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The NAI C-NRAO School on Sin gle-Dish Radio Astronomy Techniques and Applica tions -- July 2005

Accuracy in Radio Astronomy
· Pulsar Periods: 1 part in 1012 · HI Redshifts: For z 0.1, about 1 part in 104 · Source Intensities and Polarization Parameters: Typicall y ±10%

The Measurement Process with Fully-Filled Apertures
Chris Salter (NAIC)

Basic Definitions
A: Intensit y/Surface Brightne ss: B: Brightne ss Te mperat ure:

D: Di stance De pendencie s C: Flux De nsity

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The Basic Radio Receiver
Celestial radio emissi on can be subdivided into two main spectral categorie s: 1. Broadba nd or C ontinuum E mi ssi on. Typical examples: (a ) planetary surface s, (b) HII regions, (c) the C osmic Microwave Background & (d) those Galactic and extragalactic source s t hat emit via the sync hrotron proce ss.

2. Line emi ssion due to low-e nergy tra nsitions within atoms and molecule s in space.

Terzi an & Lewis, (unpublished)

The Super-Heterodyne Receiver
Mixer : Why frequency change rather than amplify at RF all the way down the receiver chain? 1. Long cables are less lossy at lower frequencies. (Nowadays less important due to use of optical fibers. 2. Fear of positive feedback causing receiver oscillations. 3. If LO can be varied o ver a wide range, a standard, fixed frequency, IF chain can service a wide range of receiver front-ends. Detector:

Recorder

Signal-to-Noise Considerations
Syste m Noi se:

Cascaded Amplifiers:

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The System Temperature
Lossy Component s
There are extra noise-power contributions from such things a s; a) Emiss ion from the neutral atmosphere. b) Ground radiation in the far sidelobes. c) Celestia l no ise contribution s from; i) the background radiation of the M ilky Way. ii) the 2.7 K radiation of the Cosmic Microwa ve Background. iii) poss ib ly a contribution from the target source itself!

Where the sum of all contributions from outs ide the observin g system is called the ANTENN A TEMPERAT URE, T A.

The Radiometer Equation
How weak a source can we detect with a given r eceiver? For our total-power receiver, t he R AD IO METER EQU ATION gives the rms noise ripple agai nst which w e tr y to detect our target source, In units of tem perature ;

CONFUSION

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Let us consider a one-dimens iona l case;

Single-Dish Imaging and Sampling

? Convolution:
D = Te lescope Dia meter = Wavele ngth

How fa r apart should we place our sca ns (a nd how often should We sa mple along a scan) in order to lose no i nformation which our telescope i s capable of pa ssi ng?

TA De lta-fns

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