The VHF/UHF Dual cast Digital Transpores/Digital Transmitters sets a new standards for ATV and DVB-T/H gap filler and transposer technology by combining top performace with an extensive number of features second to none. The equipment is characterized by the use of an internal advanced FPGA digital board able to satisfy all functionality related to DVB-T network. The digital echo canceller function increases the potential output power of the gap filler by automaticcally suppressing feedbacks from the transmitting to the receving antenna. The echo canceller is futhermore capable of cleaning up the primary input to the gap filler. By using the web- interface management system all the functions can be set and monitored.The RF Signal, coming from the digital board, is boosted by an internal power amplifier solid state daseign for optimal performance in both digital and analogue broadcast application. The equipments is able to operate in the frequency band VHF band III and UHF band IV & V. Size and weight have been reduced to obtain a compact unit. The improved performance has been achieved by means of an advanced approach in the design, focusing on low power consumpion and on excellent linearity over the entire operational band. High reliability is mainily guaranteed by using a limited number of transistors to achieve a given power target and by using over dimensioned cooling devices: broadcasters can thus reduce their long-term system costs. The echo canceller reduce the power level of self-induced echoes (feedback from TX-antenna radiating back into RX-antenna) as well as echo present in the original input signal (arising either from multi path reception condition or different arrival times of the main-signal stemming from simultaneous reception of different base-station).
The objective of the echo cancelling functionality is to ease installation, improve usable output power level and hence repeater coverage, and improve quality of service by “cleaning up” the input signal prior to transmission. The primary benefit of using the echo canceller on a repeater site is, that the system will become stable even with a negative gain margin-allowing more power to be transmitted from the site. The echo canceller will operate under steady state lab condition with a negative gain margin approaching 25 db. The actual improvement of the gain margin for a given site will depend on several site related condition, but typically an improvement in gain margin in the order of 10dB will be achieved.
The algorithm of the echo canceller constantly tracks and adjust for dynamic changes in the signal conditions – thereby optimizing performance under changing condition. Echoes occurring within the “cancelling window” will be suppressed in absolute power, in the output signal of the digital repeater. The size of “cancelling window ” can be configured to either 7msec (default) or 14msec for an 8 MHz system bandwidth.
