This document should be considered a WIP (Work In Progress). In reaction to many
questions regarding how to work the easy sats, this effort was born.
Mike Gilchrist, KF4FDJ -- February 28, 2000 -- Fort Myers, FL
THE ACTIVE BIRDS
Now that MIR is silent, there are currently 4 satellites that fit the category of easy sats. FO-29, when in digitalker mode, AO-27, for daylight passes over the Northern Hemisphere, SO-35, or SUNSAT, when the operators turn the device on, which is usually weekend daylight passes over Europe and North America, and UO-14, which is usable during all passes visible to the operator.
The FO-29 digitalker transmits on a frequency in the 70-cm band.
AO-27 is a mode J FM bird. Mode J is 2-meters up, and 70-cm down.
SO-35 is also an FM bird, and is usually operated in mode B, but can also be operated in mode J. Mode B is 70-cm up and 2-meters down.
UO-14 was launched as a digital workhorse. It managed to carry digital traffic half way around the world for medical staff working in communication challenged third world countries. The torch, and duties were passed to UO-22. Since that time, the bird has been sending telemetry, until February, 2000, when the control operators toggled the bird to mode J FM.
WHEN AND WHERE TO POINT
Since all these birds are low earth orbit satellites, most passes will be between 6 and 18 minutes in duration. Timing is critical in working any amateur satellite.
Since these birds are all considered weak signal, you must know when the satellite will pass over your location, and where in the sky to point your antenna. 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:
I believe WINORBIT 3.6 is one of the better programs available for beginners using PC type computers. Mac users should look at MacDoppler, available from the AMSAT site, or from the developers site:
Both of these programs have proven to be Y2K compliant, and load 2000 Keplerian coordinates with no problem.
Be sure to download the latest Keplerian coordinates if you download a tracking program. Each prediction program needs these coordinates to determine where the satellites are, and to help you determine when the satellite will be over your horizon. Another casual approach, is to use an online prediction site, such as:
This site will generate pass predictions for a selected satellite. Be aware, that as of the time this article was written, this site is using stale Keplerian coordinates, and might not give absolutely correct positions for the satellites. They might be off by close to a minute. If I encounter a similar site with more up to date coordinates, I will modify this text accordingly.
THE DOPPLER EFFECT
Since LEO (Low Earth Orbit) satellites travel at high velocity, radio signals arriving at and moving away from the satellite are subject to a perceived change in frequency. This phenomenon is called Doppler shift.
Much as a passing car with horn blaring will seem to change pitch the moment it passes an observer, satellite communications are subject to the same effects. While listening to a signal from a satellite that is approaching your position, you will receive the signal slightly higher than the actual transmitted signal. As the satellite moves away from you, the
received signal will be found lower in frequency than the actual transmitted frequency.
The opposite effect is seen on an uplink signal to a satellite. If the bird is approaching you, your transmit frequency will be slightly lower than the frequency the satellite receiver hears. Likewise, as a bird recedes from your position, you will need to transmit higher in frequency to compensate for the Doppler effect.
Doppler shift is more pronounced the higher the transmitted frequency. As a rule of thumb on the LEOs, the maximum 2-meter Doppler shift is around 3.5 kHz, while on 70-cm, it may be close to 10 kHz.
The Doppler frequency shift is most pronounced as the satellite makes closest approach to your position and then moves away. Passes low on the horizon will have less Doppler shift than a pass closer to your zenith.
Most readers of this document will be using a handheld scanner or an HT to listen to, or work the easy sats. Since these devices are generally only capable of being tuned in 5 kHz increments, you will have to program a series of frequencies into your rig. Under each section for a particular bird, I have included a list of frequencies tabulated, mindful of this
LISTENING TO THE FO29 DIGITALKER
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 the BB for a mode schedule and other details.
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.
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.
If you are using a handheld device, 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!
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
Here are the frequencies you should program into your rig:
435.910 Mid Pass
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 kid, 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.
As previously stated, Oscar 27 is a mode J satellite. Your uplink needs to be a low power 2-meter signal. AO27 is at times a difficult bird to hear. You will need 70-cm FM receive capability. Many operators use a dual band HT to work this bird.
A gain antenna for 70-cm is usually required; a stock rubber ducky will not be adequate. I have had limited success with a long, wispy dual band cat whisker type gain antenna. If you use a car body or another piece of metal as a reflector, you will increase your chances of working the bird. In any event, whichever antenna you use will have to be rotated to best match the polarity of the bird. Experience shows a vertical orientation at the beginning of the pass, to nearly horizontal mid pass works best.
