wild949austin said:
Which is the stronger station anyway?
-105.9 has an ERP of 4500 watts, but an HAAT of 1300 ft.
-102.3 has an ERP of 26000 watts, but an HAAT of only 690ft.
So which is stronger?
In theory... 102.3, but the difference is negligible. (the local terrain will make more difference than the difference in facilities)
According to the FCC propagation curves, at a distance of 30 miles 105.9 will deliver a signal of 60.1dBu. (this is just barely strong enough to be protected from interference. In practice it'll come in just fine on most car radios but may be marginal on cheap clock radios/"Walkmen"/etc.) At the same distance, 102.3 will deliver 61.9dBu.
Would 102.3 have a stronger coverage area if its HAAT was at 1300 also?
Yes. 67.730dBu, which is a non-negligible difference but not an enormous one.
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How to work these figures for yourself:
http://www.fcc.gov/mb/audio/bickel/curves.html
- Select English units. (unless you have metric antenna height figures from the FCC website)
- Select Kilowatts (not dBk; the latter standard used to be used for television)
- Select dBu, not mV/m.
- Select FM and NTSC Television Channels 2-6.
- Select F(50,50). This means the figures you get represent what the station should deliver at 50% of locations 50% of the time. That's the standard used for determining where a station provides service. F(50,10) is for determining where a station causes interference; it returns where the station will generate an interfering signal at 50% of locations 10% of the time. F(50,90) is for digital television, where a less-than-good signal doesn't result in a snowy picture, it results in no picture at all.
- Select Field Strength.
- Click "Submit Choices".
(A second page comes up with three boxes)
- Input the Effective Radiated Power in kilowatts. (not watts. For 102.3, input 26, not 26,000.)
- Input the antenna Height Above Average Terrain in feet. (unless you selected metric)
- Input the distance at which you want to find the signal strength. This is somewhat arbitrary for comparing two stations. IMHO 30 miles is a reasonable figure for comparing stations of Class C2 or higher. (both of the stations cited in this thread are C2)
DISCLAIMERS...
- Again, you're getting a F(50,50) figure. When I say 105.9 is predicted to deliver 60.1dBu at 30 miles, that means at half of locations 30 miles from the tower, half the time, the 105.9 signal will be 60.1dBu or more. Half the time, it will be *weaker* than 60.1dBu, and at any given time it will be weaker than 60.1dbu at half of locations at 30 miles.
- The number assumes a receiving antenna at 30 feet. Obviously, nobody uses an antenna 30 feet high on their FM radio! (so don't get out a field strength meter & expect to read 60.1dBu 30 miles from the 105.9 transmitter -- unless you have a 30-foot pole for the antenna...)
- Terrain will have MAJOR effects on the received signal. It will have differential effects on the signals of these two stations, both because their antennas are at different heights and because they're at different locations. Do not assume that 102.3 will be 1.8dB stronger than 105.9
everywhere; there will be many locations where the difference is more dramatic -- and many at which 105.9 is stronger than 102.3.
