[opendtv] Time for the 30 foot reference critics to put up or shu t up

John Willkie wrote (in his usual colorful fashion):

>I've heard many people over the years on this list -- Craig Birkmaier, Frank 
>Eory, Dermot, Bob Miller, Tom Barry (just to name a few) criticize the FCC's 
>use of a 30-foot high reference for measurement of tv (and, by inference, FM) 
>signal levels.
>Now is the time that separates the girls from the women.  The FCC has an open 
>proceeding -- as mentioned in Harry C. Martin's column in the most recent 
>Broadcast Engineering -- where they are asking whether they should change 
>their 
>signal measurement criteria for distant TV signals.  The proceeding is to 
>implement changes in the SHVIA, but they are using it as a launch pad for a 
>few 
>other things.
>
>So, If any of the above are serious on this point -- of which I doubt in many 
>ways -- now is the time to propose something different.  The FCC isn't asking 
>for mere whiny opinions -- they want studies, and they want reasons to change 
>things.
>
>Time to s**t or get off the pot on this topic.  I suspect that inaction on the 
>critics part will be the result, but I will remind each and every critic of 
>the 
>30 foot critera when and if this silly criticism arises in the future that, 
>once again, they had a chance to do something other than imitate Onan.

My view on this has not changed and has always been very simple: *IF* the 
assumed use model of DTT (or any other broadcast service) is exclusively based 
on outdoor rooftop antenna reception, then 30-foot signal level reference 
measurements are all that are needed. *IF* the requirements also include indoor 
set-top reception and/or other use models like pedestrian portable and mobile, 
then additional signal level measurements are needed that are somewhat 
representative of those other use models -- otherwise there is no way to 
properly create link budgets for those other reception scenarios.

In the absence of additional field strength measurements, all we have are 
studies that provide guidelines or bounds on signal attenuation vs. elevation 
below 30 feet or signal attention as a function of various building materials. 
Some of this was discussed in the VSB ad-hoc group's final report.

Since those other reception scenarios -- especially indoor set-top reception -- 
are expected to some degree, it might be valuable to generate signal strength 
contours for each TV market that represent field strength at, say, 5 feet HAAT 
and with some nominal attenuation for the prevailing building materials of the 
area (brick vs. stucco, etc.). The FCC can only use one set of numbers for DTV 
planning, and they have done so with the 30 foot numbers. But a broadcaster 
might be interested to know how his field strength contours change for indoor 
vs. 30 foot outdoor reception.

Zenith, the FCC and others have used these concepts to some extent in DTV field 
testing -- taking not only reference measurements at 30 feet, but also at lower 
elevations (FCC used set-top antennas on a 6 foot tripod) and sometimes 
indoors. But again this is after the fact -- the planning was done years ago, 
and was only based on 30 foot measurements. 

The FCC can choose to change their signal measurement criteria or not, but 
unless they change the DTV Planning Factors and Table of Allotments, it isn't 
going to matter one iota to a viewer who cannot get indoor set-top reception 
and is unable to install a rooftop antenna (the Mark Schubins of the world).

-- Frank 


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