Satgen 523 Tracking Sats Heard 2 by GM4IHJ (BID SGEN523) 1999-04-03 Constellations of Low Earth Orbit LEOsats have been around for some time. The Russian "follow my leader " military comsats set the scene more than ten years ago. But the advent of fleets of LEO commercial sats ( 120+ to date from OrbCom, Iridium , and more recently the gradual build up of Globalstar numbers) , has introduced a new situation whereby 3 or 4 satellites from the same fleet can be in your sky at one time. What tactics can be used to sort them out, and would these procedures work if amateur radio got organised globally, and gradually launched a fleet of small voice QSO comsats , as suggested in a recent AMSAT Journal ? As opposed that is, to the steady but unregulated flow of disparate amsats which presently do not blend with one another and which cannot offer regular effective sat to sat connection. These thoughts arose after initial frustration trying to discover why Iridium over Europe has not exactly got off to a good start. Eg - are the Iridium sats able to pass a call seamlessly from one sat to another ? The solution came via the FFTDSP display . With integration set to give 9 or 10 minutes of display time , enough screen is available to show the succession of in range satellites. With individual satellites being clearly distinguished by their very different doppler traces. On these doppler curves the individual Ddot ( Doppler rate) plainly reveals the real time nature of each satellites orbit , with respect to your station. With the sat about to leave your footprint showing a slowly declining Ddot. While the next in line in that orbit plane is showing a steady increase in Ddot, whilst out at some remove from your station ( if above 40 deg lat), fleet members in adjacent orbit planes are showing the slow steady Ddot tracks of satellites at long range. When satellite ground station controllers are adding to the confusion by switching off their uplinks ( and hence transponded downlinks) , the situation is obvious on the FFT display, even when, as happens now and then, one satellite signal is crossing another or over lying it on the display. So that at times the display resembles a Scottish morning sky as homeward bound Scandinavian, German and Eastern European jets coming from America , spread vapour trails from horizon to horizon. But unlike the aircraft trails which blow away. The FFT display can be examined in real time , or it can be copy printed and used later as a guide to understanding what is happening. As when the switching of signals can be used to work out where the ground stations are located by noting where/when in your footprint their activities are apparent and, where they are not. Plus, what makes this all the more instructive, is the way it indicates that as yet , all has not gone well for the commercial LEO ventures. Looking back to a year or two to when the Little LEO consortium were suggesting a complete take over of the amateur VHF/UHF bands. It would be interesting to eavesdrop on their present deliberations, as they note the slow progress of the front runners.