External Camera Wireless Video Transmission (Wireless Video Transmitter) DFS Dynamic Frequency Selection and 5GHz Band Radar Avoidance

1. The microscopic battlefield in the 5GHz frequency band: Why does image transmission have to compete with radar for the runway?

In order to transmit zero-delay and uncompressed high-definition video (requiring huge bandwidth from 20MHz to 80MHz), modern wireless image transmission generally works in the 5GHz open ISM radio frequency band (5.150GHz ~ 5.850GHz):

• Extreme congestion on common non-DFS bands:
• The low frequency band (Band 1 / CH 36-48) and the high frequency band (Band 4 / CH 149-165) are open frequency bands for civilian use;
• Hundreds of mobile Wi-Fi, Bluetooth, and civilian drones are all crowded here, and the signal-to-noise ratio is extremely low, resulting in a sharp reduction in image transmission distance and frequent screen freezes;
• Pure Arcadia: DFS Band 2 / CH 52-140:
• The signal in this spectrum is pure and free of any consumer-grade Wi-Fi interference. It is a golden channel for image transmission to achieve ultra-long distance transmission through walls of hundreds of meters;
• Deadly National Security Conflict: Radar and Life Safety Red Lines:
• This golden frequency band, in the national radio spectrum allocation, is the core backbone frequency band of the national meteorological Doppler radar, military air defense radar and civil airport terminal weather radar (TDWR)!

2. DFS (Dynamic Frequency Selection) mandatory physical avoidance legal mechanism

According to the mandatory standards of radio laws in various countries, any wireless transmitting equipment working in the DFS frequency band must have a strict Radar Detection Self-Destruction Protocol (Dynamic Frequency Selection, DFS) built in:

[Step 1: Power-on Availability Channel Check (CAC: Channel Availability Check)] 
After the video transmission is turned on, [it is absolutely prohibited to transmit video signals immediately]! 
The receiving chip must continue to monitor the live space in silence for a full 60 seconds (CAC countdown), 
Make sure there is no weak radar pulse signal of even 1 microsecond in the surrounding area before allowing open transmission! 
│ 
▼ (If a nearby radar pulse scan is detected midway) 
[Step 2: Forced frequency hopping and 30 minutes of penalty silence (In-Service Monitoring & NOP)] 
Once the image transmission detects the radar signature pulse: 
Must [forcibly cut off current channel transmission (Instant Blackout)] within 200 milliseconds! 
And the channel is automatically blacklisted by the system, and the channel is locked and punished by being silent for 30 minutes and is absolutely prohibited from being used again! 

This is the fundamental physical reason why when you are filming around the airport, the video transmission will suddenly black out without warning and freeze, and you will never be able to connect back within half an hour!

3. Film and television crew on-site disconnection prevention and channel tactical configuration SOP

1. High-risk geographical environment investigation (list of restricted areas):

• The shooting location should be within a radius of 15 kilometers** from a civil/military airport;
• The shooting positions are located around the radar tower of the Meteorological Observatory and large maritime ports;
• When operating in the above areas, Auto frequency selection must be completely turned off in the image transmission menu and manually forced to lock on the non-DFS frequency band (such as CH 36-48 or CH 149-165)! We would rather tolerate a little civilian interference than resolutely avoid triggering the DFS mechanism and causing sudden death and interruption during shooting.

2. Indoor or safe studio away from radar:

• Decisively open DFS channels (such as CH 100 to CH 128);
• Complete the 60-second CAC automatic listening scan 3 minutes before power-on to ensure that the frequency band is in an absolutely stable locked state when recording is officially started;

3. Directional Antenna (Panel Antenna/Mushroom Head Antenna) Layout:

• The transmitter and receiver antennas are strictly prohibited from being perpendicular to each other! All glue stick antennas must be kept strictly parallel to each other in terms of spatial geometry (Polarization Alignment);
• A high-gain flat directional antenna is used on the monitor side to align it with the camera's motion trajectory, which can increase the signal-to-noise ratio by an additional 10dB and completely suppress surrounding clutter.

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