Making A Radio Telescope

[Mr TamiyaCowboy]

cooling is best simple for the time being, going complicated could cause more problems.

a simple tec hooked to a certain voltage should be fine enough. no good reaching for -20

better to hit just above -0c or just below.

mounting wise, a little silver arctic, and a couple zip ties will do. if we can get the electronics close together,

we can use a simple cold finger to cool a couple of the major heat producers.

LNA, these are built into the LNB units. low noise amp + downconverter = LNB ( what i gather from wiki)

will have a google session see if anything can be made breadboard style that could help us.

also the breadboard style could leave us open for extra electronics to be added. and requires near to no soldering.

i could do with a newbies guide to radio and the likes. i have no clue what i am doing ( tuning, wavebands etc etc )

[Auntystatic]

Some resources for you....

http://www.ukaranet.org.uk/

http://www.radiosky.com/index.html check out the beginners section

http://www.mtmscient...otelescope.html

http://www.backyarda..._telescope.html

http://www.jb.man.ac...lsar/index.html

http://hardhack.org..../export/html/18 takes a while to load

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

[jamespels]

Thanks Danielle,

one of those links (one of th first two) references noise reduction though a fairly simple mechanism. This got me thinking...

If we have a large dish (say 3m) and a uch smaller one (60cm Sky antenna or similar) pointed exactly the same direction, we could use the smaller dish to record "noise", perform a little pre-amplification to bring the gain at our chosen frequency up to that of the main dish and then use it to cancel out main signal noise prior to the main LNA. This would need some fairly clever signal processing but should be achievable, particularly if we then track a point in the sky to give an average over time (essentially like stacking LX frames in imaging).

OK, I know ttis is fairly complex and there are a couple of challenges to overcome but nothing that should be insurmountable for somebody with good digital signal processing skills. If it works, it will mean we ned to relay a lot less of electronic filters.

Any thoughts? Any volunteers for investigating this?

[Gina]

Sounds interesting. But I see a flaw in this. Wouldn't the smaller dish also pick up the signal if pointing in the same direction as the larger one? Also, the noise would only be the received noise - the thermal noise in the receiver system would be different for the two devices and would NOT cancel.

[Gina]

Thanks for the links Danielle I'll read thropugh them when I have time

[Mr TamiyaCowboy]

Thanks Danielle,

one of those links (one of th first two) references noise reduction though a fairly simple mechanism. This got me thinking...

If we have a large dish (say 3m) and a uch smaller one (60cm Sky antenna or similar) pointed exactly the same direction, we could use the smaller dish to record "noise", perform a little pre-amplification to bring the gain at our chosen frequency up to that of the main dish and then use it to cancel out main signal noise prior to the main LNA. This would need some fairly clever signal processing but should be achievable, particularly if we then track a point in the sky to give an average over time (essentially like stacking LX frames in imaging).

OK, I know ttis is fairly complex and there are a couple of challenges to overcome but nothing that should be insurmountable for somebody with good digital signal processing skills. If it works, it will mean we ned to relay a lot less of electronic filters.

Any thoughts? Any volunteers for investigating this?

the DSP.

could the data produced be recorded in a WAV format ?

if it can, we could then use say something like a software defined radio, you are able to imput either raw I/Q or a wav file, to look at the spectrum produced ?

thats the software side dealt with fairly simple. and playback could be via the pc's soundcard.

LNA i found one on maplins @ £5.99gbp

Based on the NE5532 chip with independently adjustable output levels (gain typically 100)

Operating voltage: 3V to 25V ( maybe use the LNB powersource to run amp to)

Input impedance: 1kohm

( NE5532 PDF) http://www.maplin.co.uk/media/pdfs/N47FL.pdf

is the above any good by viewing the pdf layout ? maybe we could add better components.

[jamespels]

Sounds interesting. But I see a flaw in this. Wouldn't the smaller dish also pick up the signal if pointing in the same direction as the larger one? Also, the noise would only be the received noise - the thermal noise in the receiver system would be different for the two devices and would NOT cancel.

This is either the clever bit or a resounding fail... I am counting on the source signal being significantly lower than the noise recorded by the smaller dish. I was thinking of amplifying the smaller dish's signal to match the level of the unamplified main signal so, with the signal : noise ratio, we SHOULD keep the signal from the main dish intact.

Thermal differences in gthe dishes will remain, though, unless anybody has any good ideas here?

