Published: TV Technology

Issue:  10/23/97



(Sidebar to Viacom Story)



Understanding OET-69





As part of it's on-going DTV transition plan, the FCC's Office of Engineering and Technology 

(OET) issued bulletin number 69 on July 2, 1997.  Its purpose is to provide guidance on the 

implementation and use of the Longley-Rice methodology for evaluating TV service coverage 

and interference of NTSC and DTV stations. 



The Longley-Rice radio propagation model is used to predict radio field strengths for DTV 

coverage at specific geographic points, based on the elevation profile of terrain between the 

transmitter and each specific reception point. 

 

OET-69 is divided into four parts and provides the following information:



* Section I defines the formulas and factors used in conjunction with the F(50,50) curves 

specified for calculating both the analog and digital channels. Replication of the NTSC coverage 

pattern is discussed along with the Longley-Rice computer methodology itself.



* Section II outlines a method for evaluating interference to the service areas of both analog 

NTSC and DTV stations.  The interference criteria used for co-channels, adjacent channels and 

the UHF Taboo channels are also defined in several field strength charts. 

  

* Section III addresses the use and implementation of the FCC's Longley-Rice Computer 

program and describes the evaluation procedure for calculating transmitter distances and 

antenna gain.



* Section IV consists of a very short list of answers to Frequently Asked Questions (FAQ sheet) 

with regard to the Longley-Rice methodology.



Due to the large number of reception points that must be individually examined, a computer is 

needed to make these predictions.  The Longley-Rice program was written in Fortran code and is 

available on the FCC's Internet website at : 



ftp://ftp.fcc.gov/pub/Bureaus/Engineering_Technology/Databases/mmb/dtv/flr.zip--Joe Fedele