Wireless Video Transmission System (Hollyland / Teradek) High-Frequency Radio Interference Avoidance and DFS Channel Dynamic Switching

1. The pain of interruption in wireless video transmission of movies and TV shows: from “millisecond-level monitoring” to “full screen mosaic black screen”

In modern commercial shooting, directors, clients, and focus pullers all rely on wireless image transmission monitors hanging on their chests to control the scene in real time:

1. Physical linear propagation and penetration flaws of 5GHz microwaves:

• Most modern high-definition zero-latency wireless image transmission operates in the 5.1GHz to 5.8GHz ultra-high frequency microwave band;
• The wavelength is extremely short (only about 5 cm), and the diffraction ability (Diffraction) is extremely weak. Any human body, reinforced concrete load-bearing wall or even a dense crowd of photography assistants will cause severe physical shadow attenuation to the microwave signal (the human body contains 70% water and has a huge absorption loss for 5GHz radio!).

2. Vicious competition among multiple devices on the same frequency:

• At exhibitions, weddings or large office buildings, the hotspots of hundreds of mobile phones and high-power enterprise-level Wi-Fi routers in shopping malls are simultaneously filled with 5.8GHz conventional channels (channels 149~165);
• The signal-to-noise ratio of the image transmission receiver plummeted, and the screen suddenly erupted into violent digital mosaic fragments. The delay soared for several seconds. Finally, the screen went black and the connection was disconnected, causing the focus operator to lose focus and the customer to become furious.

2. DFS (Dynamic Frequency Selection) secret frequency band liberation

In order to escape the congested civilian Wi-Fi junk channels, professional wireless image transmission systems are generally equipped with DFS military-standard frequency band technology:

1. What is DFS Band:

• Exclusive airspace radio frequency bands between 5.25GHz to 5.35GHz and 5.47GHz to 5.725GHz;
• The International Radio Convention stipulates that this frequency band was originally reserved for national meteorological Doppler radars and military airport air traffic control radars. Ordinary household Wi-Fi routers are forced by law to strictly lock and disable this frequency band.

2. Dynamic Silent Listening and Avoidance Mechanism:

• After turning on DFS mode for professional image transmission, the chip will silently monitor the current channel for 60 seconds before transmitting a signal;
• After confirming that there are no military weather radar pulses around, you can legally borrow this open and pure "VIP military-grade high-speed channel"!

3. Practical profit:

• Thousands of civilian mobile phones and routers around are completely unable to access the DFS frequency band**. Image transmission exclusively enjoys the entire air corridor that is absolutely pure and free of any co-channel interference, and the penetration and connection stability are increased several times.

3. Professional on-site antenna layout and signal gain practical specifications

80% of the strength of the image transmission signal depends on the physical placement of the antenna:

1. The "donut" radiation physics field of Omni Antennas:

• The standard black omnidirectional antenna does not emit light from the tip of the antenna to the front. Its radio energy is a huge flat "doughnut ring" that spreads horizontally around the antenna pole with the antenna pole as the central axis**!
• Absolutely Prohibited: The tip of the antenna must never face the receiver! The tip direction is the "dead spot" with the weakest signal radiation intensity!
• Correct placement: The antenna poles of the transmitter and receiver must maintain parallel longitudinal and vertical orientations** in the three-dimensional space, so that the two donut energy radiation rings can achieve the maximum area of ​​frontal overlap and alignment.

2. Polarization Diversity: Two antennas are placed in a 90-degree "V" shape (Polarization Diversity):

• Tilt the two antennas on the receiver 45 degrees to the left and 45 degrees to the right respectively, forming a 90° orthogonal "V" shaped angle;
• Ensure that no matter whether the photographer places the camera horizontally, shoots vertically, or carries it on his shoulders while running at an angle, at least one antenna can achieve 100% vertical resonance reception with the electromagnetic polarization waveform of the transmitter.

3. Line-of-Sight absolutely high installation:

• The receiver must never be placed on the ground or stuffed in the director's backpack!
• Use magic-legged hands to raise the receiver to a height of more than 2.2 meters in the air, allowing the microwave signal to glide smoothly through the crowd's heads and completely cross the human body's water molecule absorbing wall, achieving 4K zero-latency, high-fidelity, silky-smooth monitoring from a hundred meters away.