Mr. Rich: Could/Would you model a ground mounted transmitter operating at 1710 kHz running an input power of 100 mW driving a 3 meter monopole. I am curious as to what the predicted field strength would be at various distances.
Thanks, Mr. Druid.
From a post on Part15us some time ago:
Below are some calculations of groundwave field strength at several distances from the r-f system described there.
These calculations are based first on a NEC 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.
DATA:
Frequency = 1700 kHz
Applied Power = 80 milliwatts (r-f output power at input to loading coil)
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)
RESULTS:
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*)
* based on use of a good AM receive system and lack of r-f noise/interference at the receive location
Thanks. 1700 is close enough.
that is one of the reasons it is preferred by low power broadcasters. so "fair" might move from the 1mV slot to 0.5mV "Noisy" slot because of the lower noise floor and the better matching of the 3m loaded whip antenna to the frequency (in this case 1710) used.
Rich, on the compliant 3 metre antenna+ground lead limit, if it were possible to mount the tx at any point in a 3m ground mounted antenna, would the optimum transmitter insertion point be half way up, or at the very top, for maximum radiated signal ?
Reason i ask is that you stated some time ago that if the tx point is inserted half way up the antenna, the current between the tx and ground, is linear ?
Thanks,
Paul.
that is one of the reasons it is preferred by low power broadcasters. so "fair" might move from the 1mV slot to 0.5mV "Noisy" slot because of the lower noise floor and the better matching of the 3m loaded whip antenna to the frequency (in this case 1710) used.
However the maximum field intensity permitted just 30 meters away from a compliant Part 15 AM system operating on 1710 kHz is only ~6% of 0.5 mV/m.
... if it were possible to mount the tx at any point in a 3m ground mounted antenna, would the optimum transmitter insertion point be half way up, or at the very top, for maximum radiated signal ?
Moving the feedpoint higher up on a 3-meter Part 15 AM radiator with its base at r-f ground is a trade-off between the extra radiation from the linear current along the bottom section, the extra loss due to the higher inductance loading coil needed to resonate that configuration, the reduced r-f system bandwidth, and the added difficulty of tuning and maintaining the resonance of the antenna system.
Rich,
Thanks for the information.
After previously posting, it did later enter my mind about bandwidth, reason being if the feedpoint was very near the top, it would not tune up without some radiator above the feedpoint, and if it were 12", it would have exceptionally narrow bandwidth !
Looks like base loading the 3m section is the way to go then.
Paul.
Rich, Thanks for the information. ...
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Thanks for your thanks :<)