Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/alfa/ealfa/meeting1/talks/lwray.pdf Дата изменения: Mon May 8 22:43:31 2006 Дата индексирования: Sun Dec 23 01:16:48 2007 Кодировка: Поисковые слова: molecular cloud

ALFA IF/LO System
Lisa Wray Edgar Castro
Electronics Division

ALFA IF/LO System

ALFA Galactic Consortium March 2003


ALFA Receiver System

Front End
§ 7 element feed array § corcal available § 40 dB gain § Bandpass filter module

Downconverter
§ Single frequency downconversion § RF: 1225-1525 MHz § IF: 150-450 MHz § Power monitor § Fiber optic converter

Buffer & Distribution
§ Divide signal to accommodate n backends simultaneously § Goal: High isolation between backends and monitor

ALFA IF/LO System

ALFA Galactic Consortium March 2003


Upstairs, after dewar and bandpass filter module · · · · · Single mixer conversion RF = 1225 to 1525 MHz, IF = 150-450 MHz LO either high-side: 1375+300 or low side: 1375-300 34 dB gain 58 dB dynamic range, limited by noise floor of fiber transmitter on low end (-45 dBm) and compression of fiber transmitter on high end (+13 dBm)

Downconverter

ALFA IF/LO System

ALFA Galactic Consortium March 2003


More

Upstairs, after dewar and bandpass filter module

Downconverter Info

§ Measured Teff = 750K
(contributes .075K to Tsys) § Anacom fiber optic transmitter: ­130dBm/Hz noise floor (-43 dBm for 500 MHz) § Fiber link is low-loss

§ Small light-weight surface mount design

§ Modular card cage

ALFA IF/LO System

ALFA Galactic Consortium March 2003


Buffer + Distribution
Downstairs
From fiber optic receiver To monitor & backends

· · · ·

Receive signals from fiber optic cable, put on coax Provide enough buffering to isolate backends Provide distribution network for backends Monitoring: one path dedicated to monitoring

ALFA IF/LO System

ALFA Galactic Consortium March 2003


More on Buffer + Distribution
· Divide signal to accommodate n backends ... how many?
­ WAPP is the dedicated backend ­ Others: Pulsar, Extragalactic, Galactic, SETI

· Monitor
­ 14 IFs brought out to control room ­ Slow Sample (fixed tau) and record for debugging/ problem solving

ALFA IF/LO System

ALFA Galactic Consortium March 2003


Acknowledgements
· Bill Sisk · Ganesh · Dudes in receiver section

ALFA IF/LO System

ALFA Galactic Consortium March 2003