Polarization: FM & Television

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#1
Need some good backrounder on antenna and broadcast polarization.

Like...

What do most FM broadcasters use? And what percentage of stations use vertical, horizontal, both or other?

Furthermore, do individual stations change the relative power to their vertical and horizontal antenna elements at different times of the day, like rush hour vs night time?

Is there a handy website to find out information about local FM broadcasters practices with regards to polarization?

Thanks.

I know that all television broadasts are horizontal polarization.
 

FOX TV

Contributor
#3
Transmit polarity

Need some good backrounder on antenna and broadcast polarization.

Like...

What do most FM broadcasters use? And what percentage of stations use vertical, horizontal, both or other?

Furthermore, do individual stations change the relative power to their vertical and horizontal antenna elements at different times of the day, like rush hour vs night time?

Is there a handy website to find out information about local FM broadcasters practices with regards to polarization?

Thanks.

I know that all television broadasts are horizontal polarization.
Virtually all FM is either circular or dual polarity because they hope to program to vehicle antennas (Vertical) and home antennas (Horizontal).
Dual polarity requires twice the transmitter power for FM, and circular requires more transmitter power as well, but not quite as much as dual polarity, and of course, broadcasters want to avoid running more power than needed due to power costs.

Polarity of TV antennas is normally horizontal, but circular polarity is sometimes used, but this requires more transmitter power as well. Circular polarization for TV is normally used in problematic or difficult reception areas where mountains and other objects can alter the polarity by reflection or refraction.

Horizontal polarity has less atmospheric noise due to the fact that most natural and man made noise is usually vertically polarized, thus there is less natural horizontally polarized noise to deal with.

The power levels for digital TV is always the same. You are required to run 90 to 100% of your assigned power levels at all times. Besides that, who is going to mount a vertically polarized antenna for channel 2 or 3 VHF. It would be as tall as a tower. LOL.
 
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#4
Just a note, as far as I've been able to find out all channels from 6 and below have been removed from the TV service. That means Ch 7 is the lowest at a frequency. Ch 7: 174 - 180 MHz which is shorter than the 2meter ham band at 140-150MHz so that's less than a half meter for a quarter wave or about 18" not at all bad for vertical antenna if TV used vertical. Ch 2, the lowest was 54 - 60MHz 54 MHz is about 5.5 meters and a quarter of that is approximately (5.5*39.37)/4 ~ 54 inches or about 4.5 feet hardly the size of a tower.
 
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MrPogi

Moderator, , Webmaster of Cache Free TV
Staff member
#5
Just a note, as far as I've been able to find out all channels from 6 and below have been removed from the TV service. That means Ch 7 is the lowest at a frequency.
Wrong answer. Channels 2-6 are still in use. Most broadcasters have chosen not to use these channels due to problems with noise and multi-path in this part of the spectrum.

This list is dated - but these are the full-power stations broadcasting on channels 2-6 as of 2009. This list doesn't include LP (low power) stations...

STATE - DMA - Call Sign - Network - Channel

PA PHILADELPHIA WPVI ABC 6
AZ PHOENIX KNAZ NBC 2
FL MIAMI WSBS ind 3
CT HARTFORD WEDY PBS 6
TN NASHVILLE WTVF CBS 5
NV LASVEGAS KVNV NBC 3
TX SANANTONIO KCWX CW 5
MI GRANDRAPIDS WGVK PBS 5
NV LASVEGAS KVBC NBC 2
TN MEMPHIS WMC NBC 5
NY ALBANY WRGB CBS 6
KY LEXINGTON WDKY FOX 4
VA ROANOKE WBRA PBS 3
KS WICHITA KBSD CBS 6
IA DESMOINES WOI ABC 5
OH TOLEDO WLMB fam 5
VA TRI-CITIES WCYB NBC 5
IL QUADCITIES WHBF CBS 4
NE LINCOLN KHAS NBC 5
SD SIOUXFALLS KDLO CBS 3
GA AUGUSTA WCES PBS 6
OR MEDFORD KOBI NBC 5
GA ALBANY WABW PBS 6
AK ANCHORAGE KYUK PBS 3
AK ANCHORAGE KYES MyN 5
ME BANGOR WLBZ NBC 2
WY IDAHOFALLS KJWY NBC 2
WV CLARKSBURG WDTV CBS 5
MT BILLINGS KYUS NBC 3
SD RAPIDCITY KOTA ABC 2
MI MARQUETTE WBKP CW 5
CO GRANDJUNCTION KREX CBS 2
MT BUTTE KXLF CBS 5
MT BUTTE KTVM NBC 6
CA EUREKA KIEM NBC 3
WY CASPER KPTW PBS 6
NE NORTHPLATTE KNOP NBC 2
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#7
Rickie,

Here's some history in a nut shell. After World War 2, the electronic manufactures instantly lost their primary purchaser (Uncle Sam). They all looked for a new civilian market and making television happen was the obvious answer. Low-band VHF was where it all started but the new 'TV-Band" wasn't empty. There is (still) a 2 mHz gap between channels 4 and 5 that was meant for Air Traffic Control. What it really meant, was less interference from an adjacent competing TV channel on the crappy TV tuners of the day. Channels 4 and 5 were both PRIME real estate!

I must add that Seattle had both (analog) channels 4 and 5 as well as strange noises and pulsed screens, whenever I tuned between the two channels.

Jim

EDIT: Here's a link to the Airport system: http://en.wikipedia.org/wiki/Marker_beacon
 
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