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Question about VHF

D

dustintv

I've got a question about VHF...

Is 7(Chs. 2,4,5,7,9,11,13) the most VHF stations you can have for a city?

Also, I've noticed that when a city has two VHF channels next to each other, it's usually channels 4 and 5(NY, LA, DC, Seattle, Albuquerque etc.) or channels 6 and 7(Denver, Omaha, Boise etc.) Why is that? Why don't you ever see Channels 5 and 6 or channels 9 and 10?

Sorry if it sounds dumb, but I'm just curious.
 
> I've got a question about VHF...
>
> Is 7(Chs. 2,4,5,7,9,11,13) the most VHF stations you can
> have for a city?
>
> Also, I've noticed that when a city has two VHF channels
> next to each other, it's usually channels 4 and 5(NY, LA,
> DC, Seattle, Albuquerque etc.) or channels 6 and 7(Denver,
> Omaha, Boise etc.) Why is that? Why don't you ever see
> Channels 5 and 6 or channels 9 and 10?
>
> Sorry if it sounds dumb, but I'm just curious.

There are gaps between Channels 4 (66-72 MHz) & 5 (76-82 MHz), and between 6 (82-88 MHz) & 7 (174-180 MHz). Since they're not adjacent channels, they can be located in the same city without interference.

Channels 9 (186-192 MHz) and 10 (192-198 MHz) are adjacent so if they were in the same city with full 316 kW transmitters, they'd bleed all over each other. This doesn't affect cable because the incoming signals are much lower than with over-the-air signals in a local area.
 
> > I've got a question about VHF...
> >
> > Is 7(Chs. 2,4,5,7,9,11,13) the most VHF stations you can
> > have for a city?
> >
> > Also, I've noticed that when a city has two VHF channels
> > next to each other, it's usually channels 4 and 5(NY, LA,
> > DC, Seattle, Albuquerque etc.) or channels 6 and 7(Denver,
>
> > Omaha, Boise etc.) Why is that? Why don't you ever see
> > Channels 5 and 6 or channels 9 and 10?
> >
> > Sorry if it sounds dumb, but I'm just curious.
>
> There are gaps between Channels 4 (66-72 MHz) & 5 (76-82
> MHz), and between 6 (82-88 MHz) & 7 (174-180 MHz). Since
> they're not adjacent channels, they can be located in the
> same city without interference.
>
> Channels 9 (186-192 MHz) and 10 (192-198 MHz) are adjacent
> so if they were in the same city with full 316 kW
> transmitters, they'd bleed all over each other. This
> doesn't affect cable because the incoming signals are much
> lower than with over-the-air signals in a local area.
>
How far apart to adjacent stations have to be before they don't bleed. I noticed when I was in Kankakee I could get Channel 2 (Chicago) and Channel 3 (Champaign) consitantly without any bleed.

And when I lived in Arlington Heights (NW Suburbs of Chgo) I could get Channel 7, 9 (Chicago) and Channel 8 (Grand Rapids, MI) without any bleed. I got channel 8 in the summer. <P ID="signature">______________
Once I figured out the meaning of life....Then I forgot to write it down.</P>
 
> How far apart to adjacent stations have to be before they
> don't bleed.

Primarily, it has to do with the predicted signal strength coverage. There is a service contour table for low-VHF, high-VHF, and UHF at the FCC website:

<a target="_blank" href=http://www.fcc.gov/mb/audio/bickel/curves.html>http://www.fcc.gov/mb/audio/bickel/curves.html</a>

Every station has a grade-B, grade-A, and city-grade contour on the official map filed in their application to the FCC. The actual contour is plotted based on effective radiated power, terrain, etc.

Adjacent channel stations cannot have any overlap in their grade-B contours (coverage area). There are additional separation rules that apply to UHF, having to do with harmonics, but if I tried to explain that, your eyes would glaze over.<P ID="signature">______________


</P>
 
> > How far apart to adjacent stations have to be before they
> > don't bleed.
>
> Primarily, it has to do with the predicted signal strength
> coverage. There is a service contour table for low-VHF,
> high-VHF, and UHF at the FCC website:
>
> http://www.fcc.gov/mb/audio/bickel/curves.html
>
> Every station has a grade-B, grade-A, and city-grade contour
> on the official map filed in their application to the FCC.
> The actual contour is plotted based on effective radiated
> power, terrain, etc.
>
> Adjacent channel stations cannot have any overlap in their
> grade-B contours (coverage area). There are additional
> separation rules that apply to UHF, having to do with
> harmonics, but if I tried to explain that, your eyes would
> glaze over.
>
To use one example, Salisbury, NC, is about 45 miles from
Greensboro and 45 from Charlotte. Both WFMY/2 Greensboro and
WBTV/3 Charlotte can be picked up there, although I'm told
WBTV's picture is not the best, owing more to their transmitter
site west of Charlotte than anything else. Likewise, WGHP/8
High Point and WSOC/9 Charlotte can also be picked up there.

When I lived just outside Winston-Salem in the early '80s
I got WGHP and WDBJ/7 Roanoke, VA (about 100 miles from
where I lived) with absolutely no interference problem.

I've also known people living just outside Athens, GA, who
could get WYFF/4 Greenville, SC, and WAGA/5 Atlanta. Athens
is 65 miles from Atlanta, 90 from Greenville (approximately),
and both came in OTA with no problem.
 
I was just thinking about the situation in Salisbury NC. That city is about 35 miles from both the channel 8 and channel 9 Txs. Channel 2 is also about 35 miles, while 3 is about 50 miles. I'm of the opinion that all 4 channels put a grade B signal into the area. All are full power non directional and 2 and three have 1800 plus foot towers. 8 and 9 towers are more like 1400. All 4 stations can easily be recieved with "rabbit ears," 3 not as well as the others. Obviously, the grade B contures of adjacent channels can overlap by quite a bit, with no problem. Actually, Salisbury is almost OTA TV nirvana, with the ability to recieve about 10 channels very clearly from each market.
 
Re: Question about adjacent channel stations

> Adjacent channel stations cannot have any overlap in their
> grade-B contours (coverage area).

Are you sure you're not talking about co-channel stations instead of adjacent channel? Phoenix and Tucson have several adjacent channel stations and their grade-B contours have significant overlap. FCC regs require adjacent channel stations to be 59.5 miles separated if VHF and 54.5 miles if UHF - that's well within grade-B contours.
 
Re: Question about adjacent channel stations

> > Adjacent channel stations cannot have any overlap in their
>
> > grade-B contours (coverage area).
>
> Are you sure you're not talking about co-channel stations
> instead of adjacent channel? Phoenix and Tucson have
> several adjacent channel stations and their grade-B contours
> have significant overlap. FCC regs require adjacent channel
> stations to be 59.5 miles separated if VHF and 54.5 miles if
> UHF - that's well within grade-B contours.

That's what I meant. Thanks for the correction and catching my misspeak.<P ID="signature">______________


</P>
 
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