NavList:

This type of equipment is good for a very long distance mainly determined by the power of the transmitting station. For enroute navigation, airways, like "highways in the sky" were created with radio transmitters placed on the ground at each end of each leg of the airway. The signals have to be strong enough so that you can receive them at the halfway point of each airway leg. You track outbound from one station until halfway to the next station then start following the signal to the second station. As an example, a route I flew many times was  "A17" from Bimini, Bahamas to Puerto Rico. You take off from Miami or Ft. Lauderdale and tune in the radio station on Bimini which transmits on 396 kcs with a Morse code  identification of "ZBB." You use the radio direction finder to head for Bimini which is 55 NM from Ft. Lauderdale. After passing over Bimini you turn to a heading of 121º magnetic and track outbound until halfway to the next radio station located on the island of Grand Turk at the very southeast end of the Bahamas chain. Grand Turk transmits on a freq. of  232 kcs with the ident of "GT." After passing GT the next station is located on the north shore of Puerto Rico about 60 miles west of San Juan transmitting on the frequency of 391 kcs, ident "DDP." Now here is the important part, the leg from ZBB to GT is 516 NM (593 miles). This means that you can receive the signal 258 NM at least from each station. It is reasonable to believe that had AE's radio direction finder been working she would have been able to hear Itasca at a similar distance. This is born out by the fact that Itasca heard AE's much less powerful transmitter several hundred NM out.