02.23.2004 12:00 AM
FCC Releases Updated OET Bulletin 69
As reported in the February 9 RF Report, the FCC has released an updated version of FCC Office of Engineering and Technology (OET) Bulletin 69. The updated version is now available on the FCC OET Bulletins On-Line web site. I downloaded the new version and compared it with the old version. As noted in the News Release announcing the revised bulletin, the changes are mostly editorial.

The section "Evaluation of Service," including field strengths and planning factors, is unchanged except that the Media Bureau Consolidated Database System (CDBS) is now used as the reference for directional antenna relative field data instead of the FCC Directional Antenna Data Base. Links to FCC sources of DTV azimuthal pattern data are provided.

The "Evaluation of Interference" section has the most changes. As noted in the news release, the D/U ratios have been corrected to agree with those in the FCC Rules. The D/U ratios for DTV into Analog interference changed from -17 dB to -14 dB for a lower adjacent (-1) analog channel and from -12 dB to -17 dB for an upper adjacent (+1) analog channel. The co-channel D/U ratio was unchanged. The new version also notes, "The D/U ratios for co-channel interference to DTV service in Table 5A are only valid at locations where the signal-to-noise ratio is 28 dB or greater for interference from DTV and 25 dB or greater for interference from analog TV service. At the edge of the noise-limited service area, where the signal-to-noise (S/N) ratio is 16 dB, the co-channel D/U ratios are 21 dB and 23 dB for interference from analog TV and DTV, respectively." The updated OET-69 also provides a formula to compute the minimum D/U ratio at locations where the DTV S/N ratio is greater than 16 dB but less than 28 dB. Table 5B in the old OET-69 is now Table 5C and a new Table 5B lists "Minimum Co-channel D/U Ratios for Analog Interference to DTV".

In the section "The FCC Longley-Rice Computer Program", the new version provides a link to the FORTRAN code used to evaluate new proposals. Interestingly, in the subsection "Outline of Evaluation Procedure", item 3 has been changed from "The coordinates of 1990 census blocks falling inside each cell..." to "The coordinates of census blocks falling inside each cell..." The reason for this change was not explained, but perhaps it is to allow use of 2000 census data. The last change noticed was replacement of the analog into digital and digital into digital maximum distances from Table 7, "Culling of Undesired Stations" with "NC" for all except first adjacent and co-channel cases.

Finally, the "Frequently Asked Questions" section at the end of the Bulletin was dropped.

Like the original version, the updated OET-69 did not mention how Longley-Rice Error Code 3 cells are to be treated nor did it mention that the FCC FORTRAN FLR program incorrectly calculates depression angle in many cases. See the Comments of Hammett and Edison, Inc. in the Docket 87-268 biennial review dated August 26, 1999 for more information on these issues. .


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