AO27 is a polar orbiting satellite, meaning the orbit of the bird takes it nearly over
both the South and North Poles. Software controls the amateur radio payload, which toggle
the satellite on during passes from north to south, and only during daylight passes. The
satellite turns on several minutes after entering daylight, and stays on for another
minutes. Because of these limitations, the bird is only usable by operators in the Northern Hemisphere, and those close to the equator -- ONLY during daylight passes.
Operators should understand that this satellite is seldom vacant, and if you cant hear it, DONT transmit. You will only cause QRM to other operators, and sully your reputation. AO27 has a very sensitive receiver, and I have managed to hit it with 100 mw of power at times.
Since AO27 is a very busy satellite, especially on holidays and weekends, a portable operator will most likely have limited success, unless they use a multi-element gain antenna for the uplink and downlink. I have also found use of a preamplifier beneficial for hearing the bird well, and knowing when to jump in for a contact.
Most QSOs are short, contest style exchanges, including grid square, first name, and city. This sort of contact maximizes use of the bird for the scores of operators who might be trying. Weekend passes, to the uninitiated, sound a bit chaotic. There is a culture, which exists on the bird, and my best advice is to listen to a couple passes, and model your operation after the successful operators you hear.
AO27 is a full duplex bird, meaning that you can listen to the downlink as you transmit. If your rig is capable of full duplex operation, fine, otherwise half-duplex operation works just fine on the FM birds if you program the frequencies in your HT correctly.
You should program your HT with 5 frequency pairs for working AO-27. Start with the first pair, using a non-standard split, and tune to the next one as the pass progresses.
Downlnk - Uplink
436.805 - 145.845
436.800 - 145.850
436.795 - 145.850 Mid Pass
436.790 - 145.850
436.785 - 145.855
The Doppler shift on the 70-cm downlink can be a little more than 10 kHz. The 2-meter Doppler is close to 3 kHz.
I seldom need to use the 5th pair, except on high passes, and only when the TEPR keeps the bird on so far south like it is operating presently!
WORKING SO35 - SUNSAT
SO35 typically operates in a mode opposite AO27 -- mode B as opposed to mode J. Mode B is 70-cm up and 2-meters down. While the 2-meter uplink Doppler correction on mode J is not terribly critical, you must compensate for Doppler on the 70-cm uplink while using this bird. The Doppler correction on this bird is counter-intuitive, if you are used to working a
mode J bird. Doppler shift on the 70-cm uplink is roughly 3 times as great as the 2-meter Doppler shift. Maximum Doppler shift on the 70-cm uplink can be a little over 9 kHz! If you DON'T tune the uplink, you probably WON'T be one of the successful operators.
While the downlink on AO27 is hard to hear, SUNSAT has a very strong downlink signal, and is receivable with a standard rubber ducky antenna atop a handheld scanner or HT. The bird also seems to have a very sensitive receiver, so low power HTs will work the bird if conditions allow.
Since this satellite has been usable only a few times, and is active only on weekend daylight passes; it is a very popular bird when active. As with all FM receivers or repeaters, the satellite is captured by the strongest signal. As a portable operator, you might have only limited success working this bird, although you should be quite successful receiving signals from the satellite.
As with AO27, short contest style contacts help facilitate more users during a pass. Common sense and courtesy must prevail. As with any amateur communication, use the minimum power necessary to complete the contact.
If your rig is capable of tuning small increments, use this table as a guide. Tune the downlink until your discriminator meter, or S meter shows you are tuned to the correct downlink frequency. Look across the table and make certain your transmit frequency is close to the associated 70-cm table entry.
Downlink -- Uplink
145.825 436.291 Satellite directly east or west of you
If you are using a scanner to listen, or an HT which only tunes in 5 kHz increments, use this table as a guide. Since the downlink frequency will be closest to 145.825 during most of the pass, break the pass into a little over 3 minute chunks, and increment your programmed pairs (you will need to program nonstandard splits) during the pass for best centering in the
passband of your uplink signal.
Downlink -- Uplink
145.825 436.290 Satellite directly east or west of you
The first or last pair may not be required, depending on your latitude.
To determine the latest operating schedule and mode (if it changes) for SO35, check out the SUNSAT website:
UO-14 is currently operating as an FM bent pipe "repeater" satellite. As such, it is a full duplex bird, meaning that you can listen to the downlink as you transmit. If your rig is capable of full duplex operation, fine, otherwise half-duplex operation works just fine on the FM birds if you program the frequencies in your HT correctly.
