چرا پیوندهای COFDM باید از فرکانس های DVB-T اجتناب کنند؟?

Why COFDM Links Should Avoid DVB-T Frequencies in Europe

COFDM (مولتی پلکسینگ تقسیم فرکانس متعامد کد شده) is a robust technology used for wireless video transmission. Its strong resistance to multipath interference makes it ideal for drones, وسایل نقلیه, and tactical surveillance systems.

با این حال, when operating in Europe, it is essential to avoid using frequencies assigned to DVB-T and DVB-T2 digital television broadcasting.
Even though both systems rely on the same COFDM modulation principle, their applications, قدرت انتقال, and regulatory control are completely different.

This article explains why COFDM links should avoid DVB-T frequencies, the consequences of overlap, and the recommended frequency bands for reliable and legal operation.

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1. Understanding DVB-T and DVB-T2

DVB-T (Digital Video Broadcasting – Terrestrial) و DVB-T2 are Europe’s standard formats for terrestrial digital TV broadcasting.

They occupy specific frequency bands:

• VHF Band III: 174 – 230 مگاهرتز
• UHF Bands IV–V: 470 – 694 مگاهرتز

Some regions previously extended up to 862 مگاهرتز, اما 700 MHz and higher range is now mostly reallocated to 4G/5G mobile networks. These frequency ranges are tightly regulated and reserved for high-power public television broadcasting.

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2. Why COFDM Transmitters Must Avoid DVB-T Frequencies

(1) Avoid Interference with Public Broadcasts

COFDM video transmitters working within 470–694 MHz may interfere with DVB-T reception nearby.
Because DVB-T transmitters use tens of kilowatts of power, even a low-power private transmitter can cause:

• pixelation or signal loss on TV screens,
• temporary blackouts of digital channels,
• complaints and enforcement actions by local authorities.

Agencies such as Ofcom (انگلستان), ANFR (فرانسه), و BNetzA (آلمان) strictly prohibit unauthorized signals within DVB-T frequencies.

(2) Prevent Receiver Overload and Self-Interference

Even if your COFDM system uses a different channel within the same band, strong DVB-T broadcast signals can saturate the receiver front end.
This leads to:

• drastically reduced transmission distance,
• unstable decoding,
• frequent image freezing or disconnection.

Thus, using DVB-T frequencies not only risks legal issues but also degrades your own link quality.

(3) Comply with Spectrum Regulations

Under جستجو EN 300 744 (DVB-T) و EN 302 755 (DVB-T2), the 470–694 MHz range is reserved exclusively for digital terrestrial television.
Operating COFDM systems in this range without authorization is illegal in most European countries and can result in fines or equipment seizure.

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3. Recommended Frequency Bands for COFDM Links

کاربرد	Recommended Band	Frequency Range	یادداشت ها
UAV / Drone Video	ISM Band	2.4 گیگاهرتز / 5.8 گیگاهرتز	License-free, globally accepted
Ground Surveillance	Licensed Band	1.4 گیگاهرتز / 2.3 گیگاهرتز	Balanced performance, license required
تاکتیکی / Police Use	Sub-GHz Band	300 – 900 مگاهرتز	نفوذ قوی, restricted access
Civil / Demo Use	ISM Band	2.4 گیگاهرتز / 5.8 گیگاهرتز	Best for demonstrations and non-critical use

Using these ranges prevents interference and ensures compliance with local spectrum laws.

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4. DVB-T/T2 Frequency Chart for Europe

باند	Frequency Range (مگاهرتز)	Primary Use
VHF Band III	174 – 230	Regional DVB-T broadcasting
UHF Bands IV–V	470 – 694	Core DVB-T/T2 range
بالا 700 مگاهرتز	694 – 862	Now used for LTE/5G mobile networks

For COFDM transmitters in Europe:

• Avoid: 174–230 MHz and 470–694 MHz
• استفاده کنید: 1.2 گیگاهرتز, 2.4 گیگاهرتز, یا 5.8 GHz bands for safe, interference-free video transmission.

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5. Engineering Recommendations

1. Add Selectable Frequency Options
   Allow users to manually switch to ISM bands or licensed frequencies to stay within legal limits.
2. Integrate RF Filters
   Bandpass filters help block powerful DVB-T signals and protect receiver sensitivity.
3. Provide Frequency Planning Tools
   Offer frequency charts and planning guides for each country to help users avoid restricted DVB-T/T2 ranges.
4. Include Legal Warnings in Manuals
   “Operation within DVB-T or DVB-T2 frequency ranges is prohibited in Europe. Use ISM or authorized frequencies only.”

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6. نتیجه گیری

COFDM offers exceptional reliability for wireless video transmission, اما frequency selection is critical.
In Europe, DVB-T/T2 occupies the 470–694 MHz band (and parts of 174–230 MHz) for digital TV broadcasting. Using these frequencies for COFDM video can cause interference, instability, and legal violations.

To ensure stable and compliant performance:

• Avoid DVB-T/T2 broadcast ranges,
• Use ISM or licensed frequency bands,
• Always verify local spectrum regulations before deployment.

Following these principles ensures clear video, stable communication, and compliance across Europe.

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