Richard Black, aboard the Itasca, then forwarded a message at 2230 GMT, June 23rd, to Earhart at Darwin or Bandoeng, Indonesia, providing information regarding radio reception:

Ontario NIDX transmitter 500watts, frequency range 195 to 600 kHz, either CW or MCW. No high frequency equipment on board. Swan, NIJP, can transmit 0.5kwatts between 195 and 600 kHz, and between 2000 and 3000 kHz. Also can transmit 100 watts 600 to 1500 kHz and from 3000 to 9050 kHz. 35 watts voice available 350 to 1500 kHz and 3000 to 9059 kHz. Please confirm and designate signals desired from Ontario, Itasca, and Swan within these ranges best suited to your homing device. Itasca can give any frequency desired.⁴

The Itasca sent another message to Earhart at 0120 GMT, June 24th, stating that they wished 12 hours prior notice of departure from New Guinea, and “… full information regarding your desires in matter of radio frequencies and communication schedule. We will conform to any frequencies desired; important anticipate your departure as communication via Port Darwin very slow. Itasca on station Howland Island at 2200 this evening. This vessel will contact Swan and Ontario and advice them fully.”⁵

On June 25th at 2245GMT, the Coast Guard San Francisco office sent a radio message:

... Mr. Putnam now at Oakland and advises Ms. Earhart at Bandoeng Java for repairs to motors and departure indefinite. She will cable details communications from Port Darwin direct San Francisco and you will be given all information immediately. All communications from plane will be on 500, 3105, or 6210 kHz by voice, positions being given at 15 and 45 minutes past the hour. Itasca adjust transmitter for possible use 3105 kHz for voice. Direction finder on plane covers range of about 200 to 1400 kHz.⁶

At 0720GMT, June 26th, Earhart responded with:

Suggest Ontario standby on 400 kHz to transmit letter N 5 minutes on request with station call letter repeated twice end every minute. Swan transmit voice 9000 kHz or if I unable receive be ready on 900 kHz. Itasca transmit letter A, position, own call letters, as above on half hour at 7.5 MHz. Position ships and our leaving will determine broadcast times specifically. If frequencies mentioned unsuitable night work inform me at Lae. I will give long call by voice 3105 kHz quarter after hour, possible quarter to.⁷

There has been a lot of speculation about these instructions, but it appears that the advice for Ontario is appropriate for radio bearing work. The Swan high frequency is suitable for voice reception by Earhart, as is the 900 kHz frequency. It is unclear why Earhart wants the Itasca to broadcast at 7500 kHz, since she is asking for code and cannot use that frequency for direction finding. The actual wording in the telegram is 7.5 megacycles.

At 1930GMT, June 26th, the San Francisco office of the USCG sent out a priority radio message stating:

Following information from Earhart this date quote homing device covers from 200 to 1500 and 2400 to 4800 kHz any frequencies not repeat not near ends of bands suitable unquote. … assume continuous signals after her direction finder in range. See broadcast on quarter after and quarter before hour on 6210 and 3105 kHz. Am advising Earhart that Itasca will voice radio her on 3105 on hour and half hour as she approaches Howland. Repairs made and Earhart now at Sourabaya expects leave dawn this date for Part Darwin and next day for Lae. Advice priority if adjustments Tare ten transmitter satisfactory for use on 3105.⁸

Here, the CG office is interfering in setting up communication protocols between Earhart and Itasca by stating that the Itasca will voice call her on 3105 kHz on the hour and half hour. There is no contemporaneous documentation to verify that the information regarding the double frequency band of Earhart's RDF came from Earhart or George Putnam. Based upon the quoted passage, it should be taken at face value and accepted as coming from Earhart.

At 0435GMT June 27th, the Itasca complained that the San Francisco CG office was interfering with its ability to set up communications with Earhart, and suggested that Itasca be provided complete independence from that office.⁹ Not surprising, considering the above commands from that office.

