Home |
Search |
Today's Posts |
#11
|
|||
|
|||
"Richard Clark" wrote
If all would review the standard FCC groundwave propagation curves, they would notice that they offer low AM Band signal strengths in terms of "conductivity" and that the differences in strength for the 5,000 millimhos per meter and that of 40 millimhos per meter (125 fold difference) DO NOT achieve the same proportional difference in received signal strength. In fact, the difference is so narrow you could shave with a razor as sharp as it. Even at the high end of the band the difference has to be out 700 miles to show the "conductive" ratio. Of course, over that range of transmission ONLY Sea Water would support that forecast as continental soil varies vastly in smaller spans - hence the reputation of the Sea. _______________ For a reality check, here are the approx distances to the 1 mV/m contour for 1kW of radiated power from a 90 degree vertical with a good radial ground system. The values were determined from the FCC's standard curves. Freq Conductivity/Miles 540 kHz 8/66, 40/124, 5,000/140 1,600 kHz 8/22, 40/56, 5,000/126 The average ground conductivity in the U.S. is fairly low, probably somewhere between 8 and 16 mS/m. The difference in ground wave propagation over such paths is dramatically poorer than over sea water. It is also clear from the above values how much better the low freq MW broadcast channels perform. RF |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Inverted ground plane antenna: compared with normal GP and low dipole. | Antenna | |||
Poor quality low + High TV channels? How much dB in Preamp? | Antenna | |||
QST Article: An Easy to Build, Dual-Band Collinear Antenna | Antenna |