dVMo uses advanced COFDM encoding techniques making it highly robust and resilient with excellent spectral efficiency. COFDM provides a dramatically enhanced link performance in the presence of multipath signals making it highly suited to mobile applications.

Key features of the dVMo product range are : -

• COFDM modulation
• Multi-service bearer with PAL or NTSC operation
• Transport stream input
• 100mW RF power output with optional higher power amplifiers
• Spectrally efficient, 2.5MHz or 7MHz as standard occupied bandwidths
• Synthesised frequency selection
• Diversity operation

Better Than Analogue ! 

Analogue video links, usually using frequency modulated (FM) transmission techniques have always suffered from the effects of multipath interference. This is the problem whereby the transmitted signal is scattered off objects en route to the receiver site and as a result arrives via slightly different radio paths at the receiver antenna.  In certain conditions these scattered signals can cancel each other out. This has the effect of degrading what might well have been a good quality transmitted video image.

There is a further disadvantage with traditional frequency modulated analogue links in that they are also very spectrally inefficient requiring some 25MHz or more of spectrum.

While the 100mW RF output may seem low, the enhanced performance over a conventional analogue link at the same power output will be most noticeable. The W&D team has produced a video CD of tests at 100mW and 1W at S Band which clearly shows the difference between the two modes. A copy of this CD which runs on PC platforms can be requested from our sales team 

How is this done ? 

The dVMo uses modern technology to overcome both of these problems.

Use of a COFDM modulation scheme with a MPEG CODEC results in a multipath immune spectrally efficient signal of only 7MHz occupied bandwidth. The coding process thrives on multipath situations making mobile camera operation a delight to watch.

Diversity Operation 

Because the signals transmitted are in digital format it is much easier to compare and check the quality of the received video when in a data format.  By using two receivers and comparing the data from each one, the optimum video data packet at any one time can be chosen and processed ensuring the optimum performance from the radio link.  This technique can be expanded to three or more receivers and is known as diversity reception.

MPEG2 Encoding 

The MPEG encoding module in the dVMo uses a protocol that is a dedicated derivative of the DVB-T standard. It converts the analogue video images into a serial data stream.  The encoder card has the facility to multiplex further external streams with the on board encoded video. This allows multiple videos to be carried down a single radio dVMo video link.

Encryption 

Digital encoding naturally adds a level of security to what is being transmitted and will stop an accidental interception of the transmission revealing what was in the video. For clients needing a more formal higher level of digital scrambling, encryption to AES128 or AES256 is available.

The Impact of Amplifiers 

Because of the complex nature of the COFDM signal, any amplification of the modulated signal must be very linear in its characteristics. Power amplifiers to boost the dVMo transmitter souces 100mW output will be relatively inefficient and therefore get hot and be bulky.

Heat and power consumption are important considerations when deploying dVMo hardware so users, particularly in covert applications or on UAV platforms, must consider the optimum system configuration to achieve physical range, battery economy etc. The W&D sales team can give support and advice on these aspects.

Frequency Options and Approvals 

The dVMo is available in various banded versions allowing coverage of the radio frequency spectrum from 300MHz to 6GHz

If as a client your application requires a full command and control system, then the dVMo can be integrated with W&D radio telemetry hardware. Please discuss your requirements with our sales team.