COLD FRONT END

Stephen MuchovejCaltech

CONSIDERATIONS

• RF System Itself• Physical Considerations• Packaging• Mounting

RF System Requirements

• Noise temps of < 50K from 1-18GHz• 1% Amp Stability, 1 degree phase stability• Polar accuracy: 15 dB isolation• Ready in Fall – completely done by Summer 2013

RF System

• Note: amp symbols are reversed.

Horn Considerations - Spillover

Horn Considerations - Cooling

Possible Solution

Well-matched opticsLow spilloverFree Design

…only operates over factor of 6 in frequency. Means we have to split

the system

Telescope Focus Point2m in front of platform.We can put the two systems side-by-side, and cool all components in a single dewar.

Features• Better system temp ( <50K across whole band )• Perfect beam matching between two systems.• Lateral translation between

2 systems.• Need 15cm Vertical Translation between two feeds.• Needs to rotate to calibrate smaller dishes.

Mount Proposal

• Replace the mechanism up there with a full, self-contained system that

bolts onto the ring platform.

•Uses tracks for linear (and vertical -- focus) translations with actuators.• Uses a gear for rotation

• Install whole rx system at once• Adjust y once on installation

Mount Proposal

• Replace the mechanism up there with a full, self-contained system that bolts onto the ring platform.

• Allows for rotation and translation

Prime Focus Inventory•Rx and cryo lines.•Temp Controlled (TECA) box with:•Bias for amps•Temp Stable noise source•Temp monitoring•RF switch•Pre-amp module•RF-optical converter•Ethernet Switch•Ethernet controllable power supply•Small computer to control Noise Diode, Bias, and Alignment jig (rotation, x, and z)

TimelineOther people involved are Tomi Hovatta

(most machining) and Russ KeeneyMarch-Mid May: Component Selection and Costing, Rx

Design, and Support Jig DesignMay 15: Order RF components, Quotes on Machining

(that won’t happen here)May-July: Machining (Jig, horns, cryostat), control

subsystem developmentAugust-September: Rx construction, Mechanical testing

of Jig, Rx TestingOctober: Buffer Month.Nov-Dec: Installation/Commissioning

Still to define

1. Communications between small computer and control system

2. Amount of focus shift in pointing the telescope

3. Tolerances for Rx placement -- laterally and rotationally

4. Control of focus mechanism (distortion of dish)

5. Budget.