剛剛做了一個無線電頻率（RF）遙控器，遙控器由發射器和接收器組成。
這個是在2009或2010年做的一個無線電頻率（RF）遙控器：
下麵是Gemini介紹的RF：
Radio Frequency (RF) refers to electromagnetic waves that lie within a specific portion of the electromagnetic spectrum. This spectrum encompasses a wide range of frequencies, from very low frequencies (VLF) to extremely high frequencies (EHF).
Frequency is a measure of how often a wave repeats itself in a given time. It is typically measured in Hertz (Hz), which represents one cycle per second.
- RF waves are characterized by their frequency.
- Different frequencies within the RF spectrum have different properties and uses.
- Lower frequencies tend to have longer wavelengths and can travel farther distances.
- Higher frequencies have shorter wavelengths and are better suited for carrying more data.
Common uses of RF:
- Telecommunications: Radio, television, cell phones, Wi-Fi, and satellite communications all utilize RF waves.
- Radar: Radar systems use RF waves to detect and track objects.
- Remote control: Remote controls for devices like TVs and garage doors use RF signals.
- Medical imaging: MRI (Magnetic Resonance Imaging) uses RF waves to generate images of the human body.
- Heating: Microwave ovens use RF waves to heat food.
市場上可以買到不同頻率的RF的發射器和接收器模板， 通常有315 MHz和433 MHz的,
我用 433 MHz 的發射器和接收器模板。市場上的RF的發射器和接收器模板：
下麵是Gemini解釋RF怎樣傳播信號：
Radio Frequency (RF) carries a signal by generating electromagnetic waves through an antenna, which then transmit the information encoded onto a high-frequency carrier wave, allowing the signal to travel through the air to a receiver antenna that converts the waves back into an electrical signal that can be decoded and processed; essentially, the antenna acts as a transducer between electrical signals and radio waves, enabling wireless transmission of data.
- The source of the RF signal, which generates a carrier wave and modulates it with the desired information (like voice, video, or data) using techniques like amplitude modulation (AM) or frequency modulation (FM).
- The antenna acts as the interface between the electrical signal and the electromagnetic waves, converting the electrical signal into radio waves that can propagate through the air.
- The radio waves travel through the air, potentially reflecting off obstacles depending on the frequency and environment.
- The receiving device with an antenna that captures the radio waves and converts them back into an electrical signal, which is then demodulated to extract the original information.
計算用於某頻率的天線長度（源於Gemini）：
For 433 MHz transmission and reception, a common and effective antenna length is 1/4 wavelength.
Here's how to calculate the approximate length:
-
Find the wavelength:
- Wavelength (λ) = Speed of light (c) / Frequency (f)
- c (speed of light) ≈ 3 x 10^8 meters/second
- f (frequency) = 433 MHz = 433 x 10^6 Hz
- λ = (3 x 10^8 m/s) / (433 x 10^6 Hz)
- λ ≈ 0.69 meters
-
Calculate 1/4 wavelength:
- 1/4 λ ≈ 0.69 meters / 4 ≈ 0.17 meters ≈ 17 centimeters
Therefore, a good starting point for an antenna length at 433 MHz is around 17 centimeters.
Note: This is an approximate value. Actual performance can be influenced by factors like antenna type (e.g., dipole, monopole), antenna design, and the specific application.
Common antenna types for 433 MHz:
- Helical antennas: These are often used for their compact size and reasonable performance.
- Whip antennas: Simple and easy to construct, they are commonly used in many applications.
- Dipole antennas: These provide good performance but are typically larger than other types.
用於433 MHz 的天線為17 cm.
這是幾天前做的：
照片上麵的是發射器，下麵的是接收器，紅色LED是接收到了發射器發出的信號。
RF遙控器與IR遙控器比較：
RF的遙控器可以比IR（紅外）遙控器（電視，照相機等）傳播更遠，紅外遙控器隻能在5米內有效，RF遙控器可以傳播10米或更遠，第一張照片裏最右邊的433 MHz的發射模板可以傳到理論上的4.3公裏。
應用：
1. 照相機的快門和閃光。
2. Drone的控製。
3. 機器手的控製。
4. 電機速度的控製。
5. 車庫門的控製。
6. 汽車門的控製。
7. 汽車遠程開動的控製 等等。
