Making A Radio Telescope

[badgerchap]

Sorry, just edited those figures on account of being a Dilys....

[Gina]

Basically, anything that is built to receive at civilian or military frequencies is useless to us - we'll hear nothing over the blare of the channels already in use.

That is just what I thought. I think we will be looking at building a microwave receiver from scratch. I don't see this as an insurmountable problem.

However, there is a dedicated part of the radio spectrum reserved for Radio Astronomy. I just can't find it lol!

Yes, we need a clear band and one where there is something of interest. I don'y know but I would have thought some wavebands have more of interest than others. But I know diddly squat about this.

[Mr TamiyaCowboy]

Definitely, but they couldn't be signals of similar frquency of would interfere. I wa thinking more of converting a wireless dongle type thing into an antenna that would then be able to plug straight into a computer via USB - then it's all down to software from there....

yes a couple of the builds just show a usb dongle shoved into a dish , others used a household sieve. to boost the range.

the final build i noticed was a usb dongle mounted into a LNB case unit. and mounted to dish.

[Gina]

Really must do some more research before oopning my big mouth...

However, I do have some experience of radio waves plus some general theory. Some thoughts :-

1. The shorter the wavelength the smaller the dish for a certain angular resolution or you get a narrower (more accurate) beam from a certain size dish.
   
2. Dish gain is inversly proportional to wavelength and proportional to area.
   
3. Longer wavelengths are easier to build receivers for
   
4. Shorter wavelengths need more accuracy in the dimensions.
   

[badgerchap]

Those, to me, are some good reasons for starting at the sun - from the http://www.ukaranet.org.uk/basics/frequency_allocation.htm list, it seems the sun (Continuum) emits at almost all frequencies, so it's be good to start with a nice, low frequency (i.e. long lambda). This will make everything from reception to synchronisation easier. True, we wouldn't get much resolution out of this with the size dishes we're looking at, but then the Sun's a bit target, so it's be relatively easy for testing the principle?

[Mr TamiyaCowboy]

Those, to me, are some good reasons for starting at the sun - from the http://www.ukaranet...._allocation.htm list, it seems the sun (Continuum) emits at almost all frequencies, so it's be good to start with a nice, low frequency (i.e. long lambda). This will make everything from reception to synchronisation easier. True, we wouldn't get much resolution out of this with the size dishes we're looking at, but then the Sun's a bit target, so it's be relatively easy for testing the principle?

yes my thoughts to. something big, well documented and that everyone knows what it is.

the grail area is the 1400 - 1427 MHz range : 21cm hydrogen line so i had found others mention about radio telescopes, ( i have no clue myself)

something to do with ET/seti and likes

[Gina]

the grail area is the 1400 - 1427 MHz range : 21cm hydrogen line so i had found others mention about radio telescopes, ( i have no clue myself)

something to do with ET/seti and likes

Hmm... That's a long wavelength = BIG dish for narrow beam.

Re. the sun. Wouldn't that just be noise from the thermal process? Or would we be able to detect some sort of signal?

[badgerchap]

Hmm... That's a long wavelength = BIG dish for narrow beam.

Re. the sun. Wouldn't that just be noise from the thermal process? Or would we be able to detect some sort of signal?

From what I understand, you get varying frequencies from varying processes. With time, it's possible to identify distinct activity on the sun from radio signals only. I'm waiting for my lecturer to get back to me with the most interesting frquencies for Sol - this one is a solar physicist, so I'm hoping he knows lol

[badgerchap]

Just looking at that list again, I see the 1400-1427 MHz band is where galactic hydrogen would show up From what I was seeing on (I think) the UKRAA website, this is a fairly advance observation, so I think we could probably discount this for now, and focus on something that doesn't require so much experience?

[badgerchap]

Man, everything I read tells me something different. Now reading that solar flares emit right down in VLF at 23 kHz!

[Mr TamiyaCowboy]

a cliffside radio telescope detected sunspot activity way way back in the 1940's

so wiki has said while trawling for ideas and tips.

the H band is way beyond our realm

and the sun can be shadowed by background noise but can be detected when large sunspot activity is occuring (dont quote me on that )

[Enrico]

1400 MHz sits in between two major mobile bands (900 and 1800 MHz for 2G networks in UK).

Basically, anything up to at least 2.6GHz (possibly higher) is going to have noise from terrestrial based emitters.

[Auntystatic]

There is a section on the forum dedicated to radio astronomy, there are lots of resources and info in there, one thread I'm currently involved in is a hack of a tv dongle to receive signals from 64MHz - 1.7GHzon a computer or laptop these can be bought of ebay for around £10 - £20, also there is this http://www.lofar.org/ which featured on a recent sky at night. Here is a

.