EDIT: Regading the thermal differences in the dishes, from what I have read, they will be substantially less than at least the man-made interference. Would the long exposure approach reduce this by averaging out some of the thermal noise?

[jamespels]

the DSP.

could the data produced be recorded in a WAV format ?

if it can, we could then use say something like a software defined radio, you are able to imput either raw I/Q or a wav file, to look at the spectrum produced ?

thats the software side dealt with fairly simple. and playback could be via the pc's soundcard.

Thanks Mr Cowboy - is this something you could look into in a bit more detail? Sounds interesting...

[Mr TamiyaCowboy]

well me and auntystatic run SDR software capturing radio waves ( shortband radio/fm, usb,lsb,cw bands)

i am just learning myself, can say getting device running was a right royal pain.

the way it works is fairly simple.

a receiver chipset sends I/Q samples direct to the software. the PC becomes the workhorse well its audio card does, this converts the signal into audio via headset.

so a antenna plus to the receiver with built in LNA, sends the raw data to the sound card, the soundcard and pc decode signal to audio.

no sending of signal just a pure receiver. the grunt end is the PC cpu's and its onboard /thirdparty soundcard.

via wav, a wav file is loaded into the software defined radio, its then sent to the spectrum readout and converted to signal. i am looking for a test wav to have a play with the software see what it all does.

i have also noticed defined noise, possible from the way the chip set requires a 1.5v source, the adc wants 3.3v and the usb pumps in 5v, so its got to be dropped down somewhere and this causes a noise. if its showing on my device it is possible it could show as ghosting on the lnb type setup.

i have picked up on 153mhz a signal that looks to be a weather station repeater, am yet to pick up any Shortwave or longwave. aerial is the most important thing. get a $2 radio and a $200 antenna.

i think the way to maybe go is the satellite dish route, but use jove radio receiver style electronics. its proven to work and we can gleen info from other projects.

basic receiver is the way to go i think. maybe convert a maplins component kit.

pointing the dish could be simple, a small Laser mounted centre of the dish, turn on align and of they go. all that would be needed is a starmap/ star app, daytime a simple signal meter could be used

maybe even go to the extreme of a single target wavelength say 21mhz-40mhz , two fairly easy areas not so prone to getting flooded by fm and the other rubbish.

a simple jumper design could switch between the two bands.

ultra wideband and the likes i think just complicate things. what wavelength etc etc. if its a fixed wavelength all thats needed is to fine tune the signal received.

that reminds me i need a new solder iron and my feet pounding the maplins shopfloor

[Mr TamiyaCowboy]

very informative link about using dishes as antenna's

gives meaning and explains how they work

http://www.radio-electronics.com/info/antennas/parabolic/parabolic_reflector.php

[jamespels]

OK, some progress to report on construction...

slight change from plywood frame to solid styrofoam with a fibreglass backing. I am now planning to use a DIY CNC machine as this can be really simple: divide the dish into 30 degree segments, hot wire cut to close to the right curve then use a 2 axis DIY CNC setup to mill out to the exact curve. Switching from x, y, z coordinates to theta, y, z means we can pivot one end of the CNC arm then mill out in arcs to give a very precise surface (0.5mm accuracy from a friend who has done something similar). I have found a product called StyroSpray 1000 (from here: http://www.industrialpolymers.com/) that effectively self-levels the open cells in the styrofoam and gives a smooth finish; this will then be metal-coated using electroless nickel plating. EDIT (or metallic paints: will try both and compare - paint will be a lot cheaper).

Initial setup of this stuff isn't going to be simple but it should be very repeatable to make pretty much any size of dish within reason.

On a separate note, I have also nearly completed a spreadsheet mapping dish size, estimated efficiencies, atmospheric absorption etc. by frequency to give performance projections - looks like the best option for us is definitely going to be around 1 - 3 GHz in the short term - ideal for the 21cm H line. I should be able to finish it off this weekend and will post here when I have.

J.

[Gina]

Very good James - looking forward to reading more of your efforts and results

[Mr TamiyaCowboy]

would it be possible to receive X-band: 8400-8450 MHz ?

to what i gather voyager 1 transmits in this region, and is well a good distance away.

that would be some holy grail data to receive.

i am getting more distance with my radio experiments, am now able to pick up local tower/radar/approach coms.

hope to have a discone antenna soon, and want to build a helix feed sat dish ( direction type)

[StuW]

Having read through most of the pages I can't help thinking that using sat dishes is going to both over complicate things and the size of the dish will limit the input signal strength. If I was going to target the 20 - 30MHZ band for Jupiter I would probably use the aforementioned DVB dongle coupled to (depending on room available) either a full or half sized G5RV (I could receive the US on 20m band with it simply wrapped around the inside of my attic) . I'm no expert, I only got to the Intermediate Amateur licence, but I'll offer any help where I can.

