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The USA solves mobile DTV reception problems

Apr 1, 2003 12:00 PM, Brad Dick editorial director

             

For several years, the USA has been unable to even consider business applications that rely on digital TV mobile receivers because 8-VSB modulation couldn't handle the rapidly changing multipath and signal levels. Now that has all changed. The backers of the Zenith solution, ATSC, have announced new and far-ranging improvements to the 8-VSB transmission platform. Does DVB-T now have a competitor?

Broadcast Engineering was recently privy to a series of secret tests on the latest improvements to 8-VSB chips for mobile reception. These new chips have been specifically designed to improve the capture and display of 8-VSB signals in mobile environments. Let's look at just a couple of the test results. A glossary of terms is listed below.

The first mobile reception test was designed to measure the Barrington Angular Reception Factor (BARF) constant. A human reception model, shown above, was used to avoid any metal reflections from the automobile. The subject engineer was loaded with about 19kgs of electronics and wore a head-mounted antenna to minimize body shielding. After an hour of experiments, the test subject finally did BARF. So much for this improvement.

The test subject then walked a 16:9 grid pattern. At each crosspoint, the Circular Radiation And Polarization (CRAP) factor was measured. This analysis looks at how effective reception is when the person or vehicle is moving in a clockwise direction. The same test is useful when the receiver moves counterclockwise, but that wasn't measured in these tests. The results were as expected. On a scale of 1 to 10, the new ATSC improvements were full of CRAP and rated a 10.

Unfortunately, the electric component of the magnetic sinusoidal waveform was often absent. This meant that the CRADT measurement went off the scale. At these locations, the engineer was instructed to apply first the HYB correction mode for 30 seconds. If that didn't improve the reception, the HAP mode was applied for 60 seconds. Unfortunately, these corrections seldom worked. These test locations were identified on the test grid as CRADT 1 through 22.

Because of the high number of CRADT results, a second round of tests was conducted. These tests were restructured to measure just CEGADS, sometimes called “C-GADS”. Researchers felt that this was probably going to be a bottom-line performance measurement anyway, so identifying it early might prove beneficial.

Test results, while encouraging in flat-plain environments such as parking lots, were less so anywhere near a building, tree, light pole or moving dog. Also, as the subject walked clockwise around the grid, FFHD image was visible, but it rotated clockwise on the screen. The only way to stabilize the image was for the subject to walk counterclockwise around the grid. Finally, if the test subject passed near any building or car, the CRAP hit the fan, and the FFHD was totally unviewable.

We are awaiting a new round of tests, which are to be conducted just after the NAB convention.

I hope readers enjoyed my April Fool's story.

Send comments to: • editor@primediabusiness.com • www.broadcastengineering.com

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