AmateuRadioMalaysia

Sunday, December 25, 2005

Do you know Series - 11









It is a common perception that it requires sophisticated equipment and large circularly polarised antenna arrays to work amateur satellites. There are several low Earth orbiting satellites which can be worked with relatively simple transceivers and antennas.

More recently, some satellites have been carrying crossband FM repeaters instead of linear transponders. These repeaters are similar to their familiar terrestrial cousins in that they receive an FM signal on a specific channel, demodulate the signal and retransmit the signal on a new frequency. These satellites can only carry one QSO at a time.

To successfully work an amateur satellite, you need to have transceivers suitable for the satellites you wish to work. For the FM repeaters, either a dual band FM transceiver with crossband transmit/receive capabilities or separate 2m and 70cm FM transceivers are suitable. All of the FM satellites (operational or proposed) use 2m and 70cm, with one of these bands being used for the uplink, the other for the downlink.

There are a wider variety of frequencies in use by linear transponder satellites. The suggested bands to try for a first attempt are 2 metres uplink and 10 metres downlink. Example:

AMSAT-OSCAR 51 (Echo or AO-51)
Analog Uplink:
145.920 MHz FM (PL - 67Hz)145.880 MHz FM QRP (no PL)1268.700 MHz FM (PL - 67Hz)
Analog Downlink:
435.300 MHz FM2401.200 MHz FM
PSK-31 Uplink
28.140 MHz USB
Digital Uplink:
145.860 MHz 9600 bps, AX.251268.700 MHz 9600 bps AX.25
Digital Downlink:
435.150 MHz 9600 bps, AX.252401.200 MHz 38,400 bps, AX.25
Broadcast Callsign:
PECHO-11
BBS Callsign:
PECHO-12
Launched
June 29, 2004
Status: Operational

For antennas, an existing HF dipole and VHF/UHF omnidirectional antennas will work in a pinch. The typical VHF/UHF collinears typically have a low angle of radiation, and better results may be obtained with a simple ¼ wave groundplane, or for the more serious, a turnstile antenna. If you have crossed Yagis and AZ/EL rotators, all the better (but then this article isn’t aimed at you in this case! :-) ). Finally, though not essential, it is very strongly recommended to have a computer, satellite tracking software and an Internet connection available. The Internet connection is for downloading the latest Keplerian elements for the tracking software (and the software itself if you don’t have any), as well as checking satellite home pages for transponder schedules and other information. Besides, the Internet is fun when the birds aren’t overhead!

Working your first satellite! This isn’t anywhere near as daunting as it sounds. The first thing is to have a look around your shack and see what equipment you have. If, like many amateurs, you have FM only radios on VHF/UHF, then you are limited to the FM satellites. The rest of this article will concentrate on FM operation as nearly everyone has FM gear for 2m and 70cm, and the operating techniques are easier to master.

First, time for an inventory, as the gear you have available will partially determine the satellite to use. Regardless of the rig you use, it has to be capable of tuning in 5 kHz or smaller steps, to enable you to follow the Doppler shift as the satellite passes overhead.

Home operators will most likely use their existing omnidirectional or beam antennas. Modern omnis tend to have a very low angle of radiation and therefore may not give good results when used to work satellites. However, as most modern rigs put out 35-50 watts on 70cm, the extra power should largely compensate for the antenna’s radiation pattern. If you can use a ¼ wave or turnstile though, then you’ll enjoy better satellite performance. If you have a beam, you will need to track the satellite as it passes, especially at low angles, where the beam’s gain will be useful. And finally, don’t forget an earpiece or headphones. You will be operating full duplex (i.e. being able to transmit and receive simultaneously) and without headphones, feedback can be a problem. With them, you’ll be able to hear what you sound like while you transmit, which will be helpful for correcting for Doppler shift.

Only one person can use the transponder at a time and the satellite is usually only accessible for about 10 minutes. Others will appreciate your efficiency and courtesy. Most FM satellite contacts are usually an exchange of callsigns, signal reports and occasionally a comment about the weather.

The typical station is:
Uplink - Icom IC-T81A handheld running 3.5 watts into a 70cm 1/2 wave ground independent handheld whip.
Downlink - Alinco DJ-500T handheld or Standard C58 all mode portable with a "ScanDucky" scanning antenna (roughly equivalent to a 1/4 wave on 2m).

However, a word of warning: For some people, the thrill of satellite operation can be addictive! You may find yourself trying unusual situations, or decide to invest in multimode gear and work some of the linear 'birds' that are up there. You have been warned! (and I have the audio clips and 2m all mode box to prove this theory!) :-)

Courtesy & edited from AMSAT Web page :
http://www.amsat.org/amsat-new/information/faqs/langdon.php




1 Comments:

  • Hello All,

    First of all a very Happy New Year to all of you.

    On the 9th of January 2006, at 0136 Hours Malaysian Standard Time or 1736 Hours UTC, I managed a QSO with William McArthur (KC5ACR) on board the International Space Station (ISS).

    Please visit http://www.9w2qc.net/issqso/ for more details.

    I am also happy that this QSO has served three points:

    1. That the 1st station he worked from Malaysia is a 9 WHISKEY station. This shows that 9W are also capable of out of earth communications.

    2. That the astronauts do not turn off the radio over Asia as claimed by some parties.

    2. That the QRM over Asia is not as bad as claimed by some parties. Bill himself said that it is not as bad as over North Africa and Europe.

    Thank You.

    73,
    Sion Chow Q. C.,
    9W2QC.

    Strong supporter of the abolishment of the Morse Code requirement to obtain a full license!!!

    Support NCI for the healthy future of ham radio !!! Join NCI @
    www.nocode.org

    By Anonymous Sion Chow Q. C. (9W2QC), at 12:47 AM  

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