The Twin Telescope Wettzell (TTW) Project is funded to be exec
uted during the period of 2008-2011. The design of the TTW was based on the VLBI2010 vision of the corresponding IVS Working Group. In the first two project years the design passed the simulations with respect to its specifications and was approved for production. At the Geodetic Observatory Wettzell a thorough soil analysis was made in order to define the sites for the towers of the new radio telescopes. Meanwhile the construction work has begun and acceptance tests of several telescope parts, e.g. azimuth bearings, took place. The full assembly of the radio telescopes is scheduled for the next two years. In parallel to the construction work at the Wettzell site, the design work for the different feed options progressed

Göldi, W

Hase, H

Klügel, T

Kronschnabl, G

Neidhardt, A

Pausch, K

English

ZENODO

PoS(10th EVN Symposium)092VLBI2010 - The TWIN radio telescope project atWettzell, GermanyG. Kronschnabl, T. Klügel, H. HaseBundesamt für Kartographie und Geodäsie, Geodätisches Observatorium WettzellSackenrieder Str. 25, D-93444 Bad Kötzting, GermanyA. Neidhardt∗Forschungseinrichtung Satellitengeodäsie, Technische Universität München,Geodätisches Observatorium WettzellSackenrieder Str. 25, D-93444 Bad Kötzting, GermanyK. PauschVertex Antennentechnik GmbHBaumstr. 46-50, D-47198 Duisburg, GermanyW. GöldiMirad Microwave AGHofstetstr. 6, CH-9300 Wittenbach, SwitzerlandThe Twin Telescope Wettzell (TTW) Project is funded to be executed during the period of 2008-2011. The design of the TTW was based on the VLBI2010 vision of the corresponding IVSWorking Group. In the first two project years the design passed the simulations with respect to itsspecifications and was approved for production. At the Geodetic Observatory Wettzell a thoroughsoil analysis was made in order to define the sites for the towers of the new radio telescopes.Meanwhile the construction work has begun and acceptance tests of several telescope parts, e.g.azimuth bearings, took place. The full assembly of the radio telescopes is scheduled for the nexttwo years. In parallel to the construction work at the Wettzell site, the design work for the differentfeed options progressed.The 10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation ofradio arraysSeptember 20th - 24th, 2010Manchester, UK∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/PoS(10th EVN Symposium)092TWIN radio telescope project Wettzell A. Neidhardt1. IntroductionOn the basis of the International VLBI Service (IVS) requirements for geodetic radio tele-scopes the Bundesamt für Kartographie und Geodäsie (BKG) has launched the TWIN project atWettzell (see [2]). Within this two rapidly moving radio telescopes are built, which will be equippedwith a broadband receiving system including the two geodetically used frequency bands S and X.Both telescopes have been designed for continuous operations over 24 hours 7 days per week. Asarray both telescopes can be additively interconnected, so that the effective receiving surface cor-responds approximately to that of the current 20m radio telescope at the Wettzell observatory. Theradial symmetric reflector concept combines the advantages of a dual offset antenna, as low noisetemperature, with the advantages of a Cassegrain or Gregory antenna regarding the mechanicalstability, the control possibility and the weight.The technical data of the telescopes are:- Diameter Main reflector: 13.2m- Diameter sub-reflector: 1.48m- Ring Focus Design with f/D = 0.29- Surface quality of the reflectors: < 0.2 mm RMS- Way length error : < 0.3 mm- Surface quality of the panel: < 0.065 mm RMS- ALMA mounting with angular velocities- Angular velocities of 12rˇ/s in azimuth and 6rˇ/s in elevation- Acceleration: Az/El = 3rˇ/ s2- Ranges of rotation: Azimuth 540rˇ, Elevation 0-115rˇ- Balanced outrigger- Excellent bearing- 27Bit Encoder: 0.0003rˇ resolution- Sub-reflector adjustable via a hexapod2. The ring focus designThe specially designed reflector uses a radial symmetric design. The advantage of this ringfocus antenna (see fig. 1) is a reflection of the rays from the outer main reflector regions into thecenter of the sub-reflector giving a better illumination of the feed horn. This design is properlysuited for broadband feed horns, which need a wider opening angle. Therefore the feed must bepositioned close to the sub-reflector, which is specially designed for such a setup.3. Structure optimizationThe TWIN radio telescopes were especially developed for geodetic applications. Thereforeit is essential to achieve extremely low deviations in path length between main reflector, phasecenter of the feed horn and axis intersection of the telescope (a path length error of 0.3 mm wasspecified!). Elaborate simulations using the Finite Element Method were performed to achieve a2PoS(10th EVN Symposium)092TWIN radio telescope project Wettzell A. NeidhardtFigure 1: The ring focus designvery torsion-resistant and solid supporting structure. All components from the main reflector tothe concrete tower were optimized for occurring load cases (wind, operating weight, temperature)to guarantee the required stability. Additionally the sub-reflector is positioned with a hexapod forgravity corrections.4. Microwave receiving systemsFigure 2: The proposed feed horns: a tri-band coaxial feed and the Eleven feedThe VLBI2010 concept designed a broadband receiving bandwidth of 2 - 14 GHz, with theoption to integrate the Ka-band (28 - 36 GHz). To realize these ideas new receiving systems haveto be developed, which will enable homogeneous illumination of the main reflector. They musthave a stable phase center and a system-noise temperature below 50 K.BKG has commissioned a tri-band feed horn (see 2 on the left side) that is able to work in thetwo geodetic frequency