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AO-27 is in a sun synchronous polar orbit, and is only operating during daylight hours. That means it will always rise in the northernly direction and set in the southerly direction, depending on the maximum elevation of the pass (that is, how high it appears in the sky). Generally, during the first 40% of a pass, AO-27 is vertically polarized and your antenna should be polarized as shown here. At this point, you will probably have the receive frequency set to 436.805 MHz with the squelch wide open for AO-27. If you are using an Arrow antenna, the long elements are the 2 meter elements, and they should be parallel to the ground at this point. About 25%-30% of the way through the pass, you can lower the frequency a step, to 436.800 MHz on most rigs. When practice, you'll know when to try this adjustment, as the signals from AO-27 will become a little harder to hear. It doesn't hurt to switch down a step and see if it helps, then switch back if not. |
| As the satellite approaches its highest point in the sky for a given pass, then you may find that the polarization will change. Rotate your antenna to get the best signal. You may need to make this adjustment more than once. By this time, you may have already set the frequency at 436.795, the approximate middle of the downlink frequency range. Soon, you will switch to 438.790, as just as when you hear the horn from a train as it goes by, the pitch changes very quickly as it passes in front of you. The pass when these pictures was only a 7° pass, talking from New York to California, so the antenna isn't pointing very high in the sky. If it were an overhead pass, at this time, the antenna would be pointing straight up and you might find it hard to figure out how much to rotate it to get the best signal. |
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As AO-27 heads south, you will probably notice it tends to be horizontally polarized. If you are using an antenna like this one in the picture, then where you point towards the horizon may be more critical, because its pattern is sharper horizontally. Those of you operating in the Northern American continent may start losing the Canadian stations and those further north, and may start picking up Mexico during transcontinental passes, and along the Weast Coast, perhaps Hawaii during Pacific passes. If you are using an Arrow antenna, and you will probably find that you get your best signal when the long 2 meter elements are perpendicular to the ground at this point. |
Depending on the time of year and your location, AO-27 may continue to give you signals until it gets close to the horizon, or it may suddenly turn into static. The latter happens because AO-27 has turned its transmitter off to conserve energy, since it shares power with the commercial satellite, EYESAT-1, which carries AO-27. There is nothing wrong with your radio or antenna if this happens, it's just that AO-27 is done with its power allocation for this pass. This is adjusted seasonally to make sure most of the Northern Hemisphere operators get a fair share of operating time on AO-27.
As the satellite gets close to the horizon, you may find that, in the same manner as when the satellite approaches its highest point in the sky, rotating your antenna somewhat may improve the signal. That is when the signal from AO-27 is spending the longest time in our atmosphere and when the effects of Faraday rotation are the greatest.
Also, during the latter half of an AO-27 pass over the North America, you may hear Spanish speaking stations who generally do not identify themselves. They do not realize that their supposedly short-range transmissions are being re-broadcast by satellite. Try to ignore them as best as you can until a diplomatic solution can be found for this problem. Meanwhile, realize that they are probably not running very much power, and a QRP station operating through an Arrow antenna or equivalent can often cut through the interference.
The other problem you may run into are stations repeatedly calling CQ on AO-27. Most of the time, people call CQ because they can't hear AO-27 and think that there's no one on. Experienced users of AO-27 will listen carefully to see if someone else has answered a CQ already, and if not, may respond to these stations once or twice. After these stations have been called and they have not answered, do not try to respond to stations calling CQ. At this point, they will almost certainly not hear you and you will be generating additional interference if you try to answer them. In generally, it is best for inexperienced operators to ignore such calls (unless AO-27 is unusually quiet), and leave stations with poor reception to the more advanced operators. A polite e-mail or post card explaining the problem is the best way to reply to such stations.
So, to avoid receiving such e-mail or post cards yourself, please make sure you can at least copy partial callsigns before transmitting to AO-27! Most operators on AO-27 are friendly and considerate people, and the more advanced operators often make special efforts to respond to newcomers and to help people get started.
73's and good luck!