Paramètres de l'émetteur vidéo COFDM expliqués

Complete Explanation of COFDM Video Transmitter Parameters

Understanding FREQ, PC, FEC, GI, CARTE, ATTENTION, UART, EVNE, and Channel Lock

When customers receive a COFDM video transmitter, they often notice a set of technical parameters displayed on the screen or OSD (Affichage à l'écran). A typical example might look like this:

For many users, especially those who are not radio engineers, these values look confusing. Cependant, each of them plays a crucial role in how the COFDM transmitter sends stable, low-latency video over long distances.
This article explains all these parameters in detail, what they stand for, and how to adjust them correctly for your application — whether you are using COFDM transmitters for drones, véhicules, or tactical video systems.

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FREQ — Frequency

Full Name: Fréquence de fonctionnement
Exemple: FREQ: 830MHz

This shows the RF center frequency used by the transmitter. It defines where in the radio spectrum the video signal is transmitted.

Comment ça marche:
The transmitter modulates the digital video signal into an RF carrier. The receiver must tune to the exact same frequency to demodulate and decode the video.

Typical frequency ranges:

• 300–900 MHz for long-range, meilleure pénétration à travers les obstacles.
• 1.2 GHz, 2.4 GHz, ou 5.8 GHz for short-distance, higher data rate transmission.

Impact:

• Lower frequency (par ex., 700–900 MHz): Better penetration and longer range, ideal for drones or mobile units in urban areas.
• Higher frequency (par ex., 5.8 GHz): Higher throughput, but shorter range and more easily blocked by buildings.

Practical Tip:
Always make sure the transmitter and receiver use exactly the same frequency. Even a 1 MHz difference will cause the receiver to lose lock.

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BW — Bandwidth

Full Name: Bande passante du canal
Exemple: BW: 2MHz

Bandwidth defines how wide the transmitted signal is on the frequency spectrum. It determines how much data (vidéo + contrôle) can be transmitted at once.

Common values: 1 MHz, 2 MHz, 4 MHz, 8 MHz.

Explication:

• UN wider bandwidth allows more data throughput, enabling higher-resolution or higher-frame-rate video.
• UN narrower bandwidth uses less spectrum and provides longer range and stronger penetration, but at the cost of data speed.

Example comparison:

Bande passante	Débit de données	Gamme	Suitable For
1 MHz	Faible	Le plus long	Low bitrate or SD video
2 MHz	Moyen	Long	HD video over long distance
4 MHz	Haut	Moyen	High-quality HD or low-latency video
8 MHz	Très élevé	Court	Close-range or line-of-sight applications

Practical Tip:
For drone or tactical applications, 2 MHz is often the best balance between range and quality.

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FEC — Forward Error Correction

Full Name: Correction d'erreur directe
Exemple: FEC: 2/3

FEC adds redundant information to the transmitted signal so that the receiver can detect and correct errors caused by noise, ingérence, or weak signal conditions.

Typical ratios: 1/2, 2/3, 3/4, 5/6.

Interprétation:

• 1/2 → Strong error protection (half of the data is error correction).
• 5/6 → Weaker error protection but higher throughput.

Effect on performance:

• Lower FEC ratio = more reliable link, less data rate.
• Higher FEC ratio = faster data rate, needs strong signal.

Exemple:
For long-distance drone transmission, FEC = 1/2 ou 2/3 is ideal.
For short-range, high-quality streaming, vous pouvez utiliser 3/4 ou 5/6.

Practical Tip:
If your video occasionally freezes or breaks under weak signal, try lowering FEC to 1/2.

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GI — Guard Interval

Full Name: Intervalle de Garde
Exemple: GI: 1/32

A guard interval is a short pause inserted between COFDM symbols to prevent inter-symbol interference caused by reflections or multipath signals.

Why it matters:
In real-world environments, radio signals bounce off walls, véhicules, or the ground, creating multiple delayed copies of the same signal. Without a guard interval, these reflections would overlap and corrupt the next symbol.

Typical values: 1/4, 1/8, 1/16, 1/32.

Effect:

• Longer GI (par ex., 1/4): Better resistance to echoes, ideal for urban or complex terrain, but slightly reduces data rate.
• Shorter GI (par ex., 1/32): Higher speed, suitable for open field or direct line-of-sight links.

Exemple:
If you’re transmitting through buildings or around corners, set GI to 1/8 ou 1/16.
If it’s a clear open field, 1/32 works fine.

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MAP — Mapping (Type de modulation)

Full Name: Constellation Mapping ou Type de modulation
Exemple: MAP: QPSK

MAP defines how binary data (0s and 1s) are mapped onto the carrier wave — essentially, which modulation scheme is used.

