Cassegrain antenna on the rooftop of IUT (Bangladesh) academic building. It was brought for communicating with the satellites of SingTel. In fact it was used as a VSat. IUT has taken BTTB internet connection. So VSat is of no use now. We have taken this chance and implementing this dish antenna to build our Radio Telescope.
side view. there are two antennas. we will only use the satellite antenna. Don’t have any intention to build interferometer.
Dish mount alongside the transceiver
Transceiver: (We are not sure about it’s use. Maybe only receiver portion can be used.)
COMTECH EF DATA
Model no. – CSAT/5060S-010
Tx RF freq. – 6.425-6.725 GHz
Rx RF freq. – 3.4-4.2 GHz
Detail view of Transceiver.
LNA (Low-noise amplifier)
RSC Model no. – 3346
Input frequency – 3.4-4.2
LNA
Secondary reflector of the Cassegrian antenna.
Transceiver with cables.
Details of our project
IUT Computer Centre was connected to internet by a VSAT. But after taking optical fibre connection from BTCL, VSAT has become idle. IUT wasn’t using this for almost a year. Now we have come to fill that gap. We have taken all the accessories and instruments of VSAT to build a Radio Telescope. We have got the following instruments from the CIT department of IUT:
– Cassegrian dish antenna
– LNA (3.4-4.2 GHz, C-band)
– Transceiver
– Satellite modem
– Router
– Necessary cables
But the main problem is with the driving mechanism of rotating the antenna. The antenna is huge, so it is not possible to rotate it manually. We need a automatic rotating system to track the stars and moon. We still don’t know about the availability of rotating motors and control system for dish antenna in Bangladesh. So, it’s still not solved.
Transceiver
We can use the receiver part. Specifications of the receiver part are:
Received frequency: 3.4-4.2 GHz
Gain: 45 +/- 1 dB
IF frequency: 70 +/- 18 MHz
Gain without LNA: 45 +/- .75 dB
Gain flatness: +/- 0.75 dB Full RF Band
Image Rejection: 60 dB In-Band
Gain stability without LNA at 0 dBm o/p level: +/- .25 dB
Outpur power: +13 dB
Noise figure: 11 dB
Intermodulation: -50 dBc for two tones at 0 dBm each, 1 MHz apart
IF o/p VSWR – 1.25:1
RF i/p VSWR – 1.25:1
IF o/p impedence – 50 ohm
RF i/p impedence – 50 ohm
Functional Block Diagram of the Downconverter in Transceiver.
The RF input to the Downconverter is in the 3400 to 4200 MHz frequency range at a typical level of -45 dBm. The input signal is mixed down to the 1110 MHz IF in the first conversion mixer. High side LO injection is used for this mixing process. The Downconverter RFLO synthesizer in
the 4510 to 5310 MHz frequency range provides it in 1.000 or 2.500 MHz steps. Both step sizes are automatically selectable.
IF filtering is provided by the 1110 MHz BPF. It is just wide enough to pass the 36 MHz bandwidth of the desired signal while maintaining more than adequate amplitude and group delay flatness. At the same time, it is narrow enough to provide the necessary rejection to the image, the RFLO, and other spurious signals. The second mixer operates at a fixed input frequency of 1110 MHz. It operates with high side LO injection at 1180 MHz provided by the Downconverter IFLO and converts the IF signal down to the 70 ±18 MHz output frequency.
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