Your starter..

[rigdoctor99]

How many of you are radio hams or SWL's (short wave listeners)? If you are then you already have a radio telescope set up.

In th HF or short-wave part of the radio spectrum there is an allocation for radio astronomy, it is 25.55>25.67Mhz. This is used for radio Jove obserations, but it can be used for other things as well. I have used it to monitor the background noise from meteor showers, and the radiation from the Sun.

To get started you will need to cut 18.31Ft of wire, then cut that in half. connect 50 Ohm coax to the wire and string it up across the garden as high as you can, take the other end to you radio with whatever plug you need to fit your radio. Next install a program like 'Radio skypipe' on your computer, take an audio feed from your radio output to the mic or line input on your PC and start the program.

All you need to do now is tune the radio to a frequency within those I have given and listen for the rise in noise level.........

As I have said, I use this frequency but it is not the only one I can use.... I am able to go up to 42Ghz and down into a few Khz.......... OK lets get more of you using radio, then when condition are too bad to see the stars maybe you will hear them............... Thats it for now, and I am sure their will be many questions

[Ant]

This is going to sound blunt, but it is a genuine question - I am interested in the reply.

Why? what can you do with radio astronomy? I've seen the false colour images on TV and I'm guessing that I an't get those?

I've read about counting meteors by counting the spikes in noise, which would be quite interesting.

But what else is there to do?

Also why is the length of wire important? I used to use a CB radio, and the terms 1/2 wave and 1/4 wave are coming flooding back to me. But my memory is telling me that certain wavelenths require certain arial length, so wouldn't the 18.31ft of wire be specific to a certain frequency?

Also (sorry), would the two peices of 9.155ft be twisted together, or placed like a cross?, do they have to touch, or be soldered in the middle.

It's something that I may like to try during the next big meteor shower - cause lets face it - it's going to be cloudy

Ant

[Whippy]

Following on from part of Ant's question, I'm wondering if you have run any recordings through a spectrogram to see what the visual representation would look like?

Also, what kind of reciever would you recommend?

Tony..

[rigdoctor99]

OK Ant, the length of wire is a half wave for the frequency 25.55Mhz and you hang it out in a line with each end tied to a post of some kind. The only soldering to be done (if any) is the conection of the coax to the two peices of wire (one half to the brade and the other to the middle conductor of the coax).

As for what else can be done with radio astronomy, recording Pulsars, solar activity and the background radiation of the universe to name a few.... It is my hope to post more information on the ways it is possable to get into the radio side of astronomy without it costing too much, so that just about anybody will be able to give it a go......... I shall have to get the link for the radio skypipe software posted as well (its free) :mrgreen:

Hope this helps........ John

[rigdoctor99]

Following on from part of Ant's question, I'm wondering if you have run any recordings through a spectrogram to see what the visual representation would look like?

Also, what kind of reciever would you recommend?

Sorry Tony missed your post.... I used a lot SDR software on my PC for all sorts of jobs, but I must confess the thought of running the astronomy signals through then never crossed my mind.. Must give it a go!

As for receivers, Just about any short-wave receiver will do... As long as it has AM and SSB (just about all of them do now) it should be fine... The last time I checked E-Bay I saw some going for as little as £50.

Tony..

[Ant]

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A bit like that? obviously the two horizontal lines are the two peices of wire and the vertical is the coax. I'm wondering if I could get away with having them on my garage roof? Out the way then - no chance of getting hit/pulled etc

Does the length of the coax affect the frequency range of the wire. Coax is after all only copper wire (isn't it?).

I'd be interested in the visual representations as well.

Does the wire need to be anything special? could it, for example, be a 13ft length of twin and earth with the outer and earth removed. Could you leave the inner sheaf on?

I'd be interested in the software, if nothing else just to have a read up.

Cheers John

Ant

[Whippy]

Cheers John, I've been quietly hankering after one of those ICOM PC recievers, if I could link it into astronomy then it'll be a win-double for me .

Tony..

[narrowbandpaul]

I have done a course in Radio astronomy for my 4th year BSc...

basically the antennae generate a fluctuating voltage signal due to the EM radiation incident on it. This is a noise like signal. The signal is amplified and mixed with a local oscillator.

Even when you record the voltage signal, there is still so much noise from the amplifier and other electronics, that the signal is all but indistinguishable. What you get out of an observation is power per unit bandwidth...equivalent to a temperature. The aim is to convert this into surface brightness, by knowing the wavelength, bandwidth, aperture efficiency, gain, antennae temperature, sky temperature, solid angle of the object.

This would create scientifically useful information, but not pretty pictures. Optical imaging relies on good optics and accurate recording of data, whereas radio heavily leans on processing, Fourier transforms etc.

Unless all you want to do is here blips from meteors hitting the ionosphere, I would seriously consider a long think first. A degree in electronics and signal processing would be helpful.

This description is bad I know, but I dont fully understand radio astronomy.

But if you want to go for it....good luck. Let us know how it goes.

Cheers

Paul

[centroid]

Ant, the length of coxial cable will not have any effect on the resonant frequency of the antenna (dipole).

The only effect that the length of coax will make is in terms of 'loss'. However, at HF, its not as significant as at higher frequencies, and in your situation, you can ignore it.

The theoretical impedance at the centre of the antenna, will be in the order of 80 Ohms, but this will be affected by its height above ground. So 75 ohm coax will be fine for reception purposes. You won't need to worry your head about attaching unbalanced feeder to the balanced antenna either.