bands (S/X-Band), and also in the Ka band (see [1]). It will be possibleto participate in all standard VLBI and deep space network observations and to make a substantialcontribution to the improvement of the celestial reference frame in the Ka band.The Elevenfeed (see 2 on the right side) of Prof. Kildal (Chalmers University, Sweden)presently offers the best preconditions for the reception of a continuous frequency range of 2 to3PoS(10th EVN Symposium)092TWIN radio telescope project Wettzell A. Neidhardt14 GHz (see [3]). Extensive simulations showed good performance of the feed up to ca. 10 GHz.From 10 - 14 GHz the performance is also suitable. The ohmic attenuation of the copper lines andthe differential outputs pose some problems. To solve them cryogenic cooling as well as severalspecial low-noise-amplifiers are necessary.The microwave converter is designed for four 1 GHz broad frequency bands, which then canbe recorded with digital data recording systems. Because of the broadband receiving, which coversapproximately three octaves, two frequency converters are required.5. Locations of the new telescopesFor the location decision for the two TWIN telescopes extensive soil specimens and geologicalsurveys were done. The goal was to find two locations for the two telescopes which offer as goodgeological stability as the 20m radio telescope. This has an extraordinarily low azimuth axis de-viation. In total more than 12 drillings were made to determine the geological conditions. Specialattention was turned to set the height of the elevation axis onto the same level for an additionalsystem monitoring. A suitable location was found close to the observatory, which simplifies theconnection of the new telescopes according to the local survey, the infrastructure and the opera-tional tasks.Figure 3: The new sky line of the Geodetic Observatory Wettzell: in the background are the new TWINtelescopes6. Control and operationsBoth telescopes have been designed for continuous operations over 24 hours 7 days per week.Therefore special attention was turned to the control concept and the servo system. All componentswere designed for high availability, precise tracking and 1000 source observations per day. Follow-ing this strategy continuous geodetic time series can be generated with higher accuracy. Especiallythe increased number of sources and an efficient observation improves the tropospheric corrections.According to this new observation strategies must be developed where the telescopes can operate4PoS(10th EVN Symposium)092TWIN radio telescope project Wettzell A. Neidhardtparallel on different sources, additiv on the same sources or in single telescope mode, to maintainthe non-operative one.Other new techniques will allow to increase the e-VLBI sessions and to run the observationswith remote control or completely unattended. The new operational building is designed to allowsuch new control modes. It offers possibilities for local fringe test and zero baseline correlators aswell as the connectivity and control room to run different sites from there. This is very importantfor the operations of the telescopes at the Transpotable Integrated Geodetic Observatory (TIGO)in Concepción, Chile and at the German Antarctic Receiving Station (GARS) O’Higgins, whichare operated by personnel stuff of Wettzell. To realize such remote control scenarios the e-controlsoftware will be used, which is developed by a team of the observatory[4].7. Summary and outlookOverall the described setup is the first complete and rigorous realization of the visions ofVLBI2010 (see [5]). The telescopes are in the final construction phase. All of the high frequencycomponents are commissioned and are under construction now. The digital broad band acquisitionsystem is under test. The new antennas will be tested for operations in the year 2011. Colocatedwith the existing 20m radio telescope and with the other instruments for space geodesy the newproject is a pathfinder technology for the new proposed stations within the Global Geodetic Ob-serving System (GGOS).References[1] W. Göldi, Evaluation of Suitable Feed Systems, IVS VLBI 2010 Workshop on Future RadioFrequencies and Feeds,http://www.fs.wettzell.de/veranstaltungen/vlbi/frff2009/Part3/10-Goeldi_Workshop21.pdf (2009).[2] H. Hase, R. Dassing, T. Klügel, G. Konschnabl, A. Neidhardt, P. Lauber, R. Kilger, K. Pausch, TwinTelescope Wettzell (TTW) - A VLBI2010 project, IVS VLBI 2010 Workshop on Future RadioFrequencies and Feeds,http://www.fs.wettzell.de/veranstaltungen/vlbi/frff2009/Part8/ttwvlbi2010e.pdf (2009).[3] P.-S. Kildal, Characterization of Feeds for Radio Telescopes, IVS VLBI 2010 Workshop on FutureRadio Frequencies and Feeds,http://www.fs.wettzell.de/veranstaltungen/vlbi/frff2009/Part3/00-Tutorial-Wettzel-Kildal-090317cr.pdf (2009).[4] A. Neidhardt, M. Ettl, C. Plötz, M. Mühlbauer, R. Dassing, H. Hase, S. Sobarzo, C. Herrera, W. Alef,H. Rottmann, e-control: new concepts for remote control of VLBI-telescopes and first experiences atWettzell, The 8th International e-VLBI Workshop, EXPReS09, PoS(EXPReS09)038 (2009).[5] Niell, Arthur, et. al., IVS Memorandum 2006-008v01. "VLBI2010: Current and Future Requirementsfor Geodetic VLBI Systems",http://ivscc.gsfc.nasa.gov/publications/memos/index.html (Sept. 2004).5

Characterization of Feeds for Radio Telescopes,

e-control: new concepts for remote control of VLBI-telescopes and first experiences at Wettzell,

Evaluation of Suitable Feed Systems,

IVS Memorandum 2006-008v01. &quot;VLBI2010: Current and Future Requirements for Geodetic VLBI Systems&quot;,

VLBI2010 - The TWIN radio telescope project at Wettzell, Germany

https://zenodo.org/record/7036/files/10th%20EVN%20Symposium_092.pdf

VLBI2010 - The TWIN radio telescope project at Wettzell, Germany

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