circle 168 on reader service card

How to get on OSCAR 22 with an HT.

by John A. Hansen WA0PTV

Ken KE2SR, who lives near Buffalo, New York, is a fairly new Technician class ham who uses his Commodore 64, a Digicom modem, and an HT lo communicate on packet radio with hams in Australia, New Zealand and elsewhere around the world via the orbiting satellite OSCAR 22, Impossible, you say? Not at all—he simply uses his local packet satellite gateway node.

The satellite gateway node system is a fairly new development in packet radio satellites. It pennifs region-wide access by hams with anything from very modest equipEiicnt to the latest in digital satellite technology, You don't need a satellite transceiver, you don't need satellite antennas, and you don't need any specialized modems, All you need is a standard bare-bones packet station that is capabic of connecting with your local BBS, The "catch" is that there must be a BBS in your area equipped as a satellite gateway node.

The satellite gateway node software automates the interface between a standard packet radio bulletin board system and a high speed (9600 baud) satellite ground station. All users of the BBS (and all other BBSs in the region) can have access to directories of the files available on OSCAR 22, can mark files to be downloaded the next time tiie satellite is overliead and have those files imported directly into the BBS, and can upload files io the satellite. In shorlT they can do virtually everything with tiie OSCAR 22 satellite that they would be able to do if they spent several kilobucks setting up their own satellite ground stations,

About OSCAR 22

UoSat-OSCAR 22 has been in orbit more than a year now. It was built by the University of Surrey in England and represents the current state of the art in digital satellites. It is essentially an orbiting bulletin board with 8 megabytes of on-board storage. Tiie uplink is on 2 meters and the downlink is on 70 em. Both the uplink and the downlink are FM and run at 9600 baud. Files can be uploaded and received at a very fast rate.

It is possible, for example, to upload a 100K file in about three minutes. Depending on the level of congestion on the satellite, it is possible to receive files from the satellite at about the same rate. On a typical satellite pass of 13 minutes duration, over half a megabyte of data can be obtained. For the most part this data is compressed, so the amount of actual uncompressed data received is quite a bit greater.

Typically, OSCAR 22 passes over any point in the United States six times per day, with three passes in the morning and three passes in the evening. The passes are about 10 to 15 minutes in duration and are spaced about an hour and a half apart. Because of the high data rates used on OSCAR 22, the variety of material available on this satellite is much greaier than on a standard terrestrial BBS. In addition to messages between individual hams, there are photographic images taken by the on-board camera; public domain software packages; schematic diagrams; digitized images of hams, their stations and the areas where they live; and digitized voice files. There has been something of an explosion of dig ital experimentation on this bird as people have begun to appreciate the implications of being able to easily transfer files that arc measured in hundreds of kilobytes rather than in bytes or kilobytes.

Ground Station Requirements

Ground station requirements arc fairly modest, requiring FM radios on 2 meters and 70 cm and vertical antennas with a pieamp on the 70 cm side. As a practical matter, however, most ground stations access this satellite with OSCAR-13-class stations (high gain, directional antennas) so that in heavily populated parts of the earth, such as the United States, access with vertical antennas is difficult. There are a few other difficulties as well. The radios used must be capable of 9600 baud transmission/reception and the TNC used must have a 9600 baud modem. Because the satellite moves across the skyT there is a problem tuning the radio during the pass to correct for the Doppler shift. The technology is available for automatically tuning the radio and pointing the antennas, but it is difficult to accomplish this cheaply.

Satellite tracking software w ill let you know when the satellite is within range.

73 Amateur Radio Today March, 1993 19

0 0

Post a comment