2024 Solar Eclipse TDOA Event

Ver 1.2  (10 May 2024 - Removed 'day of event' info.  Added doc on results analysis)

Updates:  Download the new document on TDOA Chirp Analysis  and see comments on Reporting Results


The April 8, 2024 annular solar eclipse offered 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?   

General Methodology 

Over propagation paths that support transmission of multiple hops, test waveforms were used to measure HF signals' Time Difference of Arrival (TDOA) between multipath modes. For this event it was the 1- and 2- hop modes from the F2 layer that were 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 consisted of very short pulses plus an audio chirp. They were reasonably simple to 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 recruited dozens of stations capable of transmitting, receiving and recording WAV or MP3 files on 40, 60, 75 and 160 meters using SSB signals during the eclipse, looking for pairs of stations operating across North America.  Pairs were located such that the stations were on opposite sides of the eclipse path, parallel to the eclipse path and at some distance from the eclipse path.   A sample of the pre-registrants is listed below.  

Operational Details (Manual method, transmit and receive)

  • Dawn transition measurements:  Look for WA5FRF and others on 7250, at 1200 UTC on 8 Apr 2024.  
  • Eclipse measurements:  Look for WA5FRF and others on 7250, at 1600 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.  Connect to the day-of-event Zoom meeting 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.  Here is a paper on a manual method for analyzing TDOA results: 2024-05-04 TDOA Chirp Analysis for NVIS.docx

Operating Tips - for Successful Transmitting and Receiving 

Preparation - Before the Solar Eclipse (8 April 2024)

  1. 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.
  2. Verify that your station can cleanly transmit and/or receive WAV or MP3 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.
  3. For transmitting stations, create and test to be sure your computer (or HF transmitter) can load and play the Science Payload files noted in #4, below
  4. If you will be participating in the HamSCI TDOA as a transmitting station during the upcoming eclipse, please generate this new personalized .wav file for your use.  This file has many modifications made from the previous file we used during the 2023 annular eclipse.  The changes were made to permit a more robust data recovery.  The link to create the new .wav file can be found by clicking on the README file at the bottom of:  https://github.com/jtm5/HamSCI_TDOA_SigGen
  5. For receiving stations, prepare a directory on your shack computer for storing the recordings (which we will ask you to upload to the HamSCI/TDOA data repository after the eclipse).
  6. Plan your solar eclipse operating around the time when the eclipse path is closest to your QTH.  NASA's Eclipse Explorer can provide detailed path information. 

Here you can listen to a test waveform (~18 seconds long) consisting of a 1 KHz 'calibration' tone, white noise, short pulses, ten repetitions of the 'chirp' signals, more white noise and another 1KHz calibration tone.  We suggest right clicking the appropriate link, and choosing 'Open in a new browser tab (or window) to listen or download.

Mac OS:   SEQP Test Signal_v5_Science-payload.wav

Windows OS:  SEQP Test Signal_v5_Science-payload.mp3


Interest List

The following is a sampling of stations who expressed an interest in participating. 

Callsign Location Grid Band(s)
WA5FRF Mico, TX EL09nn 40, 75
TI4JWC Santa Barbara, Heredia EK70wb 40
KD8RV Grosse Pointe Park, MI EN82mj 40
K1FR Alexandria, VA FM18kt 40
DL4AD Fuerth, Bavaria, Germany JN59ii 40
KG5AHJ Austin, TX EM10ag 40
KK7MVD Burlen, WA CN87uk 40
K4GWA Rochester, NY FN13ed 40
N3BEV Indiana EN60wl 40
K9OTA Carbondale, IL EM75jr 40
W7CAM Wisconsin EN52fu 40
KC1IWA Vermont FN34tp 75
N5DUP Texas EM02ch 40
N1OG NH FN42ft 40
W8EDU Cleveland, OH EN91em ?
W3USR Scranton, PA FN21ej ?


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 via email.  If you have questions about where or how to upload data, please contact Steve Cerwin or hamsci@hamsci.org

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