SK6OSO

July 18-19, 2009

EME operation from Onsala Space Observatory has been done in the past. Already during the 90's, the old 25.6 meter dish was put into EME operation with the call sign SK6WM (OSO EME Group). That operation was an initiative by SM6FHZ and SM6EBM (SK), and they used 13cm.

This spring, the idea came up once again, but this time it was the 23cm band that was to be activated. We also decided to apply for a special callsign, SK6OSO.

The 25.6 meter antenna at Onsala Space Observatory was built in the 70's for the "Scandinavian Tele Satellite Committee", a joint operation between the three Nordic countries. The experiments conducted at that time were a preparation for the Tanum Satellite Station which was operated by the Scandinavian telecommunication authorities.

After the STC experiments, the antenna has been used for astronomical studies by Chalmers University of Technology. It was designed for frequencies ranging from some 800 MHz to about 7 GHz, although with limited efficiency at the band edges.

As the radio astronomers interest moved on to higher frequencies, a new 20 meter millimeter wave telescope was built nearby in 1976 and the old antenna was largely used for student labs.

Following an increasing interest by the geophysical community about the tectonic plates' drift, there was a renewed interest in VLBI measurements. An activity that is reoccurring and which can make use of lower frequencies, the old antenna has found new use. A complete refurbishing of the antenna controller electronics was made 1996. The old Maser low noise amplifiers were replaced with modern cryogenically cooled FET amplifiers for L- and C-band.

The antenna is today used almost all year around, except for a short brake in the summer during which the equipment is serviced and checked by the observatory's engineering staff.

It was during one of these week-ends that we were granted use of the antenna for EME by kind permission from the director, Prof. Hans Olofsson

Since the majority of all astronomical observations make use of both left- and right-hand polarization, and since OSO uses the L-band, there was already a feeder available. The astronomic receiver was down for maintenance and hence, its cradle could be used to fit the transverter equipment.

A suitable (well...) transverter was SSB Electronics LT23-S. It was modified for rack mount, had separate TX and RX paths, extra relay installed and all connectors placed on the front panel. One problem with the transverter was the drifting LO. There are a number of good crystal oscillator designs available, none of which the designer chose. The LO is "subject to redesign".

A modified GSM base station LNA was obtained from Per, SM0DFP, and a bunch of "TUG" (Power Amplifier) modules from Hannes, SM6PGP. All this was placed in a small rack cabinet of 8HE.

The rack slipped perfectly through the narrow neck of the service tunnel and on to the control room behind the focus of the telescope.

In the meantime, the operation center was established in the old control building, nowadays used as a museum only. Luckily, all cable interconnections still takes place there, and we were able to connect to the coax cables for IF (144MHz) and to some of the unused signal cables for RX/TX control.

The software control system of the antenna can be remotely operated via TCP/IP. Hence the Antenna Control could be moved from the main building down to the museum. The system has a number of tables for different celestial objects such as known radio sources used for calibration, a table for the planets of our solar systems and our moon.

The system was rebuilt/recompiled using new hardware in the spring of 2009. Unfortunately, the planetoid table with the moon was not verified. This caused us major worries, as we could hear Ingolf, SM6FHZ, located only a few kilometers away getting good echoes while we heard nothing at all.

It was then realized that maybe the system did not track the moon. Björn, SM6CSO, downloaded amateur tracking software, and by using its output data we came to the conclusion that the controller software table was incorrect. After switching to manual control we got really nice echoes. The disadvantage was that someone had to sit at the control computer and manually enter coordinates once every minute...

Except for the problem with the antenna steering, the system took less than 3 hours to set-up. We were active during major parts of the time when the moon was up, except for some time during the nights when European activity was low. Radio amateurs also need to sleep.

During the week-end, we were able to make successful contacts with about 50 stations all over the world, including perhaps the worlds' shortest (in terms of distance) QSO with Ingolf-FHZ. Mode was high speed barred CW (Send a sign, wait for echo, send next, wait for echo etc). This because the key clicks from both stations desensitized the equipment. We established the contact when both stations had their antennas in a 90 degree angle, minimizing RF leakage.

On Sunday the operation was terminated, after having worked just every EME capable station we could find on the HB9Q chat. We made contacts with all continents except Africa (no one active) and South America (although we were heard in Argentina).



73 de Ulf, SM6GXV