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: http://www.naic.edu/alfa/galfa/docs/galspect/downconverter/gain_control.html
Дата изменения: Mon Oct 4 01:40:37 2004 Дата индексирования: Sun Dec 23 06:27:41 2007 Кодировка: Поисковые слова: п п п п п п п |
Each of the 16 downconverter boards has an independent gain control. These gains are adjusted by an 16-channel digital to analog converter board (16 8-bit DAC's). The 16-channel DAC board is sent serial data using two control lines on the RS232 port of the CompactPCI CPU board.
The gain controls are 8 bits each, where 0 is maximum gain, 255 is minimum gain.
Gain in dB is roughly linear with control voltage (ie., gain is logarithmic with control voltage). There is about ~45 dB gain change over full scale.
See Figure 12 on the AD8348 data sheet (available from Analog Devices) for a plot of gain vs. control voltage.
DAC Number to GALFA Channel Mapping:
| DAC 0 | Beam 0 | POL-A | Real & Imag |
| DAC 1 | Beam 0 | POL-B | Real & Imag |
| DAC 2 | Beam 1 | POL-A | Real & Imag |
| DAC 3 | Beam 1 | POL-B | Real & Imag |
| . | |||
| . | |||
| . | |||
| DAC 12 | Beam 6 | POL-A | Real & Imag |
| DAC 13 | Beam 6 | POL-B | Real & Imag |