Initially developed in 2020 under the RadioNet project (EC GA 730562), the BRAND (BRoad bAND) receiver has been successfully tested and partially commissioned at the Effelsberg 100-meter radio telescope, marking a significant advancement in radio astronomy. Designed by Gino Tuccari (INAF) with contributions from MPIfR, OSO, ASTRON, Yebes Observatory, and Ventspils International Radio Astronomy Centre, the receiver supports VLBI and single-dish observations across an impressive continuous frequency range of 1.5 to 15.5 GHz.
The BRAND receiver features cutting-edge components, including balanced amplifiers and 56 GSps high-speed digital sampling boards. Its direct sampling architecture eliminates the need for analog IF transmissions, simplifying operations and enhancing reliability.
Expanding Observational Horizons
The broad bandwidth of the BRAND receiver offers unprecedented flexibility, particularly for studies of redshifted spectral lines and rapid frequency agility. These features make it a game-changer for the European VLBI Network (EVN), where the ability to observe a wide range of frequencies without changing receivers during a session could transform observational efficiency.
Recent tests and initial integration of the BRAND system have proven its potential. For the first time, its analog frontend was installed at the Effelsberg telescope and subjected to on-sky testing. The single-dish spectra of the W3 molecular cloud was successfully recorded and a repeated NME session in C-band with Medicina, Yebes and Onsala achieved VLBI fringes across all baselines, with the best performance being Efelsberg-Medicina. A notable achievement was the detection of 62 radio recombination lines in W3, underscoring the receiver’s sensitivity and frequency range.
Overcoming Challenges
The integration process, while ultimately successful, was not without its hurdles. Due to the digital board lacking a shield to stop RFI from further propagating in the primary focus, the experimental setup differed from the intended setup of the BRAND receiver. This meant to use a link (RF-over-Fibre) to transfer the RF signal from the primary focus down to the Faraday room. The wide bandwidth had to be divided first into 4 GHz bands and downconverted and then recorded with the spetrum analyzer in Effelsberg with a bandwidth of 2.5 GHz. Therefore, the full observed spectrum in our first test on W3, shown above, goes from 1.5 GHz to 12 GHz.
The testing phase revealed several technical challenges, including setting up the optimal noise levels, and the intermodulation of the RFI at around 1.8 GHz and 2.1 GHz in the RF-over-Fibre link. Furthermore, mechanical adjustments of the Dewar – the cryogenic unit that cools the receiver – required further refinement to optimize focus across the full frequency band. Despite these setbacks, the on-sky tests confirmed the receiver’s basic functionality, with system temperatures recorded around 90 K and no major issues detected in initial observations.
Future Prospects
Looking ahead, further testing and refinements are planned to address the known issues. Priorities include hot-cold testing with liquid nitrogen for improved temperature measurements, focus adjustments for high-frequency observations, and shielding the digital frontend from RFI. Once these challenges are resolved, the team plans to conduct technical reassurance observations, full spectrum of 1.5-15.5 GHz observation and pulsar observations to fully characterize the system’s performance, including sensitivity and aperture efficiency.
Beyond Effelsberg, the BRAND receiver could replace multiple single-purpose receivers at other EVN stations, offering significant cost and operational efficiencies.
Image 1: © A. Roy/MPIfR; BRAND receiver box installed in the primary focus of Effelsbger radio telescope
Image 2: © P. Rahimi/MPIfR; The 1.5-12 GHz spectrum of the W3main cloud with the detected RRLs marked inred lines. Yellow lines show an example in eachobserved band. The full spectrum is formed by putting together 2.5 GHz spectral pieces received by XFFTS in Effelsberg
RadioNet has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730562