WKU Radio Jove Remote Station

In the basic Radio Jove setup, incoming radio waves close to the 20 MHz resonant frequency (15 meter wavelength) of two horizontal dipole antennas induce small (microvolt) electrical signals in the antenna wires that are transmitted down coaxial feed lines to a radio receiver, where they are amplified, mixed down to audio frequencies, filtered and amplified further, and finally output to standard audio jacks for live listening or recording. The direction in which the dipole array is most sensitive can be adjusted in azimuth by the orientation of the individual dipole antennas and in elevation by adjusting the antenna heights and the relative lengths of their feed lines. The area of maximum sensitivity (the "beam") is huge by radio astronomy standards (about 120° × 60° = 2.2 steradians in the configuration used here), but the low gain of such a broad beam is offset by the ability to monitor emissions from Jupiter or other targets for several hours without having to track their motion across the sky, which would carry them through a narrower beam more quickly.

WKU's Radio Jove experiment was adapted for remote operation to minimize contamination of the received signal by radio frequency interference (RFI) from power lines, computers, and other artificial sources commonly found where people live or work. The WKU RJ remote station was thus completely battery-operated and as isolated from RFI sources as was practical. It was located on private land near WKU's Bell Observatory, approximately 10 km SW of the city limits of Bowling Green, KY. The antenna array and receiving equipment were located 150 meters ESE of the optical telescope dome, which has its own power lines coming in from the west and a small microwave tower for internet connectivity. The nearest residential property was 800 meters to the west, over a hill. The nearest cell tower was 2 km SSE.

2011-2012 Observatory Site with Optical Dome in Upper Left and RJ Tent in Lower Right (Google Maps)

2014-2015 Tent Exterior with Dual-Dipole Array

Inside Tent with 12V Battery, Noise Source, Receiver, and Recorder

• Antenna + Feed Line: Assembled from RJ 1.2 Antenna Kit (RJA). Includes two horizontal, parallel, center-fed dipole antennas made of #14 gauge 7-strand copper wire, suspended 10 feet above ground by four aluminum masts, and connected by RG59U coaxial cable feed lines, with 3/8 wave delay on one for phasing, through a power combiner/splitter. Line losses are estimated at 1.5 dB (factor of sqrt(2) in signal amplitude). Beam directivity is described above; particular configurations are described below.

• Noise Source + Bandpass Filter: An RF-2080 C/F calibrated noise source and bandpass filter was placed between the feed line and the receiver. When switched on, this replaced the antenna signal with a known amount of noise power, which could compared to the antenna input to determine how much power was being received in normal observations. Both the noise and antenna signals were sent through a bandpass filter to eliminate RFI from strong broadcast stations. This filter added another 1.5 dB of attenuation to the signal path.

• Receiver: The RJ 1.1 receiver (RJB kit, pre-assembled) has a tunable bandwidth of 300 kHz centered at 20.1 MHz and an instantaneous bandwidth of 7 kHz at radio frequencies (half of this at audio frequencies, since it is a direct-conversion design). A gain (volume) setting of 0.5 was normally used, which sufficed for capturing both faint Jupiter storms and loud Solar bursts; terrestrial broadcast signals can be even stronger but are still within the dynamic range of the recording equipment. The RJ receiver draws 0.72 W of power.

• Audio Output: The receiver has two audio jacks, allowing simultaneous live monitoring and recording. Auvio 3300090 Headphones were used for live monitoring and for later playback of recordings. For the latter, a TASCAM DR-40 portable digital recorder samples audio output from the receiver at 44.1 kHz with 16-bit depth in a single (mono) channel, writing this to consecutive uncompressed WAV files, in which format it can store up to 100 hours of continuous observations on its 32-GB SDHC memory card. Data extraction and processing are described below. The DR-40 draws about 0.78 W of power as used here, so the total power drain of the receiver + recorder was about 1.5 W.

• Power: Starting in 2013, a QuickCable Rescue 1800 Jump Pack rechargeable 12-volt, 40 amp-hour battery powered all electronic gear, including the receiver, noise source, and digital recorder, via an assembly of Enercell cigar-lighter plug adapters with 2A, 250V slo-blow fuses. Both the receiver and noise source are designed for 12V power. In 2011 and 2012, the recorder was run off 3 internal AA cells or 6 AA cells in an external pack (model BP-6AA), but the latter was adapted to accept 12V input to its DC switching power converter in 2013; field tests show no measurable RFI increase from this arrangement (the 12V power for the receiver was also run through an alternator whine filter to minimize noise feeding back from the BP-6AA converter). The 12V battery can power both the receiver and recorder for 10 days of continuous operation in cold weather with 75% charge capacity (the noise source was run only for brief field calibrations). This was a great improvement over AA battery life for the DR-40, which ranged from about 8 hours for 3 alkaline cells to about 30 hours for 6 lithium cells.

• Housing: All electronic gear was housed in a tent to shield it from the elements and kept in plastic storage tubs that both cover from above in case of a tent breach and protect from below in case of flooding. The most durable tent was a Springbar 7'×8' Outfitter 3 canvas model. Inexpensive nylon dome tents were used for shelter initially, but these (a) had screened areas that could not be fully sealed, letting in rainwater that pooled on the tent floor, and (b) were not robust against long-term exposure to wind and sunlight, necessitating regular replacement and risking equipment damage. Aside from the tent and storage tubs, no environmental controls were provided for temperature or moisture, but the equipment performed well in dry and wet weather, from 20° to 90° Fahrenheit.

