پارامترهای فرستنده ویدئو COFDM توضیح داده شده است

Complete Explanation of COFDM Video Transmitter Parameters

Understanding FREQ, BW, FEC, GI, نقشه, توجه کنید, 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 (نمایش روی صفحه). A typical example might look like this:

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

---

FREQ — Frequency

Full Name: فرکانس عملیاتی
مثال: FREQ: 830MHz

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

چگونه کار می کند:
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, نفوذ بهتر از موانع.
• 1.2 GHz, 2.4 GHz, یا 5.8 GHz for short-distance, higher data rate transmission.

Impact:

• Lower frequency (به عنوان مثال, 700-900 مگاهرتز): Better penetration and longer range, ideal for drones or mobile units in urban areas.
• Higher frequency (به عنوان مثال, 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.

---

BW — Bandwidth

Full Name: پهنای باند کانال
مثال: BW: 2MHz

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

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

Explanation:

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

Example comparison:

Bandwidth	نرخ داده	محدوده	Suitable For
1 مگاهرتز	کم	طولانی ترین	Low bitrate or SD video
2 مگاهرتز	متوسط	طولانی	HD video over long distance
4 مگاهرتز	بالا	متوسط	High-quality HD or low-latency video
8 مگاهرتز	Very High	کوتاه	Close-range or line-of-sight applications

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

---

FEC — Forward Error Correction

Full Name: تصحیح خطای فوروارد
مثال: FEC: 2/3

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

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

تفسیر:

• 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.

مثال:
For long-distance drone transmission, FEC = 1/2 یا 2/3 is ideal.
For short-range, high-quality streaming, you can use 3/4 یا 5/6.

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

---

GI — Guard Interval

Full Name: گارد فاصله
مثال: 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, وسایل نقلیه, 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 (به عنوان مثال, 1/4): Better resistance to echoes, ideal for urban or complex terrain, but slightly reduces data rate.
• Shorter GI (به عنوان مثال, 1/32): Higher speed, suitable for open field or direct line-of-sight links.

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

---

MAP — Mapping (نوع مدولاسیون)

Full Name: Constellation Mapping یا نوع مدولاسیون
مثال: 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:

تلفیق	Bits/Symbol	نرخ داده	Signal Tolerance
QPSK	2	کم	عالی
16QAM	4	متوسط	متوسط
64QAM	6	بالا	کم

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

---

ATTEN — Attenuation

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

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

چگونه کار می کند:

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

Effect:

• Lower attenuation (به عنوان مثال, 0 دسی بل): maximum power, longest range.
• Higher attenuation (به عنوان مثال, 10 دسی بل): reduced power, useful for short-range testing or avoiding interference.

مثال:
When testing indoors, set ATTEN to 10–20 dB to prevent saturating the receiver.
For actual flight or field use, استفاده کنید 0 دسی بل to maximize range.

---

UART — Universal Asynchronous Receiver/Transmitter

مثال: 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 نرخ باد — the communication speed between the transmitter and the controlling device.

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

هدف:

• Parameter configuration (فرکانس, قدرت, پهنای باند, و غیره)
• Firmware upgrades
• Status feedback (قدرت سیگنال, دما, و غیره)

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

---

EVNE — Even Parity

مثال: EVNE یا EVEN

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

Options:

• EVEN (EVNE): حتی برابری
• ODD: Odd parity
• هیچ کدام: No parity bit

تابع:
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.

---

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 (فرکانس, پهنای باند, FEC, GI, and modulation) match correctly.

If it shows “Unlocked” or “No Lock”:

• Check that both devices have the same فرکانس, پهنای باند, FEC, GI, و مدولاسیون.
• 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.

---

Summary Table

پارامتر	Full Name	مثال	تابع	Key Effect
FREQ	فرکانس	830 مگاهرتز	Sets RF operating frequency	Must match TX/RX
BW	Bandwidth	2 مگاهرتز	Defines channel width	Affects data rate & محدوده
FEC	تصحیح خطای فوروارد	2/3	Adds redundancy for reliability	Balances speed & ثبات
GI	گارد فاصله	1/32	Reduces multipath interference	Shorter GI = higher speed
نقشه	نقشه برداری مدولاسیون	QPSK	Sets modulation scheme	Impacts throughput & signal robustness
توجه کنید	تضعیف	0 دسی بل	Adjusts transmit power	Higher ATTEN = lower power
UART	Serial Interface	19200	Communication port	Used for control & راه اندازی
EVNE	Even Parity	EVEN	UART parity setting	Prevents serial errors
Channel Lock	-	Locked/Unlocked	RF synchronization status	Must lock before video output

---

سوالات متداول (پرسش و پاسخ)

---

نتیجه گیری

Understanding these COFDM parameters is essential for getting the best performance from your wireless video system.
Each setting—FREQ, BW, FEC, GI, نقشه, توجه کنید, UART, EVNE—affects how your transmitter balances between محدوده, ثبات, and video quality.

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

• FREQ: within 700–900 MHz
• BW: 2 مگاهرتز
• FEC: 2/3
• GI: 1/16
• نقشه: QPSK
• توجه کنید: 0 دسی بل

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