Definitions of "Grade A" "Grade B" signals

[Markxxx]

I never really thought about it, but does anyone have the actual definitions of what a "Grade A signal" is? Or what is a "grade B signal" is?

Do the stations or the FCC determain this? I know what I think it means, but does anyone have the "acutal definiton" Like suppose "grade a" means the signal comes in 90% of the time, or what ever?

Thanks.

I noticed some maps of TV stations also list another grade called "city grade" is this anything official?

 

[stationi]

I found this on a legal web site ...

"For a variety of regulatory purposes, the FCC has developed and uses various definitions and standards of signal intensity. A signal of only Grade B intensity is expected to produce a good picture at least 90 percent of the time at the best 50 percent of receiver locations or sites. The Grade B contour is an imaginary line, generally in the shape of a circle of which the transmitter site is the center, which marks the outer limits of the area within which a signal of Grade B or better intensity is expected. A stronger Grade A signal should produce a good picture 90 percent of the time at the best 70 percent of receiver locations. The Grade A contour, which encompasses the area within which such a signal is expected, is also generally a circle, but a smaller one that lies wholly within the Grade B contour. A so-called city-grade signal should produce a good picture 90 percent of the time at 90 percent of receiver locations; its outer limits are the city-grade contour which encompasses a still smaller area."

 

[vibe]

won't most of this be moot by 2/28/2009? Many people have had to rely (if they don't have cable/satelite) with OTA reception from distances considerably beyond the Grade B contours. Now they either have to ante up or get used to their DVD players...
Good definition tough-never knew what it quite meant, I thought grade B had to do with the overall picture quality.

 

[w9wi]

I never really thought about it, but does anyone have the actual definitions of what a "Grade A signal" is? Or what is a "grade B signal" is?

Do the stations or the FCC determain this? I know what I think it means, but does anyone have the "acutal definiton" Like suppose "grade a" means the signal comes in 90% of the time, or what ever?

Thanks.

I noticed some maps of TV stations also list another grade called "city grade" is this anything official?

See http://www.fcc.gov/mb/audio/bickel/curves.html.

Grade A and Grade B (and city grade) are defined in terms of the field strength predicted by the F(50,50) charts in regulation 73.699. The necessary field strength varies by channel. See regulation 73.683 for Grades A & B and 73.685 for "city grade". If the F(50,50) chart predicts a station will deliver a 75dBu signal, that means that station's signal will be at least 75dBu at least 50% of the time at at least 50% of locations.

Basically, a station must produce a signal of at least city grade strength across the entire city of license. Grades A & B are used in determining compliance with multiple-ownership regulations and cable must-carry.

Different (but similar) rules exist for digital TV. 73.622 and 73.625. There are no Grade A and Grade B contours - only "noise-limited service" and "city grade". Instead of F(50,50), F(50,90) is used - the station delivers at least x dBu at at least 50% of locations at least 90% of the time.

 

[Markxxx]

I've been reading some old books on TV broadcasting and researching old Chicago Tribune indexes and both use the terms grade A and grade B.

I wonder what the original purpose as these go back to 1951 before there was cable TV? Perhaps to make sure the TV station was covering it's city of license?

Interesting definitions though thanks for the information

 

[TexasTom]

I wonder what the original purpose as these go back to 1951 before there was cable TV? Perhaps to make sure the TV station was covering it's city of license?

To predict that quality of the coverage that stations were going to provide to viewers within their service area. Ultimately, that is the purpose of any sort of contour calculations -- even today.

 

[w9wi]

I've been reading some old books on TV broadcasting and researching old Chicago Tribune indexes and both use the terms grade A and grade B.

I wonder what the original purpose as these go back to 1951 before there was cable TV? Perhaps to make sure the TV station was covering it's city of license?

Interesting definitions though thanks for the information

Multiple-ownership. What the exact rules were at the time I'm not sure but I'd imagine it was something like if you already own Station A, you can't buy Station B if the two stations' Grade B contours overlap.

And yes, the city-grade coverage definition was to ensure the city of license was covered.

I've heard rumors of issues around that time of (AM) stations exaggerating their coverage when approaching advertising clients. Judging from the wording in the regulations I wonder if to some degree these contours were defined to provide an objective definition of coverage, so advertisers could compare apples to apples when deciding which station to pay how much for airtime?