The WAV files written by the DR-40 encode the raw signal wave-form as a digital representation of the voltage as a function of time. These were read with a C code using the libsndfile package, squared, and averaged over a set of equal time intervals (typically a second or more) to obtain an uncalibrated estimate of the received power, which by Ohm's Law is proportional to the square of the signal voltage. The power could then be calibrated by comparing sky observations to others of the calibrated noise source and assuming simple proportionality (tests of different receiving gear configurations indicate that this is reasonable). The standard calibration is in temperature units, but these can be converted into flux units or received power if the antenna beam is well understood. The data timestamps were also calibrated against recorded WWV time announcements. Plots of received power vs. time could then be generated from the calibrated data using custom routines in C, CSH, and Supermongo. As an option, some brief RFI spikes from radiosonde band sweeps could be excised from these plots (but not the WAV recordings) by median filtering of the waveform data with 3-sigma clipping before squaring the voltages to get power.

Both plots and audio recordings were subsequently reviewed for Jupiter and Solar activity. The Radio Jove email list is a valuable resource for checking the local results against those of other RJ observers.

The WKU Radio Jove remote station was run on an intermittent basis since first established in the fall of 2011 as part of the Honors General Astronomy 214 course. Several attempts were required for the station to attain full operations.

• The original 2011 setup used two east-west dipoles at 10-ft. elevation, with a 3/8-wave (135° phase) delay in the southern dipole feed directing the beam to a point 50° above the southern horizon to observe Jupiter crossing the local meridian (a weaker secondary beam pointed 35° above the north horizon, but Jupiter does not pass through this part of the sky as viewed from the northern hemisphere).

  2011 RJ Tent and Dual-Dipole Array

  Antenna Array Layout (RJ Antenna Manual)

  North-South Sensitivity Pattern (RJ Antenna Manual)

  Half-Power Beam on Sky (Radio Jupiter Pro)

  The experiment was limited by not having long-term power for the DR-40 recorder (6-9 hours for internal alkali AA batteries, or twice this for the external BP-6AA pack), nor any power for the noise source in the field. In addition, data could only be listened to as audio playbacks or by viewing signal amplitudes inside audio-manipulation software like Audacity (the standard software for handling RJ data is Radio SkyPipe, but it requires a Microsoft Windows platform that could not be supported locally). Even so, several short observations were made over a period of weeks, and Jupiter S- and L-burst activity was captured. The electronic gear was removed during the winter, and the antenna array was taken down and stored in late spring.

  2012 RJ Tent and Dipole Array The experiment was repeated in the fall of 2012 with a new ASTR 214 class. The same antennas were put up again in the same configuration, and the same equipment was used, but a new tent was needed to house the gear, since the previous tent had not survived the spring 2012 storm season. Although the fall 2012 observations were heavily time-constrained, some Jupiter activity was again captured. Observations were also taken in a more continuous mode by visiting the site frequently to replace batteries, and by using lithium cells in the BP-6AA, which enabled the DR-40 to run for up to 30 hours. In parallel, code was developed to read the WAV files and compute (still uncalibrated) received power vs. time for analysis. At the end of the season, gear was stowed as before, but the tent and antennas were left in place.

  2013 RJ Tent and Dipole Array In the fall of 2013, the experiment was repeated again for ASTR 214, but with the ability to power the receiver, calibration noise source, and recorder together off the 12V battery. This allowed for the first true long-term observations, spanning 8 continuous days. Bad luck intervened however. First, signal quality was hobbled by feed line damage from a lawn mower at the start of the season. Then the antenna array was damaged in a severe storm. Later, the tent (a replacement for the 2012 tent, which had also not survived the off-season) was torn loose from its moorings and deposited intact in the woods east of the site. It was moved back and anchored more securely but was torn beyond repair in subsequent storms.

  In 2014, the experiment was revived for a fourth ASTR 214 class, but on a much more solid footing. First, in place of the prior nylon dome tents used to house equipment, a new high-quality canvas tent was purchased to allow for longer-term stability of operations. 2014 RJ Tent and Array East-Facing Beam Area Second, a new antenna array (dipole wires, insulators, masts, feed lines, etc.) was assembled from scratch. The array was configured as in 2011-2013, but with the two dipoles oriented north-south and a 3/8-wave delay in the eastern dipole to capture Jupiter in the early morning sky, since it would not cross the local meridian before sunrise until very late in the year. This setup proved very successful, recording almost continuously for many weeks and capturing numerous Jupiter storms, Solar flares, and sudden ionospheric disturbances. As a result, students were able to carry out in-depth data analyses in addition to the hands-on experience of setting up the station that they had in prior years.

• In 2015, more observations were made with the same experimental setup in the spring and summer and also for a few days in the fall with a new ASTR 214 class. The equipment continued to perform well, adding to the growing body of recorded data, which had multiplied greatly in the past year. To address this data glut, new methods were developed to plot large masses of continuous data. The combination of broad time coverage and the means to visualize it at last enabled the positive detection of Galactic emission and, quite unexpectedly, the tracking of long-term changes in Solar activity.

• In the spring of 2016, the station was dismantled and its components placed in storage to allow the land to be used for other purposes. Jupiter's location in its orbit placed it on the far side of the Sun during the fall semester when ASTR 214 was taught, visible only briefly before or after sunset, so that fresh observations for the course would be difficult. Instead, efforts were focused on processing, visualizing, and reviewing the backlog of the many hundreds of hours of RJ observations accumulated in the previous 5 years. Plots of these data are available for viewing.

Future observations are planned as circumstances allow.

Please see the credits page for a list of the many individuals who have helped with this project. The photo gallery gives many more photos of the station and the people involved. The history page describes earlier radio astronomy experiments at WKU.