«Amateur Radio Astronomy How to start. Jean Marie Polard [F5VLB - 2016] The book you need to understand and operate an amateur radio astronomy ...»
Amateur Radio Astronomy
How to start.
Jean Marie Polard
[F5VLB - 2016]
The book you need to understand and operate an amateur radio astronomy station,
It is free, may be freely distributed, but nothing can be changed and the source must be cited.
Thank you to Miguel A. Vallejo EA4EOZ for the technical reading an to Peter & Heather for the English
F5VLB-EA4EOZ– 2016 Amateur Radio Astronomy… How to start.
At the beginning
The beginnings in brief
Why this syllabus?
Sources of Radio Emissions
Its size, its shape
The half power beam width @ -3dB (HPBW)
What is inside a LNB/LNC ?
Which one ?
The next step : the detection
The satfinder (my first love)
The power injector
Another solution : The RF probe
Digitalization of a signal
Jim Sky's software
The Arduino module
Forecasting and analysis software
Sidereal Clock for Your Desktop
Why Dimension 4 ?
Sensitivity of the System
Minimum Detectable Signal Program by Dave Halley
Processing the data
Verification of the opening angle
Calculating the brightness temperature (Tb)
Verification of the LNB position and alignment of the antenna
Projects of radio telescopes
The other planets
The Milky Way and the line H²
The powerful radio-sources
The HEP (high energy pulses)
A realization among others
The sat finder
The power supply
The analogic digital converter
Tracing and recording software
Some links to continue
In the beginning...
The beginnings in brief Karl Jansky discovered in 1933 a radio signal with a period of 23 hours 56 minutes, a sidereal day, the characteristic period of the fixed stars move. This is the first extraterrestrial radio signal received on Earth. In 1937, Grote Reber, having failed to get hired in the team of Jansky, built a radio telescope at his own expense to ex plore space in the radio field, as an amateur.
After World War II, research began on a larger scale with recycled military equipment (radars). In France, in 1947 Yves Rocard with two German original antennas of 7.5 m diameter creates an observation service run by Jean-François Denisse. In 1952 he obtained the means to build a bigger radio astronomy observatory station in Nancay (France – dpt of Cher) with 32 radio telescopes aligned, inaugurated in 1956.
March 25, 1951, Harold Ewen and Edward Purcell detected the 21-cm line of neutral hydrogen in the Milky Way with a horn antenna.
In 1963, Arno Allan Penzias and Robert Woodrow Wilson discovered the residual radiation of the Big Bang un der George Gamow trying to eliminate background noise in their transmission equipment.
In 1965 the cosmic microwave background is discovered. Georges Lemaitre (a Belgian) had predicted in his the ory of the early explosion in his article (in French) addressed to Sir Eddington, defines it as the "glow disap peared from the formation of worlds", connecting the theory of Big Bang; what Fred Hoyle, a supporter of the "stationary" theory, had caricatured by appointing this term big bang which thus became the symbol of the theory of the expanding universe. The discipline of astronomy takes an unparalleled boom in the history of as tronomy.
In 1967, Jocelyn Bell Burnell detected the first pulsar, but it was his supervisor, Antony Hewish, who received the 1974 Nobel Prize in Physics for his contributions to astronomy - triggering a controversy.
Source : Article Radioastronomy on Wikipedia This young science was built by many radio ham's like Grote Reber, John Kraus, Joe Taylor...
Why this syllabus?
Since I became interested in radio-astronomy a lot of progress has been made. At first, the difficulty of access to information was a handicap. Now, with the internet and Wikipedia, with modules available at low cost, any one, with a little skill can make a radio telescope and make beautiful experiences. Certainly there are lots of books, articles, information sources. This syllabus is trying to consolidate all that we could store and to share some of my experience. Feel free to go elsewhere to complete the job and make your station, a good station.
Also share your knowledge, your trials, your successes and your failures. Thus it progresses.
Good reading ….
My first radio astronomy station in... 1971. I was listening to the sun and Jupiter with a broadcast radio. No computer, no graphic recorder, no spectrum analyser, no money... just the ears and eyes.
During the 2000s and using the sound card as an interface between the radio and PC. Listening meteor echoes.
I spent hours in front of the 'Spectrogram' spectrum analyzer and analyze the results with the help of EA4EOZ Miguel. With the end of analogue TV, listening meteors has become more difficult to discover the Graves radar explained below. With Miguel, we deigned our first radiometer based on the Satfinder. Probably one of the first developments in radio astronomy using satfinder ever.
In 2014, I bought my first house and installed a wooden garage with the new shack.
The satellite dish of 155 cm will be doubled by another of 2.4m from RF-Hamdesign.
The 2,4m dish antenna (picture from RF Hamdesign ) Info here
For each of these sources, one has several options. I start now with the equipment.
The equipment The antenna The key element in RA is of course the antenna. As in optics, it will be used to capture radiations. So its size, shape and position will be crucial to achieve good observations.
Its size, its shape An antenna can be made with a tight copper wire between two poles, one or more yagi antennas, a dish (offset or prime focus), a horn … What will determine the type of antenna you will use is the frequency of the radio waves or radiations on which you will work.
If you work between 0 and 10MHz a loop antenna is effective, between 14 and 100 MHz a dipole antenna will suffice, between 100 and let's say 1000MHz a yagi, and above a dish or a horn.
A simple antenna to listen to Jupiter can be made using two copper wires tendered between two poles or two fixed points and that's all. Wires of 1.5² or 2,5² and covered with plastic is perfect. Attached to the fixing points by nylon wire 1m long, for example. Do not tie directly to the insulators hanging points. Between 18 and 24MHz, you can detect signals from Jupiter. See below.
If you are working above 100 MHz, to listen to the sun, pulsars, meteors, a yagi antenna is recommended.
