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The standard output from the range of dVMo radio transmitter units is 100mW. This power level while seemingly low is in fact very effective over surprisingly long distances. It has become generally accepted that one tenth of the RF output power is needed in a well designed COFDM radio link compared to that would have been needed with a conventional analogue link to acheive the same picture quality.
Notwithstanding the above, it will occassionally be necessary to boost the transmitted signal to a higher RF power output level than 100mW. First choice and most cost effective choice in such circumstances is to look at the antennas in use at both the transmit and receive locations. A ten fold increase in effective radiated power through antenna gain is sometimes easier to achieve if the circumstances suit.
Having discounted or being unable to change antennas leaves little option but to add a RF power amplifier to the system design.
As mentioned elsewhere in the dVMo section, a DVB COFDM transmission is a highly complex transmission that depends on its ultimate performance on the ability to measure changes in the radio signal being received. If by adding a radio power amplifier these small changes have their characteristics changed or distorted through any non linearities introduced into the transmission chain then performance will degrade dramatically.
In practice, without using very complex and relatively inefficient techniques to linearise a RF power amplifier, the next best solution is to greatly underun the amplier. This will ensure it has plenty of headroom and is running over a small but more linear part of its transfer characteristic. Typically this requires an 8 to 10dB back off.
The impact of this backing off means a need for 1Watt output will require a 10W rated amplifier and so on. This will have size and power consumption implications which must be considered by the system engineers on the project.
A product that offers a performance that appears to ignore these simple rules should be regarded with some suspicion. Use of such a poorly rated device will lead to an effect called spectral re-growth and the spreading of the COFDM signal into adjacent spectrum.
The dVMo-PA1 boosts 10mW of RF output to 1W. Its high quality and low distortion make it suitable for use with any COFDM modulation. The dVMo-PA1 is self contained and does not require fan cooling. Power supply is a wide ranging floating supply from 9V to 36V.
Different versions can be ordered to suit the frequency range in use.
The dVMo-PA5 boosts 10mW of RF output to 5W. Its high quality and low distortion make it suitable for use with any COFDM modulation. It runs from nominal 12V or 28V DC supply. Different versions can be ordered to suit the frequency range in use.
The amplifier can be remotely turned on and off and is protected by self-resetting, over- temperature shutdown. Remote and on-panel indicators are provided for shutdown and RF output present.
Note that for the reasons already mentioned in this section, the dVMo-PA5 is a 50W device running in linear Class A mode. It is therefore dissipating a great deal of heat and for this reason the cooling is fan assisted. For some applications this may not be appropriate and this should be considered by the client's system engineering team.
The dVMo-PA10 is a higher power output variant of the dVMo-PA5. It is also fan-cooled and will boost 50mW of RF output from a dVMo-T transmitter unit to 10W.
A number of different versions and frequency ranges are available for the dVMo-PA units and they can be offered with 12V and 28V DC supplies. Airframe mounting variants are available on request. As ever please consult the Sales team at W&D for more advice on your application.
For other versions or specific requirements please contact our Sales Team
on +44 (0)118 981 1444
