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FO-29 Digi-Talker Question and Answer

by Mike Gilchrist,KF4FDJ 

The Japanese satellite, Fuji Oscar 29 (JAS-2), was launched on August 17, 1996, by H-II rocket No.4, along with the earth observation platform satellite ADEOS, from Tanegashima Space Center of NASDA (National Space Development Agency of Japan).

FO-29 is a small LEO (Low Earth Orbit), Japanese owned satellite containing a digitalker, mode JA transponder, and 1200/9600 baud packet capabilities. The mode JA transponder requires a SSB, or CW uplink signal on 2 meters, and transmits a downlink SSB/CW signal on 70 centimeters. Mode JA is a full duplex mode. You WILL hear your own downlink, which is crucial, in order to compensate for Doppler. The satellite is also capable of mode JD, (digital) at 1200/9600 baud. 

Q.Is Fuji Oscar 29 always in digitalker mode, and what is it?

A.  The digitalker on FO-29 is a digital loop announcement, which makes the same announcement over and over. You will hear, "Ho- ho'kke'kyo, this is JAS two." The first part is the song of a bush warbler. JARL (Japanese Amateur Radio League), plans to cycle digitalker, mode JA, and mode JD. The digitalker message is subject to change. Check announcements on AMSAT-BB for a mode schedule and other details.

Q.Do I need a multimode rig to hear the digitalker?

A.Since FO-29 transmits in FM mode while in digitalker, any FM or multimode receiver capable of tuning the 70 cm ham band should be able to detect the signal.

Q.Do I have to use a high gain antenna to hear the signal?

A.Digitalker operation dedicates most of the power budget of the satellite to the FM transmitter, instead of spreading it across a mode JA transponder. It is a very strong signal! It is possible to hear the satellite with a handheld scanner or transceiver, and a stock "rubber ducky" antenna. Most 70 cm base stations, or scanner listening posts, with fixed antennas, should also be able to tune the signal.

Q.I've heard that a circularly polarized antenna is necessary to hear FO-29. Is this true?

A.While a circularly polarized antenna will help on mode JA, it is not necessary with the digitalker. It REALLY is possible to copy the signal with a handheld device and a "rubber duck" antenna. We have been successful with a Yaesu FT-50R and a stock antenna. You will need to rotate the rig (and antenna) for the best orientation. Experience shows that horizontal polarization, with the axis of the antenna perpendicular to the satellite gives the best reception. Experiment!

Q.Where do I tune to hear the signal?

A.The transmit frequency is 435.910. Of course, you will have to compensate for Doppler shift. Just remember you will tune a little higher in frequency as the satellite approaches your position, and a little lower in frequency as it recedes. You will always be tuning higher in frequency when the satellite comes over the horizon. Make sure you have your radio set to tune small increments, as increases and decreases in Doppler are gradual, and linear.

Q.How long will I be able to hear the satellite during each pass?

A.Since FO-29 is a low earth orbit satellite, most passes will be between 6 and 18 minutes in duration. Timing is critical in working any amateur satellite.

Q.What is the purpose of the digitalker?

A.The digitalker presents an easy opportunity for hams and non hams to have their first taste of real time reception of signals from space. Use this opportunity to show a child, or a terrestrial ham how easy it can be to tune a satellite. This opportunity is excellent for scout meetings, monthly ham meetings, schools, or any place where inquisitive persons congregate.

Q.How will I know when the satellite is over my location?

A.You will need a program to generate predictions of when the satellite is "visible" to you. An excellent place to find downloadable software for real time tracking of satellites, and other information on the amateur satellite program in general, is:http://www.amsat.org/. Be sure to download the latest keplerian elements if you download a tracking program. Each prediction program needs these coordinates to determine where the satellites are and to help you determine when FO-29 will be over your horizon.

If you have any comments, additions, or modifications to this document, please contact me directly. We will attempt to post the latest version whenever the satellite is toggled to digitalker mode.



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Last update March 10, 2001 -N7HPR

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