USING THE BROADBAND DIGITAL RECEIVERS IN INTERFEROMETER OBSERVATIONS WITH THE URAN NETWORK

Abstract

Purpose: The goal of the work is improving the efficiency of interferometric studies of cosmic radio sources at decameter waves. Design/methodology/approach: The URAN interferometer network observations are made usually at frequencies of 20 and 25 MHz with the recorded bandwidth of 250 kHz. The URAN receivers provide an effective software filtering of interferences and reducing the redundancy of stored information during the recording. A software package developed for the URAN performs the further data synchronization and correlation, calculates the visibility functions, and determines the angular structure of studied objects. We propose to expand significantly the frequency range of observations and increase the number of frequency channels recorded simultaneously using the DSPZ digital receivers for signal recording. A number of narrower bands can then be chosen from the entire frequency range of 8 to 32 MHz of the recorded signals. The further filtering of narrow-band interference, reduction of bit capacity and further data processing are performed with the URAN software package. Findings: To implement this approach, we developed the software which singles out the narrow bands from a broadband signal and converts data storage formats and synchronization marks used in DSPZ to the form used in URAN receivers for information recording. We have observed the 3C380 quasar using the URAN-2 interferometer with the baseline of 153 km with simultaneous recording of signals with the DSPZ and URAN receivers. The data synchronization reliability at the interferometer sites, the efficiency of the interference removal automatic algorithm in a low-frequency part of the decameter range, the coincidence of the results obtained with the DSPZ and URAN were checked during observations. The paper also analyzed the possibility of expansion of the recorded data bandwidth to improve the sensitivity of observations. We considered the factors limiting the bandwidth at the decameter wavelengths and the conditions in which its expanding is possible are noted. Conclusions: The results obtained demonstrate the effectiveness of using the DSPZ receivers for the URAN interferometers. The flexibility of the proposed approach increase the number of observational frequencies to improve the accuracy of determining the angular structure models of the sources, expand the frequency range of the observations and increase the sensitivity of the studies.

Keywords

• interferometer
• decameter range
• digital receiver
• narrow- band interference