COFDM Video Transmitter Parameters Explained

Complete Explanation of COFDM Video Transmitter Parameters

Understanding FREQ, PN, FEC, IG, MAP, ATTEN, 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 (Exibição na tela). A typical example might look like this:

For many users, especially those who are not radio engineers, these values look confusing. Contudo, 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, veículos, or tactical video systems.

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FREQ — Frequency

Full Name: Frequência operacional
Exemplo: FREQ: 830MHz

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

Como funciona:
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, melhor penetração através de obstáculos.
• 1.2 GHz, 2.4 GHz, ou 5.8 GHz for short-distance, higher data rate transmission.

Impact:

• Lower frequency (por exemplo, 700–900 MHz): Better penetration and longer range, ideal for drones or mobile units in urban areas.
• Higher frequency (por exemplo, 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: Largura de banda do canal
Exemplo: BW: 2MHz

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

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

Explanation:

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

Example comparison:

Bandwidth	Taxa de dados	Faixa	Suitable For
1 MHz	Baixo	Mais longo	Low bitrate or SD video
2 MHz	Médio	Longo	HD video over long distance
4 MHz	Alto	Médio	High-quality HD or low-latency video
8 MHz	Muito alto	Curto	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: Correção de erro de encaminhamento
Exemplo: FEC: 2/3

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

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

Interpretation:

• 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.

Exemplo:
For long-distance drone transmission, FEC = 1/2 ou 2/3 is ideal.
For short-range, high-quality streaming, you can use 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: Intervalo de guarda
Exemplo: 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, veículos, 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 (por exemplo, 1/4): Better resistance to echoes, ideal for urban or complex terrain, but slightly reduces data rate.
• Shorter GI (por exemplo, 1/32): Higher speed, suitable for open field or direct line-of-sight links.

Exemplo:
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 (Tipo de modulação)

Full Name: Constellation Mapping ou Tipo de modulação
Exemplo: 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:

Modulação	Bits/Symbol	Taxa de dados	Signal Tolerance
QPSK	2	Baixo	Excelente
16QAM	4	Médio	Moderado
64QAM	6	Alto	Baixo

Practical Tip:
For long-range, móvel, 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
Exemplo: ATTEN: 0dB

This parameter adjusts the output RF power do transmissor.
Attenuation simply means how much the signal is reduced before transmission.

Como funciona:

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

Effect:

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

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

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UART — Universal Asynchronous Receiver/Transmitter

Exemplo: 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 taxa de transmissão — the communication speed between the transmitter and the controlling device.

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

Propósito:

• Configuração de parâmetros (freqüência, poder, largura de banda, etc.)
• Firmware upgrades
• Status feedback (intensidade do sinal, temperature, 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

Exemplo: 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.

Opções:

• EVEN (EVNE): Paridade uniforme
• ODD: Odd parity
• NENHUM: No parity bit

Função:
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 (freqüência, largura de banda, FEC, IG, and modulation) match correctly.

If it shows “Unlocked” or “No Lock”:

• Check that both devices have the same freqüência, largura de banda, FEC, IG, e modulação.
• 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

Parâmetro	Full Name	Exemplo	Função	Key Effect
FREQ	Freqüência	830 MHz	Sets RF operating frequency	Must match TX/RX
PN	Bandwidth	2 MHz	Defines channel width	Affects data rate & faixa
FEC	Correção de erro de encaminhamento	2/3	Adds redundancy for reliability	Balances speed & estabilidade
IG	Intervalo de guarda	1/32	Reduces multipath interference	Shorter GI = higher speed
MAP	Modulation Mapping	QPSK	Sets modulation scheme	Impacts throughput & signal robustness
ATTEN	Atenuação	0 dB	Adjusts transmit power	Higher ATTEN = lower power
UART	Interface serial	19200	Communication port	Used for control & configurar
EVNE	Even Parity	EVEN	UART parity setting	Prevents serial errors
Channel Lock	-	Locked/Unlocked	RF synchronization status	Must lock before video output

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Perguntas frequentes (Perguntas frequentes)

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Conclusão

Understanding these COFDM parameters is essential for getting the best performance from your wireless video system.
Each setting—FREQ, PN, FEC, IG, MAP, ATTEN, UART, EVNE—affects how your transmitter balances between faixa, estabilidade, and video quality.

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

• FREQ: within 700–900 MHz
• PN: 2 MHz
• FEC: 2/3
• IG: 1/16
• MAP: QPSK
• ATTEN: 0 dB

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