HK1066326B - Am antenna noise reducing - Google Patents

Description

Amplitude modulated antenna with reduced noise

Technical Field

The present invention relates generally to wireless antenna noise reduction, and more particularly to novel apparatus and techniques for reducing interference noise in the AM band with AM (amplitude modulated) antennas.

Background

Operation of an electrical power controller, such as a triac shutter, may generate severe interference noise in the AM wireless band. The interference noise may enter the radio wave through any of capacitive structures coupled to the antenna, through inductance of the AC mains (mains), or magnetic substances coupled to the antenna. In home use, the primary mode is through the AC mains.

Typical antennas for AM are either external or internal loop types, such as ferrite rod loop AM antennas. External loop antennas typically use twisted pairs of antenna inlets connected to balanced inputs. The inner ferrite rod loop antenna is generally unbalanced with one end of the loop at RF ground and the other end connected to a varactor. Unbalanced detector coils are commonly used to power up detector Integrated Circuits (ICs).

It is an important object of the present invention to reduce electrical interference in AM radio with an improved antenna.

Disclosure of Invention

According to the present invention, there is provided a loop antenna having: the two ends of the winding structure are connected to the input end of the radio frequency amplification circuit; a varactor structure connected to the winding structure.

Drawings

Other features, objects, and advantages will become apparent from the following description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic circuit diagram of a center grounded ferrite rod loop antenna in accordance with the present invention;

fig. 2 is a schematic circuit diagram of a grounded-end ferrite rod loop antenna in accordance with the present invention.

Detailed Description

Referring to FIG. 1, a schematic circuit diagram of one embodiment according to the present invention including a center grounded ferrite rod loop antenna is shown. The circuit comprises a ferrite rod 11 having a resonant circuit winding 12 and a detector winding 13. One end of the resonant circuit winding 12 is directly connected to the varactor tuning diode 14 and the other end of the winding 12 is coupled to the varactor diode 14 through a low impedance coupling capacitor 15. The intermediate tap 16 of the resonant circuit winding 12 is coupled to a reference potential via a low impedance coupling capacitor 17. The reference potential is assumed to be grounded for the remainder of the disclosure, but it should be noted that the reference potential may be set to any desired potential. The intermediate tap 16 also receives a tuning voltage through a resistor 18 for controlling the effective capacity of the varactor 14 to tune the resonant circuit to the frequency of the desired AM carrier. The junction (junction) of the varactor diode 14 and the low impedance capacitor 15 is connected to ground through a resistor 21. Representative parameter values are given in fig. 1. A low impedance bypass capacitor 22 connects the end of the pickup (pickup) winding 13 that receives the bias voltage for the detector integrated circuit input to ground. The other end of the detector winding 13 is connected to the input of the detector integrated circuit.

The embodiment of fig. 1 balances the antenna circuit by placing the RF ground in the center of the resonant circuit winding 12. The center tap 16 is preferably offset from the physical center of the winding 12 due to the effect of the unbalanced detector coil 13 and the capacitance to the external environment of the conductor attached to the input of the detector integrated circuit. The position of the intermediate tap 16 should be offset from the centre of the winding coil and can be determined experimentally to obtain the maximum interference reduction. In this example, the center tap 16 is located 16 turns (turns) from the capacitor end of winding 12 and 31 turns from the varactor end in a 220-micro-shared inductor, and winding 13 has 24 turns and 55-micro-shared inductance to provide 27dB of improvement in line-on interference rejection.

It is possible to remove the coil 13 of fig. 1. In this case, a suitable intermediate point is located along the coil 12, where the RF signal can be tapped. This point is chosen such that the coil impedance matches the input impedance requirements of the circuit connected to this intermediate tap, i.e. the RF input of the detector IC typical of said circuit.

Referring to fig. 2, another embodiment of the invention is shown which includes coil 12A and coil 12B which form resonant windings, with their opposite terminals held at RF ground by capacitors 15A and 15B, respectively, to balance the antenna. Each winding provides the correct driving point impedance for the detector integrated circuit, so the detector coil 13 is not necessary. Thus, the input to the detector chip is now taken directly from the junction between windings 12A and 12B, which are held at the same RF potential by capacitor 22A. The side effects of parasitic capacitance can be reduced by adding conductive structures to the circuit, such as geometric structures formed in Printed Circuit Board (PCB) copper. As shown in fig. 2, an additional trace wire 23 is added to the hot side of winding 12B and the take path is taken as close as practically possible along its entire length to the lead connected to the RF input of the detector IC. The minimum distance between the leads and the added structure is determined by the PCB design rules for designing and manufacturing the PCB. The rules are selected based on cost and performance requirements. Smaller phase separation distances generally provide better system performance in terms of reduced parasitics at a higher cost. In the present invention, a 0.006 inch pitch is achieved.

The additional copper structure 23A at the end of this line also compensates for side effects caused by the capacitance of the conductor connected to the input of the detector integrated circuit. In a particular form of this embodiment, each winding 12A and 12B has 24 turns.

New apparatus and techniques have been described for significantly reducing unwanted noise into the antenna circuit of an AM radio. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the apparatus and techniques disclosed herein without departing from the inventive concepts. Thus, the invention is to be construed as embracing each and every novel feature and novel combination of features provided in and possessed by the apparatus and techniques herein disclosed and not limited solely by the spirit and scope of the appended claims.

Claims (9)

1. A tunable AM wireless antenna in the form of a ferrite rod loop antenna, comprising:

a ferrite rod having a resonant structure forming a balanced antenna circuit, wherein the resonant structure has a first winding structure (12A) and a second winding structure (12B) surrounding the ferrite rod, each winding structure having an inner end and an outer end relative to a rod end; the method is characterized in that:

a varactor (22A) tuning structure providing a controllable capacitance between an internal terminal of the first winding structure and an internal terminal of the second winding structure,

a DC path comprising the second winding structure (12B) connected to the varactor diode (22A), the DC path being constructed and arranged to provide a tuning signal to the varactor diode,

wherein an outer end of the first winding structure (12A) is configured to receive an external signal and an inner end of the first winding structure is connected to an external detection circuit; and is

The outer end of the second winding structure (12B) is constructed and arranged to receive the tuning signal.

2. The tunable AM wireless antenna according to claim 1, wherein the external terminals of the first winding structure (12A) and the second winding structure (12B) are held at a reference potential at radio frequency.

3. The tunable AM wireless antenna according to claim 2, wherein the reference potential is a circuit RF ground.

4. A tunable AM wireless antenna according to any of claims 1 to 3, wherein the second winding structure (12B) is directly coupled to the varactor diode (22A) and the first winding structure (12A) is coupled to the varactor diode (22A) by a capacitor.

5. A tunable AM wireless antenna according to any of claims 1 to 3, wherein the inner end of the second winding structure (12B) is further connected to a conducting structure (23A) to minimize interference effects.

6. A tunable AM wireless antenna according to claim 5, wherein the electrically conductive structure (23A) is a geometric structure formed in a printed circuit board with trace lines.

7. A tunable AM wireless antenna according to claim 5, wherein the electrically conductive structure (23A) is physically located within a predetermined distance from the structure that electrically couples the internal end of the first winding (12A) to the input of the RF detector circuit.

8. The tunable AM wireless antenna of claim 6, wherein the tracking line is connected to an internal end of the second winding structure (12B).

9. The tunable AM wireless antenna of claim 7 wherein the predetermined distance is a minimum tracking distance on a printed circuit board.