[Mr TamiyaCowboy]

could the DVB-T act just like the LNB does ?

if so it brings the cost down alot.

but then could it be coupled to a Dish ie: 60cm dish and not use a fancy expensive aerial.

is there any difference ? ie way data is drawn together, could the dvb-t units be networked to act as one large unit

the same way we would network the dish's and lnb's

[jamespels]

Hadn't realised until reading through these posts above that we don't need an LNB as there is no need to down-shift the frequencies (we're not doing any fancy decoding or anything - just measure the amplitude of the signals we get) so a low noise high gain amplifier will be fine.

Reading around about atmospheric absorption at different frequencies, it looks like anything over 1GHz (microwaves, in other words) suffer some pretty heft attenuation and it all gets a bit tricky at higher frequencies as different molecules absorb RF at different frequencies (pretty obvious, I suppose, given that absorption spectra exist!). Looking at the history of the Lovell scope, the Mk1 was given a solid steel skin when the hydrogen line at 21cm was discovered in 1951. To me, this seems like a sensible starting point for us, too (TamiyaCowboy - is this what you mean by the H band and, if so, what would push it out of reach for us?)

Danielle, some very interesting stuff there - thanks for the links - trawling them at the moment!

J.

[jamespels]

could the DVB-T act just like the LNB does ?

if so it brings the cost down alot.

but then could it be coupled to a Dish ie: 60cm dish and not use a fancy expensive aerial.

is there any difference ? ie way data is drawn together, could the dvb-t units be networked to act as one large unit

the same way we would network the dish's and lnb's

Sorry, really not sure I'm following this. Had a quick read up and the only DVB-T I can find is terrestrial digital compression technique - am I missing something?

J.

[Gina]

DVB is Digital Video Broadcasting and I think the final T means Terrestrial. IE. broadcast from that gert big high aerial mast on yon distant hill. It's our standard digital TV broadcasting over an aerial. It uses the UHF TV waveband for digital terrestrial TV that replaced the wider analogue channels of analogue TV - hence the fuss of the change-over. The frequency is around 600MHz as I recall.

[Gina]

We would want just the receiver part - all the digital decoding is purely for digital TV and quite irrelevant and useless for our new application.

To use a dish one would have a small dipole aerial (called antenna in the US) at the focus with the signal fed down UHF TV cable to the receiver. A reflector could be used behind the dipole but we wouldn't want to narrow the aerial beam too much as we want to cover the dish.

[stonemonkeylives]

Interesting project,look forward to seeing it develop.

sent from Gherkin Muncher mk .III (commonly known as a Galaxy S2)

[Gina]

More thoughts on using UHF :-

1. A dish would have to be very big to out-do a multi-element Yagi array at this low frequency (long wavelength).
   
2. We would want to change frequency to avoid the actual TV broadcast band as has been said above.
   
3. It would make more sense to use an analogue TV tuner as it's analogue signals we are after.
   

[Auntystatic]

This is the DVB-T dongle that were on about, more info can be found in the link I posted earlier.

@Mr Tamiyacowboy

The LNB is a different beast to the DVB-T, it receives microwave signals, amplifies them then down converts them to a lower frequency so they can be sent down coax to a receiver box, the DVB-T is a self contained usb radio receiver, all it needs is an aerial, so lets say you want to receive the 1420MHz hydrogen line, it has a wavelength of 21cm, so a dipole would have 10.5cm-ish elements.

A better aerial would be a yagi (tv aerial shape) or a helix, both of these are highly directional and light at this frequency, it could be mounted directly on to your telescope like a guide/finder scope, it might need an LNA to boost these signals but these are easily made.

I'm using my DVB-T to receive the local radio amateur repeater station on 145.762.5MHz, also listening out for transmissions from the ISS when it passes over, one day I might even have my aerials in a position to talk to the astronauts.

[Mr TamiyaCowboy]

yes i think i got muddled up with "Radio" part and the receiver bits, you can tell i am learning.

i will stick to the hands on stuff.

heading out this week to grab some parts so i can start on a build.

is there anything consumer wise that will capture the signal, a converter or something.

could we get an arduino/blackfin etc etc to do this, having the usb already and pc connection could be handy ?

[Gina]

Here is a block diagram (rough drawing) of a typical analogue receiver as we would want for this project (as I see it).

[Gina]

Here is a block diagram (rough drawing) of a typical analogue receiver as we would want for this project (as I see it).

[garethmob]

that came through twice then gina im getting confused with the 2 threads im forgetting where i replied to lol

soooooooooo is the idea for the radio scope origionally a dish because of the similar shape to the professional radio scopes?

normal DVT usb things have a small problem in that they are limited to frequency, where the proper one thats been made and sold is open to most frequencys but it is only designed really for amsats

what we need really is a one chip does it all, with a simple "off the shelf" design for a arial, as DIY is ok but im not diy friendly and theres a few members who might balk at building it so really we need to find somthing thats available off the shelf to put together i thinks

id love to use my migila firewire DVT to do this as it works perfectly on my mac is this possiable?