How to Collect Doppler Data With Your HF Radio
Radio signals provide a window into the changing ionosphere. The various signals from WWV, reflecting off the ionosphere, undergo changes in path length as the ionospheric electron density profile changes. This results in changes to the observed frequency of radio signals at receiving points, akin to the rise and fall in pitch of a passing train whistle.
Signals from radio station WWV reflect off the ionosphere in this illustration. Space weather affects how far a signal travels before it changes direction, and the receiving station detects this as a change in signal frequency.
Comparing the received radio signal with a precision local frequency standard, such as a GPS-disciplined oscillator, allows a user to measure these ionospherically induced frequency shifts. This measurement is prepared and recorded with open-source software. Numerous data sets recorded simultaneously from multiple locations offer information—when these data sets are examined both individually and collectively—about the ionosphere at the time the data are taken. This information includes the movements of traveling ionospheric disturbances and other important phenomena at various scales.
You can read more about how these measurements work here.
Collecting Doppler Data from Your Station
There are two ways to collect Doppler data from your QTH. One is to collect .CSV data using a frequency analysis program - this is best for long-term data collection. The other is to collect audio files, which is recommended only for short-term experiments such as eclipse festivals.
You will need:
- An HF radio and antenna capable of receiving signals from time standard stations
- A computer
- A sound card interface, like this one, to connect your computer to your radio. (How to check that your USB
External Stereo Sound Adapter is good for radio ? )
- A GPS-disciplined oscillator (GPSDO), like this one, to ensure the precision of your measurements
The method for connecting the GPSDO to your radio will depend on what kind of radio you have.
It is possible to collect data without a GPSDO, but your measurements will be much better with one. While you may be able to see trends in your data, you will not be able to make a quantitative estimation of layer height. As this chart by Steve Cerwin WA5FRF shows, a small error in your local oscillator frequency translates to a large error over time when estimating layer height:
You will want to record a beacon frequency that can be heard from your station. The examples on this page use 10 MHz. You can find a list of time standard stations here.
Radio time signal stations in the world with shortwave transmissions that you can use for Eclipse Festival of Frequency Measurement :
None with shortwave transmissions.
African countries in the northern hemisphere : use RWM in Russia
African countries in the southern hemisphere : try to receive one of the time signal stations in South America,
else use RWM in Russia
* BPM, China, Shaanxi, Pucheng (central China)
2.50 MHz, 5.0 MHz, 10 MHz, 15 MHz (Power in kW unknown for each frequency)
* HLA, South Korea, Daejeon
5.0 MHz (2 kW)
* RWM, Russia, Moscow, Taldom (east of Europe)
4.996 MHz (10kW), 9.996 MHz (10kW), 14.996 MHz (10kW)
* WWV, United States, Colorado, Near Fort Collins (central United States of America)
2.50 MHz (2.5 kW), 5.0 MHz (10 kW), 10.0 MHz (10 kW), 15.0 MHz (10 kW), 20 MHz (2,5kW), 25 MHz (2,5kW)
* CHU, Canada, Ontario, Ottawa (in the south east of Canada )
3.33 MHz (3 kW), 7.85 MHz (10 kW), 14.67 MHz (3kW)
None with shortwave transmissions.
Use WWVH in Hawaii or BPM in China
* WWVH, United States, Hawaii, Kekaha (in the center of the north pacific ocean)
2.50 MHz (5 kW), 5.0 MHz (10 kW), 10.0 MHz (10 kW), 15.0 MHz (10 kW)
* LOL, Argentina, Buenos Aires
10 MHz (2 kW)
* PPE, Brazil, Rio de Janeiro, Rio de Janeiro
10.0 MHz (1 kW)
* YVTO, Venezuela, Caracas
5.0 MHz (1 kW)
Recommendations for choosing the best radio station
1) use the nearest transmitter on your continent
2) use the frequency with the most power (in kW) if you can
3) for choosing the frequency to receive, try :
For continental and national radiocommunications we can summarize
- at night: bands from 3 MHz to 9 MHz,
- by day: bands from 5 MHz to 16 MHz.
