2024 Solar Eclipse TDOA Event

Ver 1.1  (4 Apr 2024 - Added Pre-Event Checklist)

Flash! Just revised to include Zoom link for coordination during the eclipse: Pre-Event Checklist V4 , authored by Steve, WA5FRF


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 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 or MP3 files on 40, 60, 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 (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.  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 

  • Just revised to include Zoom link for coordination during the eclipse:  Pre-Event Checklist V4, authored by Steve Cerwin, WA5FRF
  • Please review this PDF file, TDOA Operating Tips, authored by Steve Cerwin, WA5FRF.

Preparation - Before the Solar Eclipse

  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

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.

A test run was made on 30 Mar 2024.   Test Run details here.

A second test run could be held on 6 Apr 2024 at 1700UTC if there is interest.  Contact Steve WA5FRF if interested, steve@cerwinconsulting.com


Interest List

The following stations have recently 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
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 ?
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!