30 09, 10 22:23
On August 17, NAB unveiled an impressive high tech report they had commissioned from a not well known, but very well qualified military contractor on a possible replacement for the ubiquitous “rabbit ears” used in houses that depend on over-the-air reception. It is commendable that in an effort to reverse the decline in over-the-air viewers NAB this time decided to pay for good engineering rather than the usual lawyers and lobbyists.
You blogger noticed during multiple visits to Japan during the analog TV era that actual TV reception in Japanese homes was almost always much better than in US homes even though both countries used the same NTSC transmission system. Multiple inquiries revealed a tentative conclusion that Japanese homeowners buy new TV sets every few years from a neighborhood dealer (denkiyasan) and that as part of the package they get professional installation and maintenance of an outdoor antenna. Americans, by contrast, usually buy TVs from a large store which at best offers delivery to the doorstep and thus rely on either poorly maintained outdoor antennas or “rabbit ears”. Of course, many Americans used CATV but until those systems started having major fiber optic components in the past few years, users several amplifiers away from the cable headend were at the mercy of their cable company’s maintenance schedule. (Lack of attention to amplifier gain adjustments resulted in overloading of later amplifiers and generation of intermodulation distortion in the system, degrading the delivered picture quality. These problems generally disappear in systems with a fiber optics backbone.) Now with DTV, over-the-air viewers don’t see a “snowy” signal, but due to the “cliff effect” you may not see any signal at all! Thus winning back over-the-air viewers needs simple but effective home antenna technology.
MegaWave Corp., of Devens, MA had done a study for NAB in 1995 on available antenna technology for improved set top performance and NAB’s FASTROAD (Flexible Advanced Services for Television & Radio On All Devices) program, a technology advocacy program, hired them again to survey new antenna technology and the opportunities resulting from decreased TV band spectrum. (MegaWave’s hometown is next to Ft. Devens, for many years a major Army Security Agency installation. So it can be surmised that they have dealt with “3 letter agencies” other than FCC.)
The report is fascinating for us techies, reviewing all sorts of interesting antenna technologies not well known outside of antenna researchers and the military industrial complex. The pictures at the top of this post shows one antenna they spent a lot of effort exploring and its performance.
The report points out than many advanced technologies depend on feedback from the DTV receiver on how well it is receiving the signal. In 2007 CEA developed a standard (CEA-909) for such signals from the DTV receivers to the antenna, but receivers with this interface are rare in the US market. In Europe, a comparable interface is more common. (One wonders if the recent spat between NAB and CEA over FM receivers in cell phones will make this type of interindustry cooperation any easier.)
The MegaWave report ends with these conclusions:
- There have been significant and potentially useful antenna design methods and actual hardware developed over the past 15 years that will improve the performance of low‐profile, compact indoor/set‐top DTV antennas.
• In the area of electro‐magnetic computational and design optimization methods Genetic Algorithms (GA) and the Central Force Optimizer (CFO) have proven themselves as powerful tools in the design of broadband, compact antennas.
• Using the above, we have included an example of an advanced antenna technology, specifically the Fragmented Antenna as part of this project. We submit that it would be nearly impossible for a human to replicate its design and performance.
• The Non‐Foster active broadband matching technology and its required semiconductors have matured to the point where they could be incorporated into a commercial indoor/set‐top design to provide a matched antenna where it is considered as being electrically small. In the example shown below it would be used to provide acceptable performance with the Fragmented dipole within the 54‐88 MHz band. Other element geometries are also possible.
• Many of the other advancements listed in Table 1‐1, specifically 2.4 through 2.6, require a CE‐909‐A type interface with the DTV receiver, and while potentially useful if and when manufacturers start adding this feature to their products they offer no practical improvement for the near term.
• The technologies designated as 2.7 through 2.10 while interesting are either too embryonic (2.7 & 2.8), too complicated and too large (2.10) or not well vetted (2.9) to be considered in the near term.
Congratulations to NAB for this technological tour de force.