This kind of antenna can be found in all the tv stores, ham radio stores, or can be built by yourself, for the most skillful. It must chosen based on the frequency you will be working. One can assemble several yagis one beside the other, one on the other, remote from each other (interferometer).
Above 1000MHz, the dish is preferred. So either you opt for a small offset type of dish (the same as used in satellite TV) purchased commercially or recovered at home or dumped (there are beautiful treasures in waste, with their LNB and sometimes motorization ). Either you take a prime focus for larger diameters.
But one thing is evident the greater the diameter the more signal you can capture. That said, with a 60cm off set dish there is already way to do great work, especially on the sun.
If you have an offset parabola, you may need to find the focal point where to install the LNB. Jean Louis Rault F6AGR has posted a worksheet that can help you. See this link for the calculations excel sheet of F6AGR This sheet is in French, but with this example you should find your way.
Cette feuille de calcul permet, à partir de quelques mesures effectuées sur une parabole de récupération de caractéristiques inconnues, de déterminer la position de la source, son orientation, et d'estimer le gain de l'ensemble.
Ces résultats sont théoriques, et les valeurs données sont à affiner avec des mesures menées en terrain dégagé à l'aide, par exemple, d'une balise émettrice fixe.
1. Mesurer la hauteur, la largeur et la profondeur maximale de la parabole et renseigner toutes les cases en bleu-vert
Vous pouvez adresser vos remarques, questions et critiques par courriel à f6agr@w anadoo.fr
Physique et Théorie du Radar de J. DARRICAU Articles de F4BAY dans bulletins Hyper Simulations NEC de G6LVB sur antennes hélice Reference Data for Radio Engineers (ITT) A similar sheet exists for prime focus dish http://www.setileague.org/software/parabola.xls but not only, a long list of useful xls sheets also !
O F : is the focal length The gain We use this formula
k = performance of the illumination system (source) averaged 0.55 (for small dishes, 0,65 for large ones) D : diameter parabolic reflector : wavelength used D and are expressed in the same unit example: a parabolic dish of 155cm will have a gain of 33,3 dBi @ 4GHz (λ = 7.5 cm) check with the excel sheet of the previous page The half power beam width @ -3dB (HPBW) We use this formula θ = 57,3 λ/d 57,3 comes from 180/pi θ = angle of aperture in degrees (the beam) λ = wavelength in cm D = diameter in cm example: a parabolic dish of 155cm will have a HPBW of 2,77°@ 4GHz (λ = 7.5 cm) one can see a difference between our calculation and the one on the excel sheet … This is because 57,3 λ/d is just a handy approximation. The excel sheet gives an exact value.
The radiating element of the source must be at the center of the dish where all the energy is concentrated. To illuminate entirely the reflector, it is necessary that the diameter thereof corresponds to the radiation lobe of the antenna source. The focal length ratio / diameter (f / D) is a key parameter of the parabolic reflector. It is chosen between 0.4 and 0.8. A ratio f / D too low gives a very compact antenna and requires a source with a large opening angle. In contrast a ratio f / d higher gives a more compact antenna using a more directional source.
Higher F/D ratios produce bulky antennas. Not so compact as lower F/D values.
In the figure, the source S has an opening angle @ 10dB (red line) which corresponds to the angle 2Φ under which the parabolic reflector P is seen from the home. The lines in magenta represents the opening angle at
-3dB. The part of the lobe colored in cyan-blue misses the reflector.
Given two parabolas 60 and 100 cm in diameter. Given their ratio f / D, it will take for one a source whose opening angle is 50 degrees while the other will require 80 degrees. Well-trimmed circular cones may agree.
(1) source http://f5zv.pagesperso-orange.fr/RADIO/RM/RM09/RM09i03B.html The motorization This is a very delicate point... because accuracy is required. Personally I prefer a mount in meridian position and make transits. To motorize a large parabolic dish requires application and technology. But rather see what is involved.
For an offset type antenna take a look at the link below (1) which explains the positioning of an antenna facing the Clarke belt where are positioned the television satellites. To adjust the height, it will add a jack.
(1) here is a pdf of the commercial company manufacturing the equipment on the picture above. Another interesting site here For a prime focus, we will use either one azimuth / elevation couple of motors (expensive) or two actuators (one for azimuth and one for elevation).
Wiring of the module to the Raspberry.
Its position To start, I suggest you position the antenna facing south. Indeed, a star rises as it passes the meridian. The right ascension of a star is constant, the value that is maximum at the transit time is the elevation (height above the horizon)
To calculate the elevation of the antenna you must know the latitude of your location, and apply the formula:
elevation = 90 – latitude of your location + declination of the radio source example : if the moon rises to -15 ° when it passes the meridian (hour angle 00h00) and you are at 48 °
N latitude, it gives:
90°-48° + (-15°) = 27 ° elevation of the antenna relative to the horizon the free software "Stellarium" automatically gives you the azimuth and height : in the example 180 ° azimuth (south) and 26 ° 12'59,9 ''. But it is good to know how to calculate it.
Transit time is determined by the right ascension of the object and the local sidereal time. When the value of the local sidereal time is equal to the right ascension of the object it 'transits'.
The duration will therefore depend on HPBW (see above) and the declination of the 'object' using the formula:
t = 4 / cos (declination) * HPBW t is time in minutes and HPBW is the opening angle at half power of the antenna.
Conversely, if one measures the transit time of a star, we will be able to determine the HPBW....
The antenna must be firmly fixed on a support itself in a concrete, or a stable support. We can not imagine a telescope that trills, it is the same for an antenna. The motorization is a luxury, but not insignificant once one has mastered the system. It will allow a source to be tracked and enable different measurements than of a sin gle transit.