|COFDM versus QAM and VSB in ENG/ HD-ENG|
|The Real Deal on Single Carrier Solutions|
The discussion of COFDM versus VSB is not new to TV broadcasters in the US or in Europe. The choice of 8VSB as the digital standard in the United States was a hotly debated topic at the start of the DTV build-out, particularly after the Europeans demonstrated COFDM. The debate was centered on the fact that DVB-T’s COFDM transmission system performs substantially better in mobile applications, which some broadcast groups saw as a potential new revenue opportunity. In spite of the evidence, US broadcasters re-affirmed their choice of VSB, and the discussion appeared to be behind us. Some microwave vendors also chose VSB as an alternate to COFDM for high data rates, as required for airborne or stationary HD-ENG.
|Adjacent Channels and Offsets in COFDM Systems|
The Real Deal on spectral Issues
|Soon after the first ENG systems were put in service, carrier offsets became one of several new concepts developed to help fight adjacent channel interference in heavily congested areas. The intent was to enable an FM carrier to be offset by plus or minus half the distance from the channel center to the channel edge, to avoid interference in an adjacent 17 MHz channel. With a nationwide 2 GHz conversion to 12 MHz channels now underway, we are once again in the same situation with regard to avoiding interference, and once again carrier offsets are a hot subject, even though COFDM is far less susceptible to adjacent interference. MRC digital ENG systems have matured through several generations since their introduction in 1999, and we have considerable field experience and customer feedback where COFDM is involved.|
|Replacing Analog Links with Digital Links for STL or Intercity Relay|
|Things you need to know before you make a change!|
By the time we have reached the Sprint Nextel relocation deadline in 2007, hundreds of existing 2 GHz STLs and ICRs will be replaced to meet the new 12 MHz bandwidth requirements in the revised 2 GHz FCC band plan In the 7 and 13 GHz bands, ICR systems will be converted from analog to digital to support newly upgraded digital ENG central receive sites. When planning a change from analog to digital, it is important to understand the differences between the existing equipment and the replacements, and how the operating parameters may be affected.
|D-ENG Signal Quality Monitors|
The development of digital signal quality monitors for ENG has been a hotly debated topic since the first COFDM systems went on the air. News directors quickly learned about the digital “cliff”, and the arrival of this new knowledge was sometimes during a live broadcast. TV Engineers and news crews who had always relied on AGC as their golden yardstick soon discovered that their world had changed, and that a new way of monitoring must be found.
MRC manufactures several different types of strategic antenna systems. These antenna systems are typically or installed at a fixed location, are almost always receive systems, and in may also (in most cases) be set up as transmit or duplex systems.
This application note is intended to help the reader get an understanding of the various general types of video downlink systems available. For the sake of brevity, the systems discussed are digital, COFDM (Coded Orthogninal Frequency Division Multiplexing), systems. The same general principles can be applied to analog systems, as well, though these are decreasing rapidly in popularity for a variety of reasons.
There is a significant trend in the industry toward the use of IP interfaces in remote editing equipment utilized by broadcasters in the field. This is primarily due to the increased flexibility of the interface to do file transfer, storage and overall management of content with no degradation to video quality. Consequently, there is a secondary need to be able to transfer this IP data from the remote location over the remote path without changing formats
From the very beginnings of radio, engineers have been heavily focused on RF power output. While RF power level is certainly important in any transmission system, it is one of many factors that enter into the success formula. In long, medium and shortwave communications, propagation is not line of sight and is influenced by factors that can be difficult to predict, and more difficult to overcome, regardless of power levels. In microwave, most propagation effects are well understood and system performance can be accurately predicted under all but the most unusual conditions.