Radio astromony

[smenkhare]

I've never seen anyone sell antenna's etc marketed for astronomy, what would be need to DIY it? (something more than listening to meteors on your am radio)

can anyone help?

[bojan]

You need antenna (suitable for frequency band you want to observe), AM receiver for that frequency band (with noise figure as low as possible) and recording device (computer with ADC for example).
That's about it...
What you will be able to with this setup depends on antenna and it's directivity, more narrow the beam is, better the resolution you will have.
What precisely do you want to do?

[Terry B]

Take a look at http://www.radio-astronomy.org/
Lots of info.:D
An Australian site and project is at http://fringes.org/

[smenkhare]

not really sure.
other than the typical search for life, maybe looking at black holes, quasers, a backup for when the skies are too cloudy for optical astronomy.

[bojan]

Oh oh..
for this scope of work you will need a BIG antenna... and very sophisticated data processing software.
It is relatively easy to detect some strong sources (like Cygnus A for example, 3m dish and the receiver in 3GHz band with normal sensitivity (NF =10dB) is enough.. but this is about it.
I wanted to do this kind work for my master's (but never completed it).
But other, more interesting tasks require specialised equipment, with detectors that are suitable for the purpose.
For example, to detect pulsars, receiver must have very fast response (very little integration, which is normally used for detecting transits through antenna lobe, for example), that means it has to be very low noise (perhaps it must have cooled or even maser-type LNA).
This equipment is very expensive (part of the reason is, antennas must be physically big, just like telescopes).

[bojan]

The easiest target to observe is Sun... It is possible to monitor burst of radio noise from active areas in 1-3m bands.
Also, some people are monitoring the signal strength from distant AM radio-stations, which varies due to atmospherics (perturbations of the ionosphere) influenced by solar wind.
For this kind of work the equipment is relatively simple.

[Gama]

I recently discovered a black hole that was eluding me for years. Found it in my wifes purse !.
Money keeps going in and i never see it again..Plus my wife claims to never have seen it either ?.
Mysteries of the world.

Theo.

[smenkhare]

ah so radio astronomy is considerable more expensive than optical.
guess i'll just save for that OTA then.

[bojan]

Well, not really... optical is also very expensive..
But radio does not give "visual" results, it is more remote in terms of engagement of our senses..
With telescope you can really see things, but with radiotelescope you can very rarely only hear (a noise, only slightly louder that thermal noise of the receiver), and what you will see are only graphs and numbers..
It is different.

[tempestwizz]

My understanding of the topic:

Visual astronomy will produce a much more resolved understanding of the etheric mostly due to the wavelength/aperture of the 'acquiring system'. Visual astronomy captures wavelengths in the visual range, ie some 600 nanometres down to 400-ish nanometres. Radio utilises much longer wavelengths. I believe Ha has a radiation at about 1620 MegaHertz - which has a corresponding wavelength of about 18.5 cm.

For say a 100mm visual device, it is some 200,000 wavelengths across at 500 nM. For a radio antenna to equate at 1620 MHz, it would need to be 37 kM in diameter! Clearly, this is impractical. The result with smaller aperture radio antennas results in a less defined result. The beam widths of typical antennas are in the order of 30 degrees. Hence hot, (or warm) areas of the sky can be detected, but not with much resolution.

Also radio astronomy is effectively like looking through a 1 pixel camera. We can get a 'brightness' value for the pixel, but unless we methodically scan an area of the sky to produce a brightness map it wont relate to any visual observations.

However, unlike visual observations, the atmospheric turbulence will have little affect on the instantaneous 'brightness' of the radio signal.Hence an AM demodulated signal would be a trrue reflection of galactic (not atmospheric) noise.

VBR

[bojan]

Not quite true..

Athmospheric turbulence (especially in ionosphere) has the same if not bigger effect (and that strongly depends on wavelength), resulting in "twinkling" of the radio sources..
Also, interferometric methods (using two or more wider spaced antennas) can result in drastically increase resolution..
But in terms of "1 pixel camera" you are basically right...
And, some objects will be vert "bright" in radio bands, but invisible in visual.. that depends on mechanism that generates radiation.
Also some wavelengths pass through our atmosphere un-affected, some are blocked with water vapuou or other gasses, some are affected by Van Allen bands...
As I said, radio0astronomy is different, and complements visual (and other short-wave bands), resulting in more complete picture of the universe we are trying to put together.

[Suzy_A]

You can also pick up a fair bit of radio emissions coming from Jupiter and Io due to the electric current that flows beween them. Also as someone else mentioned, lots of stuff from the sun - places like Learmonth and Culgoora do the solar stuff - http://www.ips.gov.au/Solar/3/4

When I was at RAAF Learmonth (which is the other side of the road from the observatory) they would ask us not to use 245 MHz as it would fry their gear...

Anyway, the large - 3 or 5 m satellite dishes - make quite good radio telescopes for the higher frequencies (over a gig or two). For the lower frequencies, stacked Yagi arrays or similar work well. Have a look at the ARRL handbook and antenea handbook. As for the receiving gear, you need to make up your own horn etc and you need a good low noise pre-amp. I bought one from ... somewhere in the US. I'll post the website later.

For the lower frequencies (less than about 1.3 GHz) you can use amateur radio gear or something like the WinRadio http://www.winradio.com.au/ which goes upto 3.5 GHz.

For the higher frequencies, either pays lots of money or make your own...

Most of this stuff you can also use for satellite communications as well and often a lot simpler stuff will do for satellite - I've spoken to the crew on the space shuttle a few times, once using a hand-held radio. Obviously if you want to transmit as well as just receive, you also need the right licence.

[smenkhare]

Chatting to the shuttle? legally?

well i've got a radio telephone operators license so all set in that regard.

[Suzy_A]

I haven't done so recently, but yes, it is possible. I also spoke to a few Russians on MIR when that was up and running. They sometimes are on about 145.450 MHz which is in the amateur radio band, so all you need is an amateur radio licence, plus some gear of course!

Several years ago I helped a friend who is a school teacher and we set up my gear at the school and had 5 students and the school principle talk to the crew on the space shuttle. Each student got to ask one quick question - the length of the pass is only about 10 minutes. That was with a tracking yaggi antenna. With just a whip antenna, you only get about 5 minutes or so.

[robgreaves]

Yes, U3MIR is in my logbook from years ago, I had a quick chat with them on 2m FM when they were passing over the UK in the early hours of the morning.

I've heard shuttle transmissions on 2m, but haven't had a QSO with them yet.

Regards,
Rob G0MOH - in need of a VK3 ticket now :)

[renormalised]

How about setting up a radio interferometer.....instead of one large dish have a series of smaller dishes. Although, the setup for that would cost a pretty penny too....plus its complexity would be fairly substantial.

[AussieSky]

You mean something like this ?

http://www.aussiesky.net/SRTInfo/srt.html

Greg

[smenkhare]

Now THAT looks nice

AussieSky: Nice to see another hobbit. :P