2024 Solar Eclipse TDOA Event

Ver 0.5  (11 Jan 2024 - Updated event dates for the new year)


The April 8, 2024 annular solar eclipse offers a unique opportunity to study an eclipse's influence on ionospheric dynamics, particularly on the layers of the ionosphere which are responsible for the propagation of radio waves in the HF (3-30 MHz) band. The science questions pertinent to this event:

  • What is the observed change in effective F2 ionization layer height caused by the momentary blockage of solar radiation?
  • Is symmetry observed in layer height changes when comparing 'before eclipse' and 'after eclipse' layer heights?   

Methodology:  Over propagation paths that support transmission of multiple hops, test waveforms can be used to measure HF signals' Time Difference of Arrival (TDOA) between multipath modes. For this event it is the 1- and 2- hop modes from the F2 layer that are of interest because:

  • F2 layer height is most sensitive to sunlight variations,
  • Simultaneous propagation of both modes frequently occurs on frequencies below 10 MHz, 
  • TDOA information can be used to infer F2 layer height. 

The test waveforms consist of very short pulses plus an audio chirp. They are reasonably simple to generate, transmit, receive and analyze by amateur radio operators.  A full explanation (theory, methods, on-air validation) of the TDOA technique is here on the HamSCI site.  The last page of that document contains references for further exploration.

HamSCI is actively recruiting dozens of stations capable of transmitting, receiving and recording WAV files on 40, 75 and 160 meters using SSB signals during the eclipse.  We are looking to have pairs of stations operating across North America.  Pairs will be located such that the stations may be on opposite sides of the eclipse path, parallel to the eclipse path or perhaps both at some distance from the eclipse path. (Small groups who wish to operate 'roundtable style' are also welcome.)  If you are interested in participating, please complete the pre-registration form below. If you have questions, send them to hamsci@hamsci.org.  Pre-registrants are listed below.  Please consider pre-registering so we can add your station to the list.

General Methodology

  • Look for WA5FRF and others on 7250, between 1130 and 1200 UTC on 8 Apr 2024.  If the frequency is busy, the group will slide up a few kHz.  If a major shift is needed, it will be announced on HamSCI's Google Group.  Other bands may come into play after the initial tests on 40 meters.  Again, watch HamSCI's Google Group for updates.
  • Participating stations will be asked to work in pairs or small groups.   
  • QSOs will established between at least two members of the group.  Others can simply listen, recording the chip audio, or they may choose to transmit their own chirp signals for others to receive/record, as in a 'roundtable' QSO.
  • A chirp waveform will be transmitted from one station to another multiple times during the solar eclipse period.  (Use enough power to consistently maintain a good signal.)
  • Options:  One station does the chirp transmitting (T), the other(s) the receiving/recording (R).  Even better would be to alternate:  Station A transmits, Station B receives.  Then, Station B transmits and Station A receives
  • Multiple T/R sessions are needed throughout the eclipse period.  A station should be prepared to transmit a chirp signal every 6 to 10 minutes, over 2 or more hours - for at least an hour prior to maximum annularity near your QTH, and for at least an hour after.
  • Save received files with callsign, date and time stamps in their names (eg W5XXX-14 Oct-1650Z.WAV)
  • Help the HamSCI science team with the results analysis - we'll gladly teach you how!

Operating Tips - for Successful Transmitting and Receiving 

Preparation - Before the Solar Eclipse

  • Please pre-register as a TDOA Event participant.  There is no obligation for pre-registration, but doing so helps the study authors gage interest and the geographic dispersion of interested parties.  You are welcome to identify the stations with whom you would like to operate during the TDOA Event.
  • Verify that your station can cleanly transmit and/or receive WAV files.  A sound card interface (eg SignaLink, microHAM), or a radio which appears as an audio device over USB (eg Icom 7300, 7610, Elecraft K4 series, Kenwood TS-590SG) will work equally well.
  • For transmitting stations, visit this GitHub site, run the Jupyter notebook code in binder and follow the instructions for generating a 'chirp file' (sample file below) having your callsign and Maidenhead grid square embedded in Morse code.  binder runs in the cloud - the only files you will need to download are two ouput files (one each WAV and CSV).  (Here is a sample binder screen running the Jupyter notebook for chirp file generation.)
  • For receiving stations, prepare a directory on your shack computer for storing the WAV files (which we will ask you to upload to the HamSCI/TDOA data data repository after the eclipse).
  • Plan your solar eclipse operating around the time when the eclipse path is closest to your QTH. GreatAmericanEclipse.com provides detailed path information. 
  • Join the WWV-H Science HamSCI Google Group so you can receive announcements from the principal investigators of this experiment
  • Sample test signal (WAV file, ~40 seconds long) consists of a brief period of white noise, 'DE', callsign and Maidenhead grid locator (each sent three times) in Morse code, followed by the chirps.  We suggest right clicking this link, and choosing 'Open in a new browser tab (or window)':  SEQP Test Signal for AF8A in EN91GN

Test Runs

Eclipses are infrequent events.  Opportunities to study them are few and far between, so we need to be fully prepared for eclipse day.  HamSCI strongly encourages all TDOA participants, especially transmitting stations, to perform a 'dry run' well before the actual eclipse.  This will give everyone a chance to check out their hardware and software, make adjustments and updates, well in advance.

Test runs occurred on 30 Sep 2023 and 7 Oct 2023.  For the record, the details are  here.

Interest List

The following stations have expressed an interest in participating.  As participation is 100% voluntary, this list may change right up to the day of the event(s).

Callsign Location Grid Band(s)
WA5FRF Mico, TX EL09nn 40, 75
TI4JWC Santa Barbara, Heredia EK70wb 40
KD8ABX Ann Arbor, MI EN82dh 40
W3OA Mooresville, NC EM95nm 40
KD8RV Grosse Pointe Park, MI EN82mj 40
WV5L Woodstock, GA EM74sc 40
W5AC College Station, TX EM10tp 75
KD2LOF New York, NY FN30ar 40
K1FR Alexandria, VA FM18kt 40
PT9CA Campo Grande, Ms GG29ro 160
WP4BQV Ripon, North Yorkshire, UK IO94fd 40
Who will join next? ? ? ?


Reporting Results

The research community uses various public databases to store data collected in these events.  They allow for open access, and long-term (many years') storage.  Once the database has been chosen and upload procedures established, they will be shared with all participants and detailed here.

Scoring and Post-Event Recognition

Unlike other the other events to be held during the Festivals of Eclipse Ionospheric Science (add link), the TDOA Event is not a competition.  All participants will be acknowledged via listings on the HamSCI website.  There is the possibility that one or more participating stations will receive mention in future studies, presentations and research papers.  Regardless, everyone will earn the gratitude of the ionospheric science community.  Only through experimentation, data gathering, rigorous analysis and sharing of results can we make progress towards understanding the physical world in which we live and operate our stations.


  • The TDOA Event stems from work originated by Steve Cerwin WA5FRF with assistance from the WWV/H Scientific Modulation Working Group.
  • Code for generating the chirp file is courtesy of Aidan Montare KB3UMD and Dr. Kristina Collins KD8OXT
  • Web page authored by Gary Mikitin AF8A

Pre-Registration Form

This is a Google form.  It will record your e-mail address and ask you if you want to receive a copy of your responses (recommended).  Thank you, in advance, for your interest in participating in the HamSCI TDOA Event!