Tracking Oko from Sweden

To track the Russian Oko missile-warning satellites (see sketch on the right) on S-band is no big feat but for me it was great, after 40 years of satellite monitoring, to finally track a satellite on S-band. Oko satellites transmit strong CW signals on 2286, 2292, 2298 and 2304 MHz. These satellites move in "Molniya" orbits, the elliptical orbits with about 12 hours period and apogee over Asia or North America. The Asian loop apogee can be seen at 75-80 degrees elevation from Sweden and the satellite moves very slowly. In this way a fixed antenna direction can be used for long periods. Hopefully, this little account can encourage more enthusiasts to try this.

I have put together a setup using an Airlink 60 antenna designed for WLAN frequencies that also works on 2200-2300 MHz. It is linearly polarized, so the gain when picking up circulalrly polarized signals is 3 dB less, i.e. about 19 dB. Its beamwidth is about 14 degrees. The antenna is followed by a SSB Electronic SLN series pre-amp. The signal is then fed into a downconverter that I bought from SSB Electronic several years ago, but have never really found use for. It converts 2200-2300 MHz to 600-700 MHz. I tuned the intermediate frequency with my Alinco DJ-X10 in the CW mode.

On 25 August 2006 I listened for Kosmos 2393 at 1005-1048 UT as the satellite had started to come down from apogee which occurred at 0940 UT. The range during reception varied from 39876 km and 38700 km. Elevation angle  was almost constant at 76 degrees, while azimuth changed 15 degrees, which does not require much antenna movement at this very high elevation angle. Signals were strong on 2298 and 2304 MHz. I had some local interfernce on 2304 MHz (harmonics or  external sources) so I concentrated on 2298 MHz. Clearly, my receiving setup is subject to drift and I suspect the local oscillator of the downconverter. Nevertheless, doppler shift was evident. The CW carrier was very strong ( I had 5 bars on the S-meter), and clearly showed on the little spectrum display of the Alinco.