Class A FM Question

[bwilliam614]

Two Class A's here in Columbus, Ohio.

1.2600 watts/505 feet ground

2.1900 watts/413 feet off ground

I was just curious if anyone knew roughly how many more feet the second station could raise their antenna off of the ground without breaking the Class A rule of 328 feet/6000 watts? Or, if they bought a new antenna, and kept the height at 413 feet, what's roughly the most powerful antenna they could buy without breaking the Class A rule?

 

[local oscillator]

Your first example is equivalent to 6 kW at 328' HAAT. Your second example is equivalent to 3 kW at 328' HAAT. I have to assume that #2 is a "3 kW Class A," is operating at maximum facilities, and has those facilities because it doesn't meet the requirements for a "6 kW Class A." See FCC Rules Part 73.213: http://louise.hallikainen.org/FCC/FccRules/2012/73/213/.

 

[ChiefEngineer]

Not all Class A 3 KW stations upgraded, or could. It depends on their interference to other stations also. A study should be run to determine if an upgrade is possible.

 

[Schroedingers Cat]

The other thing you ned to know, in general, in cases like this, is whether the facility was authorized under Section 73.215. Many stations are using the highest nondirectional power they can use, not the reduced ERP specific to the HAAT. That is often advantageous, because the average power (Canada specifies this in their records), is often the same or sometimes higher than the directional antenna average power would be, particularly for the actual directional pattern of the final antenna design, as opposed to the licensed maximum pattern relative field (and hence power) in each direction ususally specified. Also, you can mount the nondirectional antenna without regard to parasitic effects of tower mounting, and don't need a surveyor to find true north.

 

[bossbill]

"feet off ground" is not the criterion. It's HAAT - height above average terrain, and may be different for two stations at separate locations, even if height above ground level is the same.

 

[markbohach]

"feet off ground" is not the criterion. It's HAAT - height above average terrain, and may be different for two stations at separate locations, even if height above ground level is the same.

Bill is correct. HAAT (height above average terrain) can vary greatly from site to site- even if they are separated by only a few miles.. The WBNS Tower actually sits below average terrain at ground level. This is why you see towers on big hills wherever possible. It's far easier and cheaper to put up a 200 ft tower on a hill and use the natural terrain advantage than install a 600 ft tower in the flatland and have to paint and light it.

Mark Bohach