Here is a chart estimating the frequency to be used to communicate with another station at a given distance.
4MHZ Good choice for communications up to approximately 200 miles throughout the day. Longer range communications may be possible in late afternoon. Short range communications (up to 200 Miles) should slowly deteriorate but may continue through the night.
6MHZ Good choice for long range communications around midnight. A ship off the coast of New York should easily be able to contact any coastal radio station in the continental US.
8 MHZ This band offers shorter propagation during the day and conditions conducive to long range propagation conditions at night.
12 MHZ Late afternoon and evening hours offer maximum long range communications. Communications between stations less than 100 miles may be possible in the early morning hours.
16 MHZ Late afternoon and evening hours offer maximum long range communications. Communications over "short" distances (500 miles) are possible throughout the day but should gradually deteriorate and become impossible on
this frequency at niqht.
22 MHZ
During period of high solar activity, this band can support worldwide communications with relative low power transmitters.
