Return to WebMaster's Cygnus-A remark

G4FAS 173.2 MHz Radio Telescope
( Phase-switched interferometer )

Inspired by a series of articles by John Rainey Smith in the Journal of the British Astronomical Association
1970 August Vol.80 No.5; 1970 October Vol.80 No.6; 1974 August Vol.84 No.5

Illustrative view of Antennae and electronics

Illustrative view
Two ten element Yagi aerials looking skywards on an
east / west base line and spaced about 22 metres apart.
If observed from a point on the terrestial equator the virtual lobes would seem to be
4.5 degrees apart, equivalent to a diurnal period of 18 minutes per lobe.
My observations at 53 deg N are somewhat  different i.e. showing a timebase distortion
of about 1.66x and therefore an apparent diurnal period of 30 minutes per lobe.

Rustrak paper chart showing passage of Cygnus A

Penned as Cygnus-A whispered through the virtual lobes presented
by the pair of 10 element Yagis spaced 22metres apart.

Electronic modules


A vintage Hameg spectrum analyser served as an ideal receiver
due to its appropriate bandwidth of about 5 MHz.
Oscilloscope to monitor loading of the phase sensitive detector.
Antennae phasing switch ( sq.wave driven ) / Gulton/Rustrak 2" chart-recorder /
L.F. amp;  phase sensitive detector 
(sq.wave driven);  D.C. amp & 1000Hz square wave switch
The lowest unit is an experimental 30 MHz intermediate frequency amplifier.
Not shown are E<->W (20dB/CF439) aerial pre-amplifiers / and other test-instruments /
a stabilised 12 Volt P.S.U. for all solid state modules, including the aerial pre-amplifiers
which receive their D.C. power via the aerial cables.

Noise bridge @ Noise head

G4COM noise comparator inc noise head

Link to a diagram which shows how two separated (and coupled aerials) provide a virtual grating on the Sky.

External link to Journal "Nature" Vol.161, No.4087, pp.312-313 (28 Feb 1948)  Astronomers J.G.Bolton & G.J.Stanley
Go to charts of other objects
Credit is due to (the late) "Electrovalue" component emporium of Burnage for their
excellent component catalogue; store-keeping and counter service.
Sadly as with many other similar establishments they are long gone.
( How are today's science teachers coping ? )

Most of the hardware including antennae and copies of the relevant BAA journals are offered (for approx. material cost)
to anyone who can convince me they will go to good home.
But first consider the following quotation from an old  B.A.A. "Nature, Aims and Methods" handbook : --
   " - - - anyone capable of building a television set without detailed instructions should (be able to) manage a radio telescope. "