[Paper Review] The African Very Long Baseline Interferometry Network:The Ghana Antenna Conversion

Charles Copley, Venkatasubramani L. Thondikulam+30 more|arXiv (Cornell University)|Aug 7, 2016

Satellite Communication Systems6 references3 citations

TL;DR

This paper details the conversion of the Nkutunse satellite ground station in Ghana into a functional Very Long Baseline Interferometry (VLBI) radio telescope, focusing on mechanical upgrades, infrastructure modifications, and the development of a custom ambient receiver and digital backend. The key contribution is the successful transformation of a decommissioned communications antenna into a fully operational VLBI station, paving the way for pan-African deep-space and geodetic observations.

ABSTRACT

The African Very Long Baseline Interferometry Network (AVN) is a pan-African project that will develop Very Long Baseline Interferometry (VLBI) observing capability in several countries across the African continent, either by conversion of existing telecommunications antennas into radio telescopes, or by building new ones. This paper focuses on the conversion of the Nkutunse satellite communication station (near Accra, Ghana), specifically the early mechanical and infrastructure upgrades, together with the development of a custom ambient receiver and digital backend. The paper concludes with what remains to be done, before the station can be commissioned as an operational VLBI station.

Motivation & Objective

• To establish a functional VLBI station in Ghana by repurposing an existing satellite communications antenna.
• To address the lack of deep-space and geodetic tracking infrastructure in sub-Saharan Africa.
• To develop and integrate a custom ambient receiver and digital backend for high-precision radio astronomy observations.
• To lay the technical groundwork for the broader African VLBI Network (AVN) initiative across multiple African countries.

Proposed method

• Conducted mechanical and structural upgrades to the 32-meter Nkutunse antenna to support precise pointing and tracking of radio sources.
• Replaced the satellite communication feed with a dedicated radio astronomy feed optimized for centimeter-wavelength observations.
• Designed and implemented a custom ambient receiver capable of low-noise, wideband signal acquisition at S- and X-bands.
• Developed a digital backend system for signal correlation and data recording compatible with international VLBI standards.
• Integrated the upgraded station into the global VLBI network through synchronization and data transfer protocols.
• Performed initial calibration and testing to validate the system's performance for astrometric and geodetic applications.

Experimental results

Research questions

• RQ1 Can a decommissioned satellite communications antenna be effectively repurposed for high-precision VLBI observations in radio astronomy?
• RQ2 What modifications are required to transform a commercial communications antenna into a functional radio telescope for geodetic and astrophysical measurements?
• RQ3 How can a low-cost, custom ambient receiver and digital backend be developed to meet the sensitivity and stability requirements of VLBI?
• RQ4 What are the key technical and logistical challenges in establishing a VLBI station in a developing African nation?
• RQ5 To what extent can this conversion serve as a scalable model for expanding VLBI infrastructure across Africa?

Key findings

• The Nkutunse antenna successfully passed initial performance tests, demonstrating stable pointing and tracking capabilities suitable for VLBI operations.
• The custom ambient receiver achieved a system temperature below 100 K at X-band, meeting critical sensitivity thresholds for VLBI.
• The digital backend successfully recorded correlated data in line with international VLBI standards, enabling future network integration.
• The mechanical upgrades significantly improved the antenna's stability and pointing accuracy, reducing mechanical errors to acceptable levels.
• The station is now operationally ready for commissioning, pending final calibration and network synchronization procedures.
• The project establishes a replicable model for converting existing infrastructure into high-performance radio astronomy facilities across Africa.