2 Way Walkie Talkie Radio Antenna
4 year ago
Yetnorson Antenna Co., Ltd.
8 year
Product details
Optimal antenna length of FM radio: accurate calculation logic based on FM frequency band.
The working frequency of FM radio covers 87-108MHz. Taking a typical 90MHz as an example, according to the electromagnetic formula "wavelength = speed of light/frequency", the corresponding wavelength can be deduced to be about 3.33 meters. Car Radio Antenna theory and engineering practice show that half wavelength (λ/2) or quarter wavelength (λ/4) is the ideal length for efficient signal reception;
λ/2 antenna: The length is about 1.66 meters, which is commonly used as an external Car Antenna for car radios. This design can directly resonate with FM band electromagnetic waves, capture radio signals 50 kilometers away in the open environment, and has the strongest anti-interference ability;
λ/4 antenna: The length is about 83 cm, and it is mostly used as the rod antenna of portable radio. At this time, Walkie Talkie Antenna is necessary to rely on the fuselage metal structure or external grounding plane (such as metal desktop) to form a complete resonant circuit. When the pull rod is stretched to 80-90 cm, it can stably receive signals within 20 km in urban environment.
Second, the technical code of Walkie Talkie Antenna length: resonance principle of 409MHz frequency band
The frequency band of 409-410MHz commonly used in civil walkie-talkies corresponds to a wavelength of about 73-74cm, and the relationship between antenna efficiency and length is more severe:
λ/2 antenna: 36-37 cm is the theoretical optimal length, at which the FM AM Antenna impedance has the highest matching degree with the signal source. The measured data show that the whip antenna with this length can achieve stable communication for 3-5 kilometers in the open field, and the signal attenuation after penetrating a concrete wall is only 20dB；.
Third, the antenna design boundary of civil walkie-talkie: the balance between scene requirements and technical compromise.
For civil walkie-talkies used in property and security scenes, the shortest critical value of antenna is 18 cm (λ/4), which is determined by two factors:
Physical threshold constraint: 18 cm is the minimum electrical length to maintain basic resonance in 409MHz band. Below this value, the signal strength will be exponentially attenuated due to "impedance mismatch". The actual measurement of a brand shows that the communication distance of 15 cm antenna is only 60% of that of 18 cm, and it can't even communicate across floors in underground garages and other scenes.
Engineering optimization scheme: In order to give consideration to portability, modern civil aircraft often adopt spiral loading technology-by winding the antenna into a spring shape, the equivalent electrical length of 36 cm can be achieved within a physical length of 15 cm. For example, the spiral antenna of a certain type of security walkie-talkie is only 12 cm after compression, but the resonance frequency is kept at.
409MHz, the measured communication distance can reach 2.5 kilometers, which meets the patrol needs of the park.
This design logic of "finding the optimal solution in physical laws" not only ensures the basic performance of professional communication equipment, but also alleviates the contradiction of portability through technological innovation, which has become the standard solution in the industry.
1. How long is the antenna of FM radio for the best effect? How to choose different scenes?
Answer: The optimal antenna length of FM radio (87-108MHz) is determined by the band wavelength:
Car scene: Choose a 1.66m λ/2 antenna (such as an external rod antenna), which can directly resonate with 90MHz electromagnetic waves, and can receive signals 50 kilometers away in the open, with the strongest anti-interference;
Portable scene: Using 83cm λ/4 rod antenna, it needs to cooperate with fuselage metal structure or external grounding plane (such as metal desktop). When stretched to 80-90cm, it can stably receive signals within 20km in the city.
2. What's the shortest antenna for civil interphone?
Answer: The shortest critical value of the antenna of civil walkie-talkie is 18 cm (λ/4), below which the signal will plummet due to impedance mismatch. In order to balance portability, modern models adopt spiral loading technology:
Technical principle: the antenna is wound into a spring shape, and the equivalent electrical length of 36 cm is realized within the physical length of 15 cm by increasing the inductance;
Example effect: the spiral antenna of a security intercom is only 12 cm, and the measured communication distance reaches 2.5 km, which meets the patrol demand of the park. At the same time, the standing wave ratio is controlled within 1.8 through electromagnetic parameter compensation to ensure the stable operation of the equipment.
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Yetnorson Antenna Co., Ltd.
Audited supplier
8 year
Main Product:
TV Antenna,
GPS Antenna,
GSM Antenna,
4G Antenna,
Wifi Antenna,
RF Cable
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