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modulation does not matter for range. however FM requires a greater signal strength to convey the information. if you are trying for distance, AM works with less recovered signal.

exclusive of digital modes, the most distance effective signal is CW. unmodulated signal, on or off.

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FM uses 10 times the bandwidth and conveys more audio frequency range within it's signal than an AM one. FM has the benefit that building antenna gain is relatively easy so the Total Power Output of FM transmitters is often lower than for AM transmitters. You can generally expect to get 100kW Effective Radiated Power with only 20kW of input.

AM uses a significantly lower frequency and ground wave propagation is much more likely which gives AM the benefit of being able to reach "over the horizon" where FM simply cannot.

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