At 2243GMT the Itasca reported to Coast Guard San Francisco that the Tare 19 transmitter had been calibrated satisfactorily on 3195 kHz, that 355 kHz and 425 kHz were the best frequencies for Itasca’s vicinity, that 6210 kHz and 7500 kHz had been calibrated (on unspecified transmitters), and that testing would continue.¹⁰

At 0150 GMT, June 28th, Itasca reported to the CG office in San Francisco that the three ships were on their stations and communications for the flight were satisfactory. In addition, the direction finder was installed on Howland.¹¹ This is the only mention in the official correspondence to this point of a radio direction finder on Howland. Since George Putnam was in Oakland, and closely coordinating with the CG, it is possible that he relayed this information to Earhart via phone conversation.

On 2040GMT that same day, Itasca sent this message to Earhart: “ Itasca transmitters calibrated 7500, 6210, 3105, 500 and 425 kHz CW and last three either CW or MCW. Itasca direction finder range 550 to 270 kHz. Request we be advised as to time of departure and zone time to be used on radio schedules.”¹² This is the first indication of specific Itasca capabilities for transmission and direction finding provided to Earhart. Note that the Itasca was concerned about zone times, and wished to clarify any possible confusion, since the Itasca was working a half-time zone. This message was relayed to Earhart via Radio Tutuila, and received on the 29th.¹³

At 2015GMT, June 29th, Earhart sent this message to Itasca:

Plan midday takeoff here [June 30 local time]. Please have meteorologist send forecast Lae – Howland soon as possible. If reaches me in time will try leave today otherwise July 1st. Report in English, not code, especially while flying. Will broadcast hourly quarter past hour GCT. Further information later.¹⁴

Here, Earhart states that the time zone is to be GMT, that she wants reports from Itasca in voice and not Morse code, and she believes that there is a meteorologist aboard the Itasca. The meteorologist was actually in Pearl Harbor.

Fifteen minutes later, Earhart sent a telegram to George Putnam: “Radio misunderstanding and personnel unfitness probably will hold one day. Have asked Black for forecast for tomorrow. You check meteorologist on job as FN must have star sights.”¹⁵ Earhart is concerned about the weather forecasts (she hasn’t received any that are worthwhile), and is clearly concerned either about the radio protocol arrangements or about the time signals needed for Noonan’s calibration of his chronometers. Much discussion by various researchers as to the meaning of “personnel unfitness” has been put forth, without any consensus.

At 0300 GMT, June 30th, Radio Tutuila sent to the Itasca its schedule with radio Suva:

0115, 0400, 0930 GMT daily except Saturday and Sunday at Suva when only 0315GMT is scheduled. Have arranged for two additional schedules daily except Saturday and Sunday during Earhart flight at 2000 and 1030 GMT. Suva cannot schedule between 1200 and 2000 GMT as station is closed between these hours.¹⁶

Radio Suva is the main gateway for communication with Lae for Radio Tutuila.

Sometime just after 0400 GMT on June 30, Earhart sent this message to Black on the Itasca: “Account local conditions plan start July 1 2330 GMT if weather OK.” Earhart then tried to get Itasca to communicate directly with Lae so she can get a prompt weather report. “Now understand Itasca voice 3105 on hour, half hour with long continuous signal on approach. Confirm...”¹⁷ Here, Earhart is acknowledging the instructions from the CG San Francisco office.

Itasca responded at 0830GMT with this message: “ Itasca will transmit letter A with call letters repeated twice end every minute on half hour and hour on 7.5 MHz. Will broadcast voice on 3105 kHz on request or when within range.”¹⁸ Here, Itasca is repeating and confirming Earhart’s original instructions, but does not question the use of 7.5 MHz, which requires the use of code which Earhart does not want to hear.

At 2000GMT, Earhart sent this message to Black: “Ask Ontario to broadcast letter N for 5 minutes, 10 minutes after hour GMT at 400 kHz with own call letters repeated twice end every minute. Plan leave by ten this morning new Guinea time.”¹⁹This clarifies the radio schedule that the Ontario should follow.

Somewhat after 0200GMT, July 1, Earhart sent a message to Black stating that the take-off is delayed until 2130GMT July 1, she would appreciate a weather forecast, and to please notify Ontario of the schedule change.²⁰

This ends the various radio communication protocol procedures as discussed by the Itasca and Earhart. It is clear that the directions Earhart provided will be followed, regardless of whether they make sense, and that the time zones to be used are indeed GMT.