Jules Cohen Argues Against COFDM Switch, Warns of Three-Year Delay Risk
Summary
Engineer Jules Cohen defends 8VSB over COFDM, citing Charlotte indoor antenna tests where 8VSB outperformed NTSC reception in difficult locations. He warns that switching to COFDM would require extensive interference testing and potential reallocation of broadcast spectrum, causing a three-year delay.
"One aspect of a possible shift to COFDM is conveniently overlooked. The system could not be implemented for broadcasting without extensive testing of interference potential: to and from NTSC and interference between COFDM transmitters not carrying the same programs. Without such testing, we do not know whether the present allocations will work. The possibility exists that, with COFDM, we need a new allocation table. The result of a need for testing and reconsideration of allocations could mean a three-year delay."
Jules Coehn, P. E.
Jules Coehn, P. E.July 19, 1999 |
| Dale, thank you for the useful comments on 8VSB vs COFDM and the access to comments by Tsinberg and Williams. When we did indoor testing in Charlotte, we looked for households that actually used indoor antennas for NTSC reception. Our thinking was that one should not expect HDTV reception where NTSC cannot be received satisfactorily. We actually found two locations where NTSC was judged to be less than satisfactory, yet 8VSB performed well. I think Tsinberg is right. If enough demand for good indoor reception develops, the consumer electronics industry can produce a receiver that will do the job with 8VSB. We should not give up the advantage of 8VSB providing service at a lower S/N ratio than COFDM for what may be applicable for few viewers. Furthermore, as was the case with NTSC, I anticipate that receiver performance will improve with time. One aspect of a possible shift to COFDM is conveniently overlooked. The system could not be implemented for broadcasting without extensive testing of interference potential: to and from NTSC and interference between COFDM transmitters not carrying the same programs. Without such testing, we do not know whether the present allocations will work. The possibility exists that, with COFDM, we need a new allocation table. The result of a need for testing and reconsideration of allocations could mean a three-year delay. My opinion is that we should move forward as quickly as possible to establish the 8VSB digital service while encouraging the receiver manufacturers to move full speed ahead on improvements to their products. Jules Cohen, P.E. |
