Total posts : 196
Quote=scwis: I’m also having a bit of trouble connecting this to the impression I got from some of your earlier posts about it being impossible for a Part 15 transmitter using the stantard of a 3 meter radiator and 100 mW dc input to be received at distance because the emissions aren’t strong enough.
My previous posts haven’t stated that it was impossible for a Part 15 AM with 100 mW input power and 3-m radiator at ground level “to be received at distance.” Here is one on this topic I posted on Radio-Info on 12-31-05. I think I posted them on Part15.us, too, but this archive was easier to find and use.
These distances and fields apply to a legal Part 15 under 15.219, but they would not be legal under 15.209.
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Below are some “benchmark” values for the field strength at several distances from the r-f system described there.
These calculations are based first on a NEC-2 analysis to determine the FCC efficiency for the antenna, and then using that value with the FCC’s propagation curves for the frequency and ground conductivity, to determine the distances. This is a proven process which applies even at these low powers.
This information should assist anyone wanting to know the coverage performance of an excellent Part 15 AM r-f system, as described.
Frequency = 1700 kHz
Applied Power = 80 milliwatts (~output power of Part 15 AM tx)
Radiator = 3-meter total length including the conducting path from the tx chassis to the ground plane (antenna is ground-mounted)
Antenna System RF Resistance, Loading Coil plus Ground = 10 ohms
Ground Conductivity = 8.0 mS/m (typical value)
Radiation System FCC Efficiency = 21.12 mV/m at 1 mile for 1 kW applied
Field Strength > Distance
2 mV/m > 0.09 miles (good signal)
1 mV/m > 0.18 miles (fair)
0.5 mV/m > 0.34 miles (noisy)
0.05 mV/m > 2.5 miles (very noisy)
continued here: http://part15.us/node/683