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..just bought a 50kw station and noticed that the tower is only 430 feet and that i can presummably go to 499 feet HAAT....how much farther range can i get the signal with an increase of 69 feet? Would it be worth my while?
I hope someone can help me out here!
Thanks
I'm making the assumption that this is an FM station.
Is the tower height actually 430' or is this the licensed antenna height?
What is the tower's HAAT?
Most likely, the additional 69' won't make a significant difference in coverage.
Assuming that your post applies to an FM station, here are some numbers based on the FCC f(50,50) FM curves for flat terrain, and a 6-bay, 1-wave spaced antenna radiating 50 kW at 98 MHz:
The radiation center of the present antenna system is ~400 ft HAAT. The radius of the 1 mV/m contour is 30 miles, and the area within that contour is 2,827 square miles.
If the antenna radiation center was located at the maximum height of 492 feet HAAT, the 1 mV/m contour radius will be 32.4 miles, and the area within it will be 3,298 square miles.
Note that this is a height increase of 92 feet for the antenna radiation center, and not the 69 feet you mentioned. But the FCC licenses FM stations on the height of the antenna radiation center, not on the height of the tower supporting the antenna.
So for these assumptions the 1 mV/m radius will increase by 8%, and the coverage area within it would increase by 16.7%.
For only a few extra miles of coverage, it probably won't be worth the expense unless you are a rimshot into a big city. Maybe you could move it up to the very top of the current tower cheaply.
If you're basing your question purely on the definition of a Class-B, know that your antenna can be as high as you can afford to place it. ERP is calculated based on whatever HAAT you end up at, antenna gain, and the transmission line loss; the higher you go, the lower the ERP will be (generally speaking). Also, is the base of that tower at 0' HAAT? Or is there an offset? I'm moving sites this summer - the base of the new site is 100' HAAT.
-D
ERP is calculated based on whatever HAAT you end up at, antenna gain, and the transmission line loss; the higher you go, the lower the ERP will be (generally speaking).
However the reduction in ERP will be that which produces the same distance to the 1 mV/m contour as if the station ran the maximum ERP from the HAAT limit for that power and Class of FM station.
So the area within the 1 mV/m contour will be the same for an "overheight" system, but the field strengths within that area can be somewhat reduced.
It's preferable to have more height than power, but if your HAAT is lower than the maximum HAAT which allows 50kw, you're not getting maximum coverage. Signal strength will go up 6 dB every time your height is doubled if power is constant.
What's holding the tower at 399'? If you increase the height, try for 500 feet.
If you're basing your question purely on the definition of a Class-B, know that your antenna can be as high as you can afford to place it. ERP is calculated based on whatever HAAT you end up at, antenna gain, and the transmission line loss; the higher you go, the lower the ERP will be (generally speaking). Also, is the base of that tower at 0' HAAT? Or is there an offset? I'm moving sites this summer - the base of the new site is 100' HAAT.
-D
Go to FCC.gov then media ( on the right side), then FM Query (left side in media) see what your HAAT is.
Another tool lets you know where you can move based on existing stations.
If you are a rimshot look at the ERI website for pattern studies. A pattern study can yield 6db of gain. (double power plus double power). Some times 9 or 12.
Old owner wanted a better signal in a small town or in another part of the coverage area. Placement of the antenna has a null over the town you want to cover with as much as a 9 db null. I have seen this so many times. Turning the antenna made a station worth double on day one....
ERP is calculated based on whatever HAAT you end up at, antenna gain, and the transmission line loss; the higher you go, the lower the ERP will be (generally speaking).
However the reduction in ERP will be that which produces the same distance to the 1 mV/m contour as if the station ran the maximum ERP from the HAAT limit for that power and Class of FM station.
So the area within the 1 mV/m contour will be the same for an "overheight" system, but the field strengths within that area can be somewhat reduced.
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