Common modulation types:

• QPSK (Quadrature Phase Shift Keying): Transmits 2 bits per symbol; very stable, suitable for weak signals and long range.
• 16QAM: Transmits 4 bits per symbol; higher throughput, but needs strong signal.
• 64QAM: Transmits 6 bits per symbol; maximum data rate but most sensitive to noise.

Effect:

Modulation	Bits/Symbol	Débit de données	Signal Tolerance
QPSK	2	Faible	Excellent
16QAM	4	Moyen	Modéré
64QAM	6	Haut	Faible

Practical Tip:
For long-range, mobile, or drone systems, QPSK is the best option.
If your system is fixed and the signal is strong, 16QAM can improve throughput.

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ATTEN — Attenuation

Full Name: Transmit Power Attenuation
Exemple: ATTEN: 0dB

This parameter adjusts the output RF power de l'émetteur.
Attenuation simply means how much the signal is reduced before transmission.

Comment ça marche:

• 0 dB = full output power (no reduction).
• Higher dB value = signal power reduced by that amount.

Effect:

• Lower attenuation (par ex., 0 dB): maximum power, longest range.
• Higher attenuation (par ex., 10 dB): reduced power, useful for short-range testing or avoiding interference.

Exemple:
When testing indoors, set ATTEN to 10–20 dB to prevent saturating the receiver.
For actual flight or field use, utiliser 0 dB to maximize range.

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UART — Universal Asynchronous Receiver/Transmitter

Exemple: UART: 19200

UART refers to the serial communication interface used to configure or control the COFDM module through a data cable or host controller.

19200 represents the débit en bauds — the communication speed between the transmitter and the controlling device.

Common baud rates: 9600, 19200, 38400, 115200.

But:

• Configuration des paramètres (fréquence, pouvoir, bande passante, etc.)
• Firmware upgrades
• Status feedback (force du signal, température, etc.)

Practical Tip:
When connecting to a PC or microcontroller, ensure both ends use the same baud rate and parity settings (see “EVNE” below).

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EVNE — Even Parity

Exemple: EVNE ou EVEN

This refers to the parity bit used in UART communication. It’s a simple form of error detection that ensures data integrity.

Possibilités:

• EVEN (EVNE): Even parity
• ODD: Odd parity
• AUCUN: No parity bit

Fonction:
Parity bits help detect transmission errors during serial communication.
If the parity doesn’t match between the transmitter and the connected device, data may appear as random symbols.

Practical Tip:
Set the same parity (EVEN/ODD/NONE) on both devices to ensure stable communication.

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Channel Lock

Display Example: “Channel Lock” or “Lock OK”

This message indicates that the receiver has successfully locked onto the transmitter’s COFDM signal — meaning all parameters (fréquence, bande passante, FEC, GI, and modulation) match correctly.

If it shows “Unlocked” or “No Lock”:

• Check that both devices have the same fréquence, bande passante, FEC, GI, et modulation.
• Verify antennas are properly connected.
• Ensure signal strength is above the threshold.

Once “Channel Lock” appears, the receiver can decode the video and output stable image.

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Summary Table

Paramètre	Full Name	Exemple	Fonction	Key Effect
FRÉQ	La fréquence	830 MHz	Sets RF operating frequency	Must match TX/RX
PC	Bande passante	2 MHz	Defines channel width	Affects data rate & gamme
FEC	Correction d'erreur directe	2/3	Adds redundancy for reliability	Balances speed & stabilité
GI	Intervalle de Garde	1/32	Réduit les interférences par trajets multiples	Shorter GI = higher speed
CARTE	Cartographie des modulations	QPSK	Sets modulation scheme	Impacts throughput & signal robustness
ATTENTION	Atténuation	0 dB	Adjusts transmit power	Higher ATTEN = lower power
UART	Serial Interface	19200	Communication port	Used for control & installation
EVNE	Même parité	EVEN	UART parity setting	Prevents serial errors
Channel Lock	—	Locked/Unlocked	RF synchronization status	Must lock before video output

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Foire aux questions (FAQ)

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Conclusion

Understanding these COFDM parameters is essential for getting the best performance from your wireless video system.
Each setting—FREQ, PC, FEC, GI, CARTE, ATTENTION, UART, EVNE—affects how your transmitter balances between gamme, stabilité, and video quality.

For most long-range drone and tactical video applications, the following configuration is recommended:

• FRÉQ: within 700–900 MHz
• PC: 2 MHz
• FEC: 2/3
• GI: 1/16
• CARTE: QPSK
• ATTENTION: 0 dB

With correct configuration and antenna alignment, COFDM technology can provide robust, faible latence, non-line-of-sight video transmission in challenging environments.