UO-14 is functionally similar to AO-27, but is available during all passes visible tot he operator. The transmitter is a little more powerful than AO-27, so antenna gain and orientation do not seem to be as critical.
I can hear UO-14, using an HT, in the middle of my one story ranch home. Working the bird, at the time of this writing is difficult at QRP levels. Due to the popularity of the bird, and perhaps because it is new, this bird is very active. Until the activity subsides, working this bird as a low power operator will surely test your abilities.
You should program your HT with 5 frequency pairs for working UO-14. Start with the first pair, using a non-standard split, and tune to the next one as the pass progresses.
Downlnk - Uplink
435.080 - 145.970 AOS
435.075 - 145.975
435.070 - 145.975 Mid Pass
435.065 - 145.975
435.060 - 145.980 LOS
As with the other FM birds, if the satellite is busy, limit both the quantity and duration of your QSOs. All users should view the amateur satellite fleet as a shared resource, and strive to develop considerate operating practices.
One of my favorite web sites to send an inquiring person for a visit is:
A great place for kids to learn about space science is:
Another site which all teachers, scout leaders, or any other person wanting to bring the world of space science to others should bookmark is:
An excellent web site, maintained by Jerry, K5OE, is:
Jerry has designed and documented some very nice antennas, capable of working the LEOs. Most of his projects can be built for low cost, using materials from a home improvement store.
PROCEDURES FOR THE SUCCESSFUL OPERATOR
Here are some parting thoughts on how to help ensure you will be a successful operator on the easy sats. As with all things in life, careful planning, thoughtful attention to your skills, and a friendly style will help assure you of many hours of satisfying satellite operation.
1) Operators who only put their call out are seldom picked out of the crowd and engaged in a QSO. Instead, pick a station and call them specifically. Try to time your transmission so you jump right in when the last QSO clears.
2) Rehearse what you're going to say. When the bird is yours, speak loudly, clearly, and to the point. Excess "umm, ahh, well, ah" transmissions will only cause other operators to ignore you, especially on a busy bird.
3) Don't call CQ. If there is at least one other operator out there, they will hear you. Reserve calling CQ for the linear birds where one must hunt up and down the transponder for a signal. If you are calling CQ, most operators assume you can't hear the bird.
4) Use email and posts to the BB as an effective means to increase your chances. Pick a regular, and send them an email. You might want to tell them you are going to be QRP portable on AO27, SO-35 or UO14 the second pass tomorrow, and ask then to listen for you. Many times such a technique will open the door, and other operators who have heard your call and grid will call you as well.
Usually, when an operator posts they are going to be working a special events stations, or a rare grid, or from a unique operating position, they generate traffic. Try announcing you will be working mass transit portable. :-)
5) Use a gain antenna, properly oriented and pointed at the satellite. Move around and optimize your position. Many times unseen elements affect the antenna pattern, and moving a few feet makes all the difference.
6) Invest in a preamplifier. Many times it makes the difference between being able to work the bird or not. If you can't hear it, you can't work it! (see #3)
7) Be polite and thank the other operator for the QSO. Nice guys DO win, and will be given a second chance.
8) If another operator calls a station, and you hear them, wait a second before "grabbing" the bird. If you jump in too soon, you will acquire a bad reputation and other operators will avoid you.
I think many times the case is an operator does NOT hear the initial call, instead of a callous disregard for decorum, which stems from having a poor downlink. (see #6) There are several frustrated operators out there who fit this model, and believe me, they ARE ignored. There IS a culture on the easy sats, and a little time spent monitoring and learning this culture will be time well spent.
9) Don't whine. If you whine on the sigs or bulletin boards, or on the satellites, you might acquire a bad reputation and other operators will avoid you. If someone else tries to engage you in negativism here or on the birds, dismiss them. Do not enter into negative dialog, period. Generally negativism comes from failure. Encourage them to improve their lot, and become a winner.
So, the well equipped operator, who is polite, persistent, speaks clearly, and gets to the point is the operator who will have most success as a portable satellite operator.
73, and think positively - Mike
If you have any comments, additions, or modifications to this document, please contact me directly. We will attempt to post the latest version of this document monthly.
This document is copyright © 1999 by Michael J. Gilchrist and may not be reprinted in part or whole without permission from the author.
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