Why Do Some FM Stations Have Different Horizontal and Vertical Power?

[Gregg.]

I see this occasionally. Most FM stations broadcast at a certain "effective radiated power." But sometimes they have two different powers. For instance, 89.7 WDVR in Delaware Twp. NJ is powered at 3,800 watts vertical but only 6 watts horizontal.

WDVR-FM 89.7 MHz - Delaware Township, NJ

Radio Station Information for WDVR 89.7 MHz FM, Delaware Township, NJ

radio-locator.com

I also notice some FM stations have regular power, along with another, higher peak power. For instance, CFMI Vancouver is 53,000 watts ERP, but 100,000 watts peak or maximum power.

https://fccdata.org/?lang=en&canfm=CFMI-FM

 

[RF101]

CFMI, like most of the Mt Seymour stations, is highly directional. This reduces multipath reflections off the backsides . CFMI uses a three-side panel array I think.

If you look up the FCCDATA.org Canadian-based listing you will find measurements in five-degree increments. CFMI peaks at 100kw ERP at 265 degrees. Its minimum is -38.68 dB at 25 degrees... less than 100 watts ERP.... in the direction of the mountainside. If you average out the power values you should arrive at 53 kw ERP.

https://fccdata.org/?lang=en&canfm=CFMI-FM

The different H/V values in the US may be EMI exposure issues , power considerations, compatibility with other tower tenants, windload/icing factors , etc. Each case is unique.

 

[davideduardo]

The unequal vertical and horizontal powers I am most familiar with are older installations where the vertical and horizontal antennas are separate, rather than "circular" or combined V and H bays.

 

[PTBoardOp93]

WDVR is a good case to point out. I think many FMs at the low end of the dial ended up with higher vertical power as a way to meet contour spacing requirements from a TV channel 6. In WDVR's case, that would be WPVI.

Refer to 47 CFR 73.207 (c), which was amended several times through the 80s and 90s, probably in response to demand for NCE channels from religious interests. One of the old timers might remember better than me.

 

[Dr. Bob]

WDVR is a good case to point out. I think many FMs at the low end of the dial ended up with higher vertical power as a way to meet contour spacing requirements from a TV channel 6. In WDVR's case, that would be WPVI.

Refer to 47 CFR 73.207 (c), which was amended several times through the 80s and 90s, probably in response to demand for NCE channels from religious interests. One of the old timers might remember better than me.

Yes the channel 6 protection requirements is one as is grandfathered “super powered“ stations that were required by the FCC to keep vertical power at the maximum in the current rules when they implemented it but were allowed to retain their previously licensed power in the horizontal plane which was above the maximum permitted currently. An example is WLFP (ex-WMC-FM) in Memphis. Their license specifies 300 kW in the horizontal plane but only 100 kW in the vertical plane.

 

[boiseengineer]

Was told that the reason several Eugene OR stations have a different h & v powers is an engineer insisted it would perform better with lower vertical ERP.
KZEL started out in '62 with 70 kw ERP h&v.
A few changes in power & HAAT until they ran 100 kw ERP h&v into the 80's.
Around '89 they changed antenna and dropped the vertical power to 43 kw ERP (100 kw h).

 

[SomeRadioGuy]

this one used to have 1 watt because of then analog channel 6

WPEB-FM 88.1 MHz - Philadelphia, PA

Radio Station Information for WPEB 88.1 MHz FM, Philadelphia, PA

radio-locator.com