Lower frequency vs Higher frequency on the AM band
Hello,
Does anyone can give me a typical field strength for 3-meter antenna based on the 2 following information:
1) Transmitter set to [b:bd68a5a22e]540[/b:bd68a5a22e] kHz with a loading coil inductance of [b:bd68a5a22e]2567.70 [/b:bd68a5a22e]uH
2) Transmitter set to [b:bd68a5a22e]1580[/b:bd68a5a22e] kHz with a loading coil inductance of [b:bd68a5a22e]299.03 [/b:bd68a5a22e]uH
I am still wondering if i can achieve the maximum coverage if i broadcast on lower frequency (< 600 kHz) rather than higher frequency (> 1500 kHz). It appears that radiowaves on the lower frequency will travel easily in the buildings and houses. Anyone can comment this?
Also, i haven't still experiment to broadcasting in the lower frequency, but due of the loading coil inductance, i suspect that the Q factor will be such very high than the Q factor at the higher frequency.
I would like to see some comments about that before i will go to build my loading-coil made myself for the lower frequency (which takes almost a day of work).
Regards
Yves Roy
Hi,
I wish I could give you real data or experience about this. All I offer is that you should try it and see how it compares to the higher frequencies.
You don't need field strength measurements. Just drive around and see which gives the best long range signal.
If you do, your experience will be a valuable report to this board.
Neil
I am still wondering if i can achieve the maximum coverage if i broadcast on lower frequency (< 600 kHz) rather than higher frequency (> 1500 kHz). It appears that radiowaves on the lower frequency will travel easily in the buildings and houses. Anyone can comment this?
The real benefit of the lower freqs is that their groundwave propagation losses are lower. However that difference doesn't amount to very much for the short paths possible from Part 15 AM systems.
Also, i haven't still experiment to broadcasting in the lower frequency, but due of the loading coil inductance, i suspect that the Q factor will be such very high than the Q factor at the higher frequency.
Forgetting Q factor, 3-meter radiators on 600 kHz have roughly 1/10 the radiation resistance value as 3-meter radiators on 1.7 MHz. So even if you could match into each of them with the same total of 30 ohms of ground and coil losses, the radiation efficiency of the 600 kHz system would be reduced by 90% from the system on 1.7 MHz.
So the two realities above favor the use of the highest possible frequency for Part 15 AM.
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