ARLA/CLUSTER: NASA convida radioamadores a transmitir mensagens para a nave Juno em 28 MHz

[João Costa > CT1FBF]

Radio hams to say 'HI' to Juno on 10m

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, we would like to ask those participating to
spread out in frequency across the 10 meter band. We 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 we 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 we expect to
detect. But at Jupiter, we don't expect to be able to decode CW in our
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,
we 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.

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.