winding end of the air-core coil 5 is changed from the outside by rotating the adjusting screw 2 utilizing a screwdriver.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to variable inductance, and more specifically,
This invention relates to variable inductance for high frequencies used in oscillation, tuning, and resonant circuits in the shortwave band, very short wave band, and very short wave band.

[Prior art] Generally, in coils for high frequencies below the shortwave band, the magnetic flux density inside the coil is increased by providing a material with higher magnetic permeability, such as an iron core or ferrite core, than in the case of an air-core coil. By doing so, sufficient inductance can be obtained even with a small coil. In this case, when adjusting the inductance, the magnetic flux density changes by changing the position of the core within the coil, so the inductance can be easily adjusted.

Above the short wave band, the magnetic flux density does not necessarily increase due to the demagnetizing field caused by eddy current in bulk materials such as iron cores, and the magnetic aftereffect effect in ferrite.
At frequencies above 0MHz, air-core coils are used exclusively.
Sufficient inductance can be obtained even with a relatively small number of turns.

When a high-frequency coil is used for purposes such as resonance, tuning, and oscillation, the coil and capacitor constitute a tank circuit.As is well known, the frequency f of the tank circuit is given by the following equation.

f = 1 / (2π f σ ) where L is the inductance of the coil, and C is the capacitance of the capacitor.

In frequency adjustment, it is common to keep the inductance L of the coil constant and to vary the capacitance flc using a trimmer capacitor or the like.

On the other hand, there is a method in which the frequency is adjusted by keeping the capacitor capacitance tc constant and changing the coil inductance L. For frequencies below the shortwave band, it can be easily adjusted by changing the position of the core inside the coil, but this method cannot be used for air-core coils for frequencies above the shortwave band, so it is difficult to adjust the coil shape, such as the number of turns, winding diameter, and pitch. There is a way to change the points.

A method of changing the pitch of a general air-core coil as an adjustment of a high-frequency coil will be explained using FIG. 2. If the circuit is surrounded by a shield case for the purpose of noise removal, as shown in Fig. 2(a), an adjustment hole lO should be provided to allow the adjustment driver 9 to go in and out. Inductance can be reduced by inserting it between the windings and widening the interval between the cutting lines as shown in FIG. 2(b).

[Problem to be solved by the invention] In recent years, high-density mounting methods have been adopted in high-frequency circuits as transmission lines can be significantly shortened, and trimmer capacitors are relatively large components, so it is difficult to implement high-density mounting. This is inconvenient. For this reason, it is advantageous to make the inductance (2) variable in high frequency circuits in the short wave band or higher.

In the method of adjusting the frequency by changing the inductance L of the coil, it is necessary to change the shape of the air-core coil, such as the number of turns, the winding diameter, and the pitch.
There are problems such as accurate adjustment is difficult and time consuming, and changes over time are large.

For example, when adjusting by changing the coil diameter and number of turns,
- It is necessary to remove the coil attached to the board and replace it with a coil with an appropriate winding diameter and number of turns.

However, since coil parts have large variations in inductance, using this method requires a lot of effort to replace them, and precise adjustment is also difficult.

The method of changing the pitch of the coil does not require replacing the coil, but precision adjustment requires skill, and since the coil is forcibly deformed, the pitch may return and the adjusted frequency may shift, causing instability. Not only this, but also fluctuations occur due to vibrations and shocks.

This invention was devised to overcome this problem, and by providing an inductance adjustment mechanism in the high-frequency air-core coil, frequency setting can be performed stably and precisely, and the adjustment work can also be simplified. Our goal is to provide excellent high-frequency coils with high reliability.

[Means for solving the problem] The present invention provides a support for supporting and further fixing a screw on an extension of the air-core coil in the coaxial direction of the coil, and a screw hole is provided in a portion facing the coaxial center of the coil. Insert a conductive screw made of metal or other material into the screw hole so that the tip of the screw faces the coil.

