This computer-generated image depicts NASA’s Juno spacecraft firing its Leros-1b main engine – Image credit NASA

NASA’s Juno mission is inviting amateur radio operators around the world to transmit a coordinated message on the 28 MHz band to the Juno spacecraft.

NASA’s Juno spacecraft will fly past Earth on October 9, 2013 to receive a gravity assist from our planet, putting it on course for Jupiter.

To celebrate this event, the Juno mission is inviting amateur radio operators around the world to say “HI” to Juno in a coordinated Morse Code message. Juno’s radio and plasma wave experiment, called Waves, should be able to detect the message if enough people participate.

Juno will have a better chance of detecting the signal from many operators if the signal is spread out across the spectrum. The Juno Waves instrument is a broadband receiver, and the detector being used for this event has a band width of 1 MHz. It is better for detection of the signal to have a broadband signal coming in.

For this experiment, the Juno team would like to ask those participating to spread out in frequency across the 10 meter band. They have supplied a table of suggested frequencies between 28 and 29 MHz, based on the last letter of your call. When the HFR receiver is tuned to 28MHz, the center frequency is 28.5 MHz. A 50 kHz high pass filter limits low frequencies hitting the detector, so the frequency table excludes 28.5 MHz ±50 kHz. The natural signals the team expect to measure at Jupiter will consist of a large number of discrete tones, so spreading the signals out in this manner is a good approximation to the signals Juno is expected to detect. But at Jupiter, they don’t expect to be able to decode CW in the telemetry!

The 28 MHz band was chosen for this experiment for several reasons. The Waves instrument is sensitive to radio signals in all amateur bands below 40 MHz, but experience with the University of Iowa instruments on the Galileo and Cassini earth flybys shows significant shielding by the ionosphere at lower frequencies. As sad as it sounds, the team hope for lousy band conditions on October 9, so an appreciable fraction of the radiated energy escapes the ionosphere into space, and is not refracted back down to the ground somewhere else on the planet.

Juno’s antenna consists of a pair of tapered 2.8 meter long titanium tubes, deployed from the bottom deck of the spacecraft under the +X solar array and magnetometer boom. A high impedance radiation resistant preamp sits at the base of the antenna and buffers the signals from 50 Hz to 45 MHz. The elements are deployed with an opening angle of about 120 degrees. Ten meters is above the resonant frequency of the antenna and NEC analysis indicates a lobe generally along the spin axis of the spacecraft. This will be good for detection on the inbound part of closest approach to Earth.

The Waves instrument uses four receivers to cover the frequency range of 50 Hz to 41 MHz. Signals up to 3 MHz are bandpass filtered, sampled by A/D converters and FFT processed into spectra using a custom FFT processor developed by The University of Iowa under a grant from the Iowa Space Grant Consortium.

The Juno team point out that All transmissions must follow local and national regulations.

Please join in, and help spread the word to fellow amateur radio enthusiasts!

NASA – Say “HI” to Juno! http://www.jpl.nasa.gov/hijuno/
See How do I participate ? for the frequency list.