The New (2003) L-Wide Receiver

The new L-wide receiver was installed on the telescope in February 2003, where it replaces the old L-wide receiver that had been in place since the upgrade. The electronics department page for the receiver is here

The new receiver is a dual channel, cryogenic, native linear polarization receiver. The frequency range of this receiver is the same as the old: 1.15 - 1.73 GHz, but the horn, dewar design, OMT, amplifiers, and polarization module have all changed. Measured Trx range from 7 to 11 K as a function of frequency and its Tsys (on the telescope) similarly ranges from 25 to 40 K. The system temperatures (on the sky) from the engineering tests show that the current Tsys is about 24 K at 1660 MHz, and about 30 K at 1300 MHz.

The feed is a new ring-loaded design by German Cortes of NAIC, Ithaca to replace the Ying-Kildal feed from the old L_Band wide. We expect the spillover contribution to be reduced compared to previous horn (-16 dB edge taper compared to -12 dB)

The OMT (ortho-mode transducer) is a quad-ridge linear polarization design by NRAO Green Bank, who fabricated and tested the unit. This is the same type of OMT as the old L band wide, but has far fewer resonances (4 compared with 17 in the previous OMT, at 1255, 1437, 1598 & 1720) and is a more compact design. The dewar design follows the GBT L Band receiver design.

The cryogenic amplifiers are from NRAO Charlottesville. They are 3-stage PHEMT LNAs with noise temperatures of 2 - 4 K when cooled to 16K. These replace older Berkshire amplifiers with similar performance.

The polarization box is another significant change. It was re-designed by R. Ganesan to allow for more reliable operation and lower noise contribution to Tsys. It is the module that changes the linear response to circular. It also includes a new band defining filter and a new post amplif ier. The band defining filter helps attenuate the RFI at 1000 - 1100 MHz and at 1850 - 2000 MHz.

The filter bank module follows, and allows the user to select a combination of high pass filters and narrow bandpass filters. It has been slightly modified by adding some isolators to smooth out bandpass ripples.
The block diagram.

The IF system offers power level monitoring and adjustment, and a selection of IF and bandwidth combinations for the upconverted signal. Scans of the response of most of the filters are here.

Details of the horn can be obtained through the pdf documents available here

Photos of the horn (in the development phase) can be found here

>From now on, the above receiver parameters should be used when submitting proposals for the L_wide receiver.

last modified 6 March 2003
Murray Lewis, with much help from Lisa Wray