Many broadcasters, including Sinclair, have become increasingly concerned about the ability of digital television signals to be received by portable and mobile receivers. One of the characteristics of 8VSB receivers up to now has been the relatively long lock-up time and the fussiness of indoor antennas typical in urban situations. Mr. Arnold echoed the concerns of his company that a TV signal, whether digital or analog, has to be easy to receive, and that the consumer is not going to put up with the need to make lots of adjustments in the process.
As an outgrowth of this concern, Sinclair tested for ease of reception between 8VSB and COFDM in the Baltimore area. An STA was obtained to operate a 50KW station on channel 40 and Sinclair assembled enough equipment to produce comparable 8VSB and COFDM signals on that channel, including a Zenith 8VSB modulator and a Rohde & Schwartz COFDM modulator. A common RF chain was used with the output of either modulator switched into the exciter. Several dozen receive sites, both close in and at distances of several miles, were visited, both indoor and outdoor. Typical consumer set-top bowtie antennas were used for reception of the channel 40 signals close-in, and yagis were used for the distant sites. Production model 8VSB receivers by Panasonic and Pioneer were used, along with NDS and Nokia COFDM receivers, made for the European market and modified for the 6 MHz channel. The transmitter and receive equipment was carefully calibrated and checked at the beginning and end of each day's run, and results were tabulated.
Analysis of the data showed that out of 31 sites using a single bow-tie antenna, 8VSB reception was possible at only eight, while COFDM came in at all 31. At 18 sites using a double bow-tie antenna, all sites received a COFDM signal while only se ven 8VSB sites did. Another parameter, ease of reception, was determined by rotating the receive antenna and noting the azimuth range over which a usable signal was produced. COFDM exhibited much greater robustness in this measure, with over 30 opportunities receivable regardless of antenna orientation, compared with 24 opportunities in which 8VSB was receivable at all.
Mr. Arnold emphasized that there is no "hidden agenda" behind
Sinclair's investigation of COFDM. The group has 58 television stations
facing conversion to DTV and they feel their efforts would be wasted if
the transmission system did not allow for easy reception by the public.
Over 400 stations are in support of its petition asking the FCC to allow
stations to choose whether they use 8VSB or COFDM.