Project Obelix

This article is intended to be a memo on the Obelix Project. Basically this is to materialize as a sun tracking radio telescope with the solar flux being fed to a public internet server for the benefit of radio amateurs and amateur scientists. The concept is still in the design and planning phase, but as you can see, the critical mechanical hardware already exists; this is a obsolete Inmarsat B terminal that has been decommissioned. Most fortunately this particular unit has never actually been to sea, rather it has stood on terra firma for evaluation and engineering purposes, thus being saved from the salinity and vibratory challenges the environment would have posed on board a sea-fairing vessel. The Obelix Solar Radio Telescope design implementation will the the B.Sc.(E.E.) engineering thesis subject of Mr. Pasi Suhonen.

Brief notes on Project Obelix:

• Dinosaur egg found (in Finnish) (19.05.2009)
• Picked up the fantastic piece of mechanical engineering and brought it home on a rental trailer (18.07.2010)
• Inmarsat B terminal on rental trailer in transit from Porvoo to Padasjoki (06.05.2010)
• Pasi for size (07.05.2010)
• Temporary location of pedestal base at place of development work (07.05.2010)
• View slightly further out, before elevating and balancing the pedestal mount (08.05.2010)
• Typical example of the Dicke front end (for prime focus) and back end processing unit (15.06.2010)
• Fitting even a compact Dicke switch at the dish focal point will be impossible; a more sensible solution would be to use Cassegrain illumination (18.07.2010)
• Feeding the dish from the rear would allow using a proper Dicke switch with a decent Thot termination (18.07.2010)
• A typical simple polarimeter (22.06.2010)
• View of the pedestal and gimbal mount for the two gyros (10.07.2010)
• Description of some of the main system modules before dismantling (20.04.2010)
• The dish pointing to Zenith (this will be one of the calibration points) (10.07.2010)
• Pasi measuring the feed focal point (10.07.2010)
• Example of total noise measurement using an X band horn demonstrator (cold sky) (18.07.2010)
• Example of total noise measurment (hot ground) (18.07.2010)
• Example of total noise measurement ("hot" foliage of a birch tree) (18.07.2010)
• Layout of hardware inside radome (for planning antenna modifications) (20.07.2010
• 230 Vac series wiring of Gyros (left Gyro) (20.07.2010)
• 230 Vac series wiring of Gyros (right Gyro) (20.07.2010)
• Gyros powered up fine: platform stabilized within some minutes of startup ! (10.07.2010
• Saturn Inmarsat B equipment by ABB NERA (Norway) (10.07.2010
• Pedestal by Seatel Inc. (10.07.2010)
• Radio equipment (SSPA, filter + LNA) by Hewlett Packard (10.07.2010)
• Big questions: frequency, dish/horn size/aperture, radome losses, Er/phase shift, conformity, beamwidth, rebalancing, heating etc. (20.07.2010)
• homebuilt gallows to aid manipulating the radome during development and service (30.06.2011)
• a different view of the gallows viewed from the North (30.06.2011)
• a ventilated durable cabinet will house the back-end electronics and server PC (28.07.2011)
• Euro sized 1 and 2 cards can be accomodated in the 19" rack installed in the cabinet (28.07.2011)
• further work during the second week of October, off with the radome ! (10.10.2011)
• locating suitable hardware for modifying the stepper drives took some months (10.10.2011)
• replacing the elevation 10-turn pot with the US Digital absolute encoder was pretty straight forward (10.10.2011)
• the original belt drive also used a ten-turn wirewould pot with a 54 tooth pulley (10.10.2011)
• using a longer belt and a large pulley (55 teeth), the azimuth encoder could be integrated (10.10.2011)
• this effort took some scaling in the US Digital encoder configuration however - we could simply could not locate a 54 tooth pully :-(
• now this here is an authentic IKEA Legitim 902.022.68 breadboard (no affiliation) sporting the prototype Arduino drive and the F1EHN controller w/ LCD (10.10.2011)
• a second Arduino will be launched to generate the Dicke Clock and also post process the rectified Thot/Tcold signals
• and another view of the prototyping breadboard for testing purposes (10.10.2011)
• Pasi and Pasi figuring out the ratio calculation of our 55 vs. 54 tooth pulleys (10.10.2011)
• another long day ending with sunset before any chance to calibrate against the sun, so we used the good old moon (10.10.2011)
• so now we got to out the initial calibration with Pasi & Pasi hard at work just before dusk (10.10.2011)
• we have the possibility to upgrade to X band with Dicke Switching, but for now the frequency plan/synthesis as of July/2011:
• Radio Astronomy Band (exclusive) 1660.5 MHz - 1668.4 MHz (7.9 MHz) - this is the band for observation of Galactic Hydroxyl emissions
• CF & predetection BW: 1664.440 MHz +- 2.5 MHz
• front-end hardware RF filtering will be added as found necessary (the closest near-band interferences source is less than 1 km away)
• 1. LO: 2147.328 MHz, synthesized
• 1. LO XTAL: 8.388 MHz
• 1. IF: 482.888 MHz +- 18 MHz
• 2. LO: 524.288 MHz, synthesized
• 2. LO XTAL: 4.096 MHz
• 2. IF: 41.4 MHz +- 2.5 MHz
• the front-end filter will be a six cavity LK Products 1.8 GHz filter modified for the 1665 MHz Radio Astronomy band, -3dB BW ~15 MHz, IL <1.8 dB
• for the LNA a two-stage GaAs FET 1.5 GHz band radio link front-end will be modified, retuned and rematched with stub notches added for GSM and UMTS
• here is a drawing (35k) of the model 23D stepper motor cabling at the antenna pedestal
• here is a drawing (51k) of the stepper motor control end at the Arduino controller being driven by the F1EHN tracking system
• for the record, the matching of the Seavey feed system, pretty optimal for 1665 MHz (10.10.2011)
• the mechanics look very promising and with microstepping of the model 32 motors and 0.1/0.05 degrees hysteresis in the F1EHN software worked great
• so we successfully tracked the Moon and also Cassiopeia, just for fun - only minor fine-tuning needed for perfection :-)

 

Updated Michael Fletcher 18.08.2019