Telescopes

Page
6

Parts of a radio telescope

Receivers

Primary antenna

Secondary

reflector

Hat Creek Radio Observatory

Steering gear

Slide 58

Parts of a radio telescope

Antenna

Collects the radiation

Focuses the radiation on the receiver horn

Receiver

Horn

Amplifies the signal

Converts the radio-frequency signal to signals (current/voltage) we can record and analyze

Steering gear

Moves the telescope as it tracks the observed object

Slide 59

Antenna surface errors

The surface error (accuracy of antenna surface and shape) should be less than 1/20 wavelength to keep losses to less than 30%

This results in much more stringent requirements for

sub-millimeter telescopes than for radio telescopes.

Slide 60

Antenna surface errors

1/20l=0.05mm

Millimeter

1/20l=0.015mm

Sub-millimeter

Smoother

Smooth

Smoothest

NRAO 12 meter (1mm-3mm)

Kitt Peak

JCMT (0.3mm-2.0mm)

Mauna Kea

1/20l=0.15mm

Radio

VLBA (3mm-3m)

Mauna Kea

Slide 61

Antenna surface errors

This image was taken during the SMT reflector's holographic testing showing that the deviations of the reflector are nearing the targeted 0.015 microns (about the thickness of a human hair)

Slide 62

Parts of a radio telescope

Antenna

Collects the radiation

Focuses the radiation on the receiver horn

Receiver

Horn

Amplifies the signal

Converts the radio-frequency signal to signals (current/voltage) we can record and analyze

Steering gear

Moves the telescope as it tracks the observed object

Slide 63

Receivers

Horn

Purpose of the horn is to collect the radiation directed to it from the antenna.

Amplifier

Increases the amplitude of the signal

Mixer

Used to change the frequency to a more easily used frequency

Slide 64

Receivers

Store data

Radio

Amplifier

mixer (mix to

baseband freq)

Convert to

desired form to record/analyze

Store data

Millimeter

Convert to

desired form to record/analyze

Submillimeter

Store data

Convert to

desired form to record/analyze

Mixer

(mix to lower freq)

Horn

Slide 65

Reasons to use a mixer