Sunday, April 11, 2010

Swans and Satellites

I love mornings and its a rare day that I am not on the road at sunrise somewhere in Southern Alberta. On any one of these mornings, you will find me checking in with the breakfast club on AO51. The breakfast club is a small group of guy's spread across Canada and the US that check in on AO51 as this satellite rises over the pole from the north. This morning finds me parked near a wetlands just east of Calgary where I have positioned myself to shoot photos of the Tundra Swans that had been sleeping near the shoreline upon my arrival. I had set a alarm on the tracking program that I use for predicting satellite orbits, and was confident that I would not miss the arrival of my favorite satellite - AO51 from the north. On most mornings I am the first Ham to wake it up as it rises over my horizon. Shortly there-after, John-K8YSE comes on board from Cleveland in Ohio, although on occasion I am surprised by unexpected visitors. Lately that was Reid - OX/N0RC from Thule Air Base in Greenland, who caught me off guard as this was the first time that I worked Greenland on satellite. Soon thereafter Leo-W7JPI checks in from near Tucson Arizona, and on it goes. AO51 orbits 800km above the earth in a sun-synchronous orbit at speeds of about 28,000 kph. AO51 orbits the earth about every 90 minutes, so I can expect there to be 2 to 4 good 15 minute passes over my location every day. Because of the extreme speed and distances there is an effect called doppler shift. It is a similar effect to listening to a car approaching your location along a highway. The sound waves from the car are compressed as the car gets closer (high in frequency) and stretched (lower in frequency) as the car passes and goes further away. It is the same when listening the the leo satellites. For example when listening for AO-51, the downlink frequency being transmitted from the satellite is 435.300 MHz, on arrival (AOS) it will first be received on 435.310 MHz when AO-51 is 3000 kilometers away. When the satellite is overhead at about 800 kilometers (90 degrees) there is no doppler effect and the transmitted frequency is 435.300 MHz When the satellite departs (LOS) the frequency will begin to decrease until the received frequency is at 435.290 MHz. So there is a total shift in received signal of 20 KHz. These frequencies will have to be either programmed into your transceiver or receiver or manually adjusted during the pass as I do. On 145 MHz the Doppler is only about 3.8 KHz, so these is little need to make any adjustments for the uplink. Working the other leo's orbiting the earth is similar to what I have just described.
I know I have talked about how much I love mornings - early mornings that is, and its all about the wonderful light on the eastern plains of southern Alberta. The art of photography is often referred to as "painting with light." This expression takes on a very special meaning for the outdoor photographs made during the early morning hours just after sunrise, such as on this morning. Shooting during these hours affords you opportunities for using various view points in relationship to the sun's position to define the subject in a creative manner. When the atmospheric conditions are right, the morning light creates a certain glow. The contrast in the scene falls off very rapidly with distance thus making the background soft and receding in the distance, giving the whole scene an ethereal quality and a feeling of depth.
I had been so engrossed in shooting photos of swans, I was startled when the alarm of my satellite tracking program gave the one minute warning that AO51 was due over the horizon. With my headphones in place, I pointed my downlink antenna north and within a few minutes, I was working guy's south of me in Montana, Utah, Nevada, and Arizona as well as Jose-XE2BHL from his home in Mexico. The duration of the pass from AOS (acquisition of signal) to LOS (loss of signal) was approx 15 minutes. Once the pass was over, and with one last look at the swans who by now had waken up and were feeding, I headed south on the 797 towards Langdon where I would make a stop for coffee before heading home on a beautiful southern Alberta morning.

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