The thickness of the antenna wire, will only affect its broadbandedness (is that a word ? ), that is the thicker wire, the more broadband the antenna becomes. That is to say that it will still be resonant bit either side of the frequency it is cut for. Again, for this specific purpose, not an issue.

HTH

Dave

[narrowbandpaul]

hope it didnt sound overly negative, but the way we were told was so difficult that the gains possibly wont outweigh the difficulties

[Whippy]

Unless all you want to do is here blips from meteors hitting the ionosphere, I would seriously consider a long think first. A degree in electronics and signal processing would be helpful.

Not necessarily Paul, if you can get a simple reciever, some sound editing software and a spectrogram, I reckon it'll be interesting to see what you could come up with, both audio and visual. I spent a few years making music and most of my time was spent filtering out noise with a cheap editing program so you easily cut out the unecessary frequencies out and run it through the spectrogram to see the visual representation. Probably not at all scientific but it's another way of 'seeing' something up there .

Tony..

[narrowbandpaul]

sounds good tony.

but the way its done professionally at the like of the VLA (interferometry) make it out to be almost impossible.

It will be great to see what you get from EM radiation that is thought of as a wave!

good luck

paul

[rigdoctor99]

OK the picture should give a better idea of what I am trying to say..... I will dig out the link for the software as soon as I can.

Paul I think what you are talking about is the microwave systems used in VLBI, and for the sort of work done by those people I would say you are spot on about the noise floor. The whole system would be un-usable without the cooling system due to noise generated within the subsystems... But for the amature it is possable to do a lot of work in radio astronomy at a lower level.....

[narrowbandpaul]

fair enough...

good luck to those who try it....

like u say...radio astronomy works in all weathers

paul

[rigdoctor99]

http://www.radiosky.com/skypipeishere.html

The link for skypipe.......

[George]

With a fixed ariel are you not limited to what you can do?

e.g Pulsars, how would you know which star your listening too if you dont know which direction the noise is coming from? These are probably dumb questions but I know nothing about radio waves other than what i learned from my AM CB days (illegal then )

[dark knight]

Am I correct in assuming the aerial is basically just a horizontal Dipole. Also is it not also true that the angle the wire hangs will also make it sort of semi directional? A Yagi beam sounds like a good idea, as these are capable of covering a set of wavelengths ( usually used by radio hams) and are truely directional, meaning you can aim at a portion of the sky and at least you will have a rough idea as to where the received signals are coming from.. :scratch:

[dark knight]

Love topics like these, where there are more questions than answers

[rigdoctor99]

OK First, a Yagi would be better than a dipole it true. However, what I am trying to show at the moment is how easy it is to get started without costing large amounts of money. ( A Yagi for these freq. would set you back a couple of hundred pounds) It is also true that a dipole of this type has some directionality to it but it is a trade-off....

I wanted to get things started simply, and will be going into things like pulsars latter. ( For this you will need a beam) Also stepping up in frequency into the microwave end of the spectrum.......

Hope this helps...... And it is nice to see so many of you asking good questions. It can be the simple thing I forget to put in the post, simple because I take them for granted after 30 years.......

[dark knight]

And to think I sold my Ranger rci 2950 24mhz to 32mhz in order to take up of all things astronomy

[Dangerous-Dave]

Whenever anyone asks my opinion on amateur radio astronomy, I just trot out the old trusty equation:

Where R is the angular resolution of the telescope, Lambda is the wavelength of the electromagnetic radiation being observed, and D is the aperture of the telescope objective

So....

For visible light, say Lambda = 400–700nm

For radio emissions, say Lambda = 20cm (the typical search wavelength for pulsars)

To get the same resolving power as an optical telescope - if my maths is right - your radio telescope needs to be 300,000-700,000 times the aperture. :cheers: So, to replicate an 80ED you need a 40km array.

And that's before you even get into issues of background noise, as mentioned above.

On the other hand you can observe during the day and in full cloud cover.

I'm sure it'd be a fascinating hobby for techie people with an interest in radio, but you'd have to find satisfaction in false colour splodges!

[centroid]

I'm impressed Dave, how did you manage to get the Lamda symbol into the thread ?

Don't tell me that you've got a scientific keyboard

Dave

[Dangerous-Dave]

I'm impressed Dave, how did you manage to get the Lamda symbol into the thread ?

Don't tell me that you've got a scientific keyboard

Dave

Dave, I actually cut and pasted it from Wikipedia.

I'm not blagging though, I do have a BSc in Astronomy (albeit 16 years ago now... :oops: )

All Greek letters should be available on charmap! ?????? ?

[centroid]

Nice one Dave, and well done on the Astronomy BSc.

I did a first year part-time degree course in Astronomy, but then they shifted the course 40 miles away, and as I was only doing it for the fun of it, I 'dropped out'

Lamda has has been part of my life for 45+ years. I spent a career in RF/Electronics and EMC, and also taught radio frequency principles, part time.

Oops!!, sorry guys, we are taking this 'thread' a bit 'off track'

Dave

[Kaptain Klevtsov]

There's a bit about radio jove here:-

http://radiojove.gsfc.nasa.gov/

Basic start to listening to Jupiter using a rotating antenna (nailed down, so it turns once a day ) so you get a peak as Jupiter goes past the direction the antenna is aimed.

Kaptain Klevtsov