Recording the Medium Wave Spectrum During Solar Eclipses
20 Jun 2023
Many in the medium wave (MW) listening community are eager to participate in HamSCI's efforts to better understand ionospheric dynamics, especially as they impact radio wave propagation. The upcoming North American solar eclipses of October 14, 2023 and April 8, 2024 will present excellent opportunities for listening stations to participate by recording IQ data from software defined radios. If you are interested in participating, please complete the pre-registration form at the bottom of this page.
This page details the background, purpose and how to participate in making and sharing those recordings. It is one of many events being held during the Festivals of Eclipse Ionospheric Science.
AM broadcast stations ideally transmit a continuous strength carrier at a fixed frequency. Therefore, changes in the carrier's frequency characteristics observed at a distant receiver are often due to changes in MW propagation between transmitter and receiver. Rapidly changing listening conditions during the upcoming solar eclipses will be indicative of a rapidly changing ionosphere, and broadband recordings made during the eclipse could be useful to researchers who want to gain a better understanding of the Earth's ionospheric dynamics.
AM Broadcast Band DXers know from past experience that the blocking out of radiation from the sun can introduce temporary night time listening conditions over an area far beyond the path of annularity or totality. During the eclipses, many MW hobbyists (who, in this capacity, will be contributing as citizen scientists) will be live listening as well as recording the entire medium wave band using software defined radios (SDRs), searching for unusual DX.
Multiple science questions might be investigated using IQ recordings made by AM broadcast band DXers:
- Is eclipse ionospheric response symmetric with regard to onset and recovery timing? Post-eclipse analysis may indicate that rate of signal strength increase (pre-eclipse) versus rate of signal decay (post-eclipse) differ. Confirmation of that phenomena may lead to theories explaining it.
- How similar is the eclipse effect on propagation (which occurs very rapidly, as the moon moves at supersonic speeds, crossing between the Sun and the Earth) to that of the daily dawn and dusk terminator passages (which occur slowly, as part of ordinary diurnal cycle)? Broadband recordings of the entire AM broadcast band - including sunrise, the eclipse event and sunset - could have great value.
- If SDRs are used that have their frequency determining components disciplined by an accurate and stable external oscillator, Doppler shifts caused by movement of ionospheric layers can be derived from apparent shifts in the frequency of the carriers of AM broadcasting stations. (A discussion of such Doppler shifts can be found at hamsci.org/grape.) Some of this recorded data may also be a useful input to another HamSCI experiment: “Tracking Traveling Ionospheric Disturbances Using Doppler-shifts of AM Broadcast Stations” (under development - please check back).
How to Participate
A number of SDRs commonly used by AM Broadcast Band DXers should be able to provide good scientific data from users’ IQ recordings, such as the Microtelecom Perseus, Elad S-2 and S-3, RFSpace SDR-IP, NetSDR and CloudSDR, SDRplay RSPdx, Winradio series of SDRs etc.
To obtain the best quality data using such receivers:
- Document receiver, software and antenna used, including as many details as possible of setup, such as front end attenuation settings.
- If possible, turn automatic gain control (AGC) off.
- Use your normal broadband antenna for receptions during the eclipse, but please do not change antennas or make any other changes to the system while recording. If you absolutely must make a change, that change should be fully documented.
- Time keeping will be very important. Make sure that timestamps in the recorded data are as accurate as possible by setting the computer clock to a known reference. Use of network time protocol software on the SDR's host computer would serve the purpose well (many recommend Meinberg NTP).
- Start recording well before maximum totality in your area, until well after that time. At minimum, please start recording one hour before the partial eclipse starts and finish one hour after the partial eclipse ends. The Solar Eclipse Circumstances Calculator for October, 2023 and for April, 2024 can tell you when the eclipse starts and finishes at your location.
- More helpful yet for researchers would be for DXers to record from six hours before to six hours after maximum eclipse annularity (2023) or totality (2024) at their location, as that time period will correspond to observations that will be made on the HF bands. For the truly committed, being able to record for 24 hours before the day of the eclipse and 24 hours afterward as well as the 24 hours on the day of the eclipse would provide “control days” to be compared with the time period around the eclipse.
- Warm up the receiver for several hours before starting recording, to minimize frequency drift in recorded signals.
- If your SDR can be locked to a frequency standard such as a Bodnar GPS Reference Clock, please use it, as that will improve data quality, and will make receiver drift less of a concern.
- If possible, make additional SDR recordings of, for example, two hours before and after sunset and sunrise on the day of the eclipse.
- As the actual eclipse is a unique event, doing trial run recordings in the month before an eclipse is encouraged, both at the time of day when the eclipses will occur, and during the more changeable receiving conditions near sunrise and sunset. Trial runs can help minimize errors on the eclipse days themselves.
Post-Eclipse Data Submission
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 detailed on this page.
Participants could suggest channels of further interest to researchers in the recordings, based on their own DX receptions, and from a preliminary look through the data, using software such as Carrier Sleuth or Data File Analyser. Perseus owners running Jaguar SDR will also have this capability. If participants have interest in learning more about processing their data, and how they might assist in analysis, guidance will be available from HamSCI members.
Please bookmark this page and join the HamSCI eclipse mailing list for future announcements related to the HamSCI MW Recording Event.