[Operation] According to the present invention configured as described above, an eddy current is generated inside the screw made of a conductive material by the high frequency alternating magnetic field generated from the coil, and a countermagnetic field is generated. Since the demagnetizing field caused by the eddy current becomes large enough to not be ignored in the frequency band above the short wave band, the magnetic flux density interlinking with the coil decreases. This reduces the inductance of the coil, thereby increasing the oscillation frequency.

By changing the relative position of the screw and the coil, the frequency increase can be adjusted accurately.After adjustment, the screw can be fixed to the support with adhesive, solder, welding, etc. to adjust the external environment. It will operate stably even in the face of fluctuations.

According to this invention, a high-frequency coil has excellent effects such as stabilizing the oscillation frequency of high-frequency waves such as communication equipment, reducing variations between products, and achieving high reliability in the operation of various equipment. can be provided.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 shows an embodiment of the present invention, and FIG.
A front view is shown in the same figure (b).

In this embodiment, a shield case 1 used for noise countermeasures in high frequency oscillation circuits is used as a support for the adjustment screw 2.

The air-core coil 5 is designed in advance to be placed near the shield case 1. The air-core coil 5 is fixed to the circuit board 4 by soldering using the part 6, and is further fixed to the copper foil 7 on the back side of the circuit board 4. By fixing the and shield case 1 with soldering 8, the influence of the surroundings on the air-core coil 5 is fixed.

A screw hole 3 is provided at a point where an extension of the coaxial center of the air-core coil 5 and the shield case 1 intersect. For the screw hole 3, a female thread may be cut into the through hole, or a nut may be fixed with adhesive.
The purpose of this screw hole is to insert and support a conductive adjustment screw 2. Thereby, by turning the screw head of the adjustment screw 2 from the outside with a screwdriver, the distance between the tip of the screw and the spring of the air-core coil 5 can be changed.

[Effects of the Invention] When the adjustment screw is brought closer to the air-core coil, the oscillation frequency increases, and when it is moved away from it, it decreases. Since the oscillation frequency is the lowest when the adjustment screw is removed, it is necessary to design the inductance of the air-core coil to be large in advance so as not to exceed the target oscillation frequency in this state.

The support body to which the metal screws are attached can be replaced by a shield case often used in high frequency circuits, and can be used particularly in applications where it is desired to exclude external noise such as local oscillation circuits. Since the screw head protrudes outside the case, it has the advantage of being able to be readjusted even if the inductance changes due to the influence of the metal case after the circuit is sealed in the case.Furthermore, in this case, when adjusting with a trimmer capacitor etc. In comparison, there is no need to provide a hole in the shield case for adjusting the degree through which the driver passes, and the shield case can be completely sealed, thereby preventing intrusion of external mF. Therefore, it is suitable for high frequency oscillation circuits such as CO, which are extremely sensitive to external noise and require stability and highly accurate setting.

In the example shown in Fig. 1, the target oscillation frequency is 360M.
In terms of Hz, it is possible to adjust approximately IMH2 with one rotation of the adjustment screw, allowing precise adjustment with an accuracy of 10KI-Tz.

If a magnetic material such as iron is used for the adjustment screw, unnecessary radiation will increase due to the effects of nonlinear distortion and Barkhausen noise, resulting in deterioration of the C/N ratio and S/N ratio. Good results can be obtained by using magnetic materials.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, with FIG. 1(a) being a partial side sectional view and FIG. 1(b) being a front view. Figure 2 is a partial side sectional view showing the previous adjustment method;
Figure a) shows the state at the time of adjustment, and figure (b) shows the state after adjustment 6 1... Shield case, 2... Adjustment screw, 3...
Screw hole, 4... Circuit board, 5... Air core coil, 6...
...Soldering is part, 7...Copper foil, 8...Soldering is part,
9...adjustment driver, 10...adjustment hole (a) (b) Fig. 1

Claims (1)

[Claims] A variable inductance characterized in that a support body provided with a screw hole is provided on an extension line of an air-core coil in a coaxial direction of the coil, and an adjustment screw is rotatably attached to the screw hole.