For regional and departmental radiocommunications we can summarize
- at night: 0.3 MHz to 5 MHz band in Europe, 2 MHz to 6 MHz band in the tropics,
- by day: 0.3 MHz to 8 MHz band in Europe, 4 MHz to 12 MHz band in the tropics.
More detailed information by frequency band :
The propagation of electromagnetic waves depends of course on the medium but also on frequency. The ranges quoted below are given as an indication, the ionospheric propagation conditions being highly variable depending on the solar cycle, the time of year,the region of the world, the time of day, the circuits ...
Below 4 MHz: Communications are generally only possible at great distance when it is dark between the place of transmission and reception, after the disappearance of layer D. The ground wave has a predominant function, especially in below 1 MHz. Excellent regional strip at the start and end of the day with a range of up to 600 km (up to 2,000 km depending on conditions). Local connections can take place within a radius of a few tens of kilometers. Communications possible without jump distance in NVIS radiation.
4 to 8 MHz: intercontinental communications are possible (over 4000 km) but reliable links can generally only take place between 200 and 3000 km. Local connections possible up to about thirty kilometers. Communications possible without a zone of silence in NVIS radiation (Sky Wave with Quasi Vertical Incidence) with a range of less than 400 km for the lowest frequencies of this portion of the spectrum.
8 to 12 MHz: Open 24 hours a day for continental communications. Jumping distance from 300 km during the day to 1,000 km at night. Intercontinental communication possible when it is dark between the place of emission and reception.
12 to 16 MHz: Band open during the day with a range of up to 2000 km at all times. Communications possible to the antipodes during favorable periods of the solar cycle. Jumping distance varying from 200 km during the day to 1,600 km at night.
Approach #1: Collecting .CSV Data With fldigi
- Download fldigi, install it, verify that it's working correctly. Find the "frequency analysis" module in the "op mode" pulldown menu.
- Tune your radio (in AM mode) to a time standard station on 10 MHz, and determine which you can easily measure.
- Set your receiver's mode to USB (upper sideband) and tune to a frequency 1kHz below the carrier. For 10 MHz, tune to 9.999 MHz (9999.000 kHz - see image) and listen for the 1000 Hz tone.
- In fldigi, make sure that the tuned frequency in the upper left-hand corner is the same as your radio's frequency. To change it, click on the top half of a digit to increase it or the bottom half to decrease it.
- Look for the 1000 Hz line on fldigi's waterfall. Click the cursor there or use the offset frequency box at the bottom of fldigi's screen. You must set the number in the box at the bottom of the screen to exactly 1000. (If fldigi doesn't take this input properly, try starting the recording and then setting to 1000.)
- In fldigi, select the "Op Mode" menu and select "Freq Analysis" mode.
- Look for "writing CSV file" on the lower line of fldigi, toward the left. If you have a clean signal and see only one carrier, you should see a nice plot at the end of the day. If you see multiple carriers, more detailed Doppler information may be needed.
- Now, leave fldigi alone. While collecting data, leave your radio alone and make sure your computer is not shut down by an automatic update.
- At the end of your recording period, close fldigi. The file "analysis.csv" should be in your /fldigi/temp/ directory. Alternatively, they may be under "/fldigi.files/analysis". In MacOS, they are in the hidden directory ~/.fldigi/analysis - to find them, you must unhide the files using CMD + SHIFT + . in Finder. At the end of the data collection period, you should have one analysis-*.csv files for each day of data recording. Please rename these files by adding your name or callsign: e.g., analysis_200620 - W8EDU.csv. Do not edit the content of the files.
Note: This approach is for short-term data collection, such as during eclipse festivals. For long-term data collection, we recommend using fldigi as described above.