Spacecraft Probe to Listen for ARRL Field Day Signals
Stephen Bellner
The Enhanced Polar Outflow Probe (e-POP) onboard the Canadian Cascade Smallsat and Ionospheric Polar Explorer (CASSIOPE) satellite will again support Amateur Radio citizen science by participating in ARRL Field Day 2017, June 24-25. The HamSCI citizen science initiative says that, from a radio science perspective, Field Day is an ideal time for e-POP to study the structure of Earth's ionosphere using participants' transmissions. HamSCI was started by ham scientists who study upper atmospheric and space physics.
One
of e-POP's
instruments is the Radio Receiver Instrument (RRI), a digital
receiver with
four 3-meter monopole antennas. Its scientific objective is to
study
natural and artificial radio emissions from 10 Hz to 18 MHz. The
receiver's
monopoles can be electronically configured into a crossed-dipole
setup, and it
has two data channels -- one for each dipole. Each channel is
sampled at
62.5 kHz and passed through a 30-kHz bandpass.
During Field Day 2015, the receiver was activated for 2 minutes while e-POP was just north of Milwaukee, on a southeasterly heading. It was in a crossed-dipole configuration, with its two channels tuned to 3.525 and 7.525 MHz, respectively. A spectrogram that summarizes the results shows that not only were CW transmissions visible on the 40-meter channel (B), but they were only observed for about the first 30 seconds, even though the Reverse Beacon Network (RBN) showed that these stations transmitted throughout the experiment period. No signals were received on the 80-meter channel (A), and, at least theoretically, those signals should not have been able to penetrate the ionosphere and propagate to the receiver during the experiment.
The
signals heard can be used to study HF propagation, and the
advantage of using Amateur Radio transmissions is that call signs
readily
identify a signal's source, which can be fed into a HF ray trace
model, and
then used to elucidate the properties of the ionosphere during the
experiment. During Field Day 2015, 23 call signs were identified.
One hypothesis under investigation is that the ham signals disappeared as the spacecraft headed south into latitudes where the ionosphere was denser and blocked the transmissions.
For Field Day 2017, e-POP will dedicate all of its resources to studying HF radio wave propagation using ham radio transmissions. The Radio Receiver Instrument rwill be tuned to the 40- and 80-meter CW bands, although precise frequencies have not yet been determined. It is scheduled to be activated six times, in 10-minute increments, over Field Day weekend. Read more.