BEST - 3lo

BEST-3lo (LOw frequency) was the third phase of the BEST project. Eighteen log periodic antennas were installed in a part of the East-West arm of the Northern Cross Antenna. BEST-3lo works in a frequency range between 120-240 MHz. Considering 36 receiver just installed in the BEST-1 and BEST-2 we have totally 54 receivers (36 in the N-S and 18 in the E-W) and an overall collecting area of 2.400 square meters.

Picture below shows the block diagram of the BEST-3lo system.

The log periodic antennas are able to receive a wide band from 120MHz up to 240MHz. Since this bandwidth is used for a common broadcasting signals, lots of interferences are received from the antennas. Unfortunately the level of this undesired signals could saturate the receivers. An analogue filter bank were installed on the front end to reject the portion of the band affected from the strongest interferences. A control board inside the box permits to set the desired filter. Then the signal is sent to the processing room through an analogue optical link. There it is amplified, filtered again and it is directly sampled at the original frequency (direct conversion). Picture below shows the box installed on the E-W focal line.

Each box serves two log periodic antennas, so contains two front-end, two lasers, one controller board and one power supply board.

The BEST-3lo and BEST-2 share the same back end (same ADC and same BEE2 processing board). In order to select the right input signal from BEST-2 or from BEST-3lo, an analogue switch is provided.

The first fringe (figure below) was obtained correlating the signals coming from the BEST-3lo receivers in the bandwidth 138-142 MHz. The radiosource observed was the Sun.