Is having both vertical and horizontal polarization or circular polarization still mandated by the FCC for FM Broadcast?

[pclover]

So I’ve heard in the past that the FCC mandates that you have both vertical and horizontal polarization for FM Broadcasts.

Typically, most high power stations use circular polarization that solves this problem. However, it appears there’s a few high power stations that are vertical only?

Perhaps somebody here better knows what the rules are now today.

 

[Radio Bob]

I believe that Horizontal only is the only polarization the commission requires for FM with one exception. At the low end of the dial around 88.1 some stations were allowed to go vertical only to prevent interference with TV channel 6 which broadcasts horizontally. Once given permission to broadcast vertical only if that station then wanted to move up the dial to a higher frequency they could continue with vertical only. Of course you can get approval for circular polarization at any time.

 

[PTBoardOp93]

So I’ve heard in the past that the FCC mandates that you have both vertical and horizontal polarization for FM Broadcasts.

No. 47 CFR 73.316 says:

It shall be standard to employ horizontal polarization; however, circular or elliptical polarization may be employed if desired. Clockwise or counterclockwise rotation may be used. The supplemental vertically polarized effective radiated power required for circular or elliptical polarization shall in no event exceed the effective radiated power authorized.

Emphasis is mine.

 

[secondchoice]

IIRC there use to be a couple of commercial stations (class B or C) that had different horizontal and vertical power. I can't remember calls or COLs It was over 40 years ago! Would it have been some kind of IF or harmonic issue with an old VHF TV station that would cause the commission to limit one polarization but not the other?

I believe most Class A, B, or C commercial FM stations pre 80 / 90 were at least horizontal polarized. There were a bunch of FMs (now B or C) that had 8 or more horizontal bays for big time gain. No need to send power above the horizon. The smallest number of bays of any FM station I ever worked at was 4 bays. It was Class A 3kw horizontal only. Back before FM listership approached AM levels (1980ish or latered) power bills, and labor (lots of automation systems) were an issue. Tube FM transmitters 40 & 50 years ago were not as efficient as today's equipment.

Rule of thumb (not scientific) dependable FM reception is a line of sight plus one third at best. Your mileage may vary depending on terrain and if you're directional. As for antenna polarization, circular's performance seems to work "almost" as well as dual polarized with a better power bill.

 

[davideduardo]

Rule of thumb (not scientific) dependable FM reception is a line of sight plus one third at best. Your mileage may vary depending on terrain and if you're directional. As for antenna polarization, circular's performance seems to work "almost" as well as dual polarized with a better power bill.

I built the first FM in Ecuador, which was also the first in northern South America.

Because there were few regulations, there was no requirement for polarization. So we experimented with different arrays in both horizontal and vertical modes. We made the antennas in our own shop out of plumbing copper and aluminum tubing and fittings, so we could try varying combinations of elements and polarization.

Our first FM was in Quito, at around 10,000 feet AMSL and in very irregular hilly and mountainous terrain. We found, after lots of efforts, that only vertical polarization worked the best and built all our other FMs (5 in Quito alone) with pure vertical elements. When we took our "premier" FM up 3000 feet above the city, we also used only vertical and considerable beam tilt (using a motorcycle chains and a hand crank to adjust).

It worked. By the later 60's. HCTM 95.1 was #2 in upper income listening, only beaten by my HCRM 570, a Top 40 station.

 

[RadioFan2J3]

IIRC there use to be a couple of commercial stations (class B or C) that had different horizontal and vertical power. I can't remember calls or COLs It was over 40 years ago!

WBBQ-FM, Augusta, was one of those stations. 100kW ERP horizontal, 37kW ERP, vertical.

I remember many station promos where the power was 137kW.

 

[KenoGuy]

WWDV 96.9 Zion, IL is 50,000 Watts horizontal, 38,000 Watts vertical. IIRC this (and a directional antenna) was done to reduce interference to short spaced co-channel (and co-owned) WDRV 97.1 Chicago. WWDV's tower is about a mile north of the WI/IL border in Kenosha County.

BTW, they simulcast programming as The Drive.

 

[The New Chico]

WNCI Columbus OH is a grandfathered super power FM, 175kW H and 105kW V. Directional, somewhat.

 

[secondchoice]

WNCI Columbus OH is a grandfathered super power FM, 175kW H and 105kW V. Directional, somewhat.

That's a lot of power for only a 591 foot above average terrain height in class B territory. Was the directional to protect someone? To be "grandfathered", that would have to be a really really old license. One would think they could have found a "clean" channel. There weren't a bunch of FM stations back then.

 

[Radio Bob]

That's a lot of power for only a 591 foot above average terrain height in class B territory. Was the directional to protect someone? To be "grandfathered", that would have to be a really really old license. One would think they could have found a "clean" channel. There weren't a bunch of FM stations back then.

I believe they went to that height because they were owned by Nationwide Insurance who had just built a new building in downtown Columbus and they could locate atop it.