The basic challenge for this experiment is to get radio waves transmitted from our radar to be received by Fort McPherson. However, variations in the height and density of layers in the ionosphere as well as how these factors change with the wavelength of the radio wave propagating through the ionosphere make it difficult to predict what location the transmitted pulses will come back to the ground. Some effort to predict where our signal will reach the ground has been made using the ray-tracing tool located on our website at: link)

In order to perform this experiment, our radars needed to use one single frequency as the transponder at Fort McPherson can only be set to one frequency every 30 seconds. Normally a SuperDARN radar has a small frequency hopping routine that searches for the quietest frequency and then transmits on this frequency. In order to override this frequency hopping, a couple of lines of code were added to the normalscan control program which were already present in the themisscan control program. These lines included initializing a new variable called 'fixfrq', adding a OptionProcess line to read in the variable value from the scheduler command line and lastly setting fixfrq to the transmit frequency just after the clear frequency search. For the last part, an if statement works well to gate valid values for fixfrq as well as enabling and disabling the override. For example, if fixfrq is set to zero, that's not a valid transmit frequency AND its an indication that the transmit frequency found in the clear frequency search should be used.

As seen in the scan plot above and the range-time plot below, it's believed that with both Fort Hays West and the transponder set to 14.800 MHz, a link between the two sites was established for a period of time. During the time shown here, the transponder was repeating received signals at a +50 and -50 Hz shift simultaneously. It is unsure of how a SuperDARN radar would interpret a signal with both a positive and negative shift, but this amount of frequency shift would show up with a magnitude of about 500 m/s. The scatter from the Fort McPherson area on the morning of Feb. 14 has velocities that approach the calculated value.

This is the only time period that it is believe the Fort Hays radar was able to get a signal to the transponder at Fort McPherson during this experiment. Some suggestions have been made to Paul Bernhardt on how to better setup the transponder for a SuperDARN radar. Another similar experiment is hoped to be conducted sometime in May.

Timeline of Events

  • Feb. 13, 2012, 16:40:11 utc: FHW begins operating at a fixed frequency of 14800 kHz

  • Feb. 14, 2012, 00:00:10 utc: FHW begins operating with a themis camping beam on beam 12. Frequency is still fixed at 14800 kHz.

  • Feb. 14, 2012, ~03:30:00 utc: Transponder is set to 14800 kHz with a +50 and -50 Hz shift and a delay of 20.149 nmi (37.316 km) to the transmitted signal.

  • Feb. 14, 2012, ~14:36:00 utc: Possible transponder returns on FHW seen in beams 11 and 12. Maximum Doppler shift measured corresponds to a 50 Hz shift.

  • Feb. 14, 2012, ~21:07:00 utc: Planned to set the transponder to just one frequency shift after concern about +/- shifts at the same range.

  • Feb. 14, 2012, ~22:37:00 utc: Transponder frequency changed to 10500 kHz. Planned to change the frequency back up to 14800 kHz.

  • Feb. 15, 2012, ~21:30:00 utc: Frequency of transponder to be set to 10800 kHz once the local contact in charge of manning the transponder was done for the night.

  • Feb. 16, 2012, 02:00:12 utc: FHW begins operating with a fix frequency of 10800 kHz, themis camping beams still set on beam 12.

  • Feb. 17, 2012: 12:00:12 utc: FHW returns to normal operating frequencies and camping beams.