[yesyes]

The question is how directional we want/need this. To receive radio broadcasts (Voyager 1/2, ISS, ...) it probably doesn't have to be extremely directional. For a radio image of a specific object, however, we would probably need the receiving angle as narrow as possible.

[Mr TamiyaCowboy]

would need some upconversion to get 20-30mhz. the usb receiver is only good for 64mhz - 1700ghz ( 2100ghz possible somehow)

[Gina]

20-30MHz is at the top of the HF band and you'd need a large aerial array to get directionality at that frequency. A totally different field from microwaves or even UHF.

[StuW]

A sloping V would give directionality at HF wavelengths, pointed toward the ecliptic it would work quite well. Obviously this isn't suitable for ppl with limited space.

[Auntystatic]

LNA i found one on maplins @ £5.99gbp

Based on the NE5532 chip with independently adjustable output levels (gain typically 100)

Operating voltage: 3V to 25V ( maybe use the LNB powersource to run amp to)

Input impedance: 1kohm

( NE5532 PDF) http://www.maplin.co.../pdfs/N47FL.pdf

is the above any good by viewing the pdf layout ? maybe we could add better components.

Sorry but that is for a stereo pre amp, an LNA is a RF amp that goes on the "front end" of the system, basically attatched to the aerial. Here you go try these for a better understanding......

http://www.downeastmicrowave.com/PDF/1420ulna.PDF

http://home.comcast.net/~prutchi/index_files/astronomy.htm I like this site after only a quick glance, it seems to have everything I need.

http://www.radioastronomysupplies.com/radio_astronomy_supplies.php?cat=CAT&id=2&name=LNA%27s%20&%20FILTERS

My Jova rig

The DVB-T will only go as low as 64MHz so you won't be able to listen to shortwave (3-30MHz), forget using the G5RV just make a dipole with 2 lengths of wire @ 3.54m long each side.

If you have a license you can talk to the ISS with a 5 watt walkie-talkie, but as its traveling at around 17,500mph you only get a maximum of 10 minutes each pass.

My plan is to make an aerial or 2, mount them to the scope so I can image what I'm pointing at and watch the graph as the mount slews. An LNA will be attached to the aerials and the DVB-T directly to the LNA, to keep signal paths to a minimum.

[StuW]

Hey Danielle,

I managed to get a short QSO with MIR while being supervised by a G0 many years back, and was what actually got me interested in radio. I eventually saved enough pennies for one of these..

Unfortunately I had to give it up due to financial circumstances.

My personal interest at the moment is VLF, which is a LOT easier and cheaper now thanks to SL6LKM's SAQrx software.

[Stargazing_Cliff]

Mite get one them satelite starker kits sometime in july after 10th

and point it one stable position or mite get movable portable dish thing would need that special stuff making for it so can connect to me pc and you guys get data from it when my system uploads you guys can make me special box sometime.

will let you satelite dudes know once i have me dish

seen couple them nice looking satelite finders also look interesting. pick up some channels also aswell as astronomy stuff with dish

[jamespels]

Small update - I have the samples from the Styrospray people and it looks very good. The brush finish is very smooth - appears to be around 0.1mm roughness - and reasonably tough, though it is a little softer than I would like. It also peels off quite easily if forces so it will need to be edged well but, all told, it looks like it will give a very good surface.

Now to try it out on two small dishes and see whether metal paint or electroless plating is the way to go.

J.

[athornett]

Hi folks,

Thought you might be interested that there are quite a number of folks doing amateur radio astronomy in the UK. Probably the most active group is the BAA Radio Astronomy group - http://www.britastro.org/radio/

My own group's work in the area, with many simple and relatively cheap projects, can be found at www.radio-astronomy.me.uk

Andy

[athornett]

Hi folks,

Thought you might be interested that there are quite a number of folks doing amateur radio astronomy in the UK. Probably the most active group is the BAA Radio Astronomy group - http://www.britastro.org/radio/

My own group's work in the area, with many simple and relatively cheap projects, can be found at www.radio-astronomy.me.uk

Andy

[jamespels]

Been meaning to post this for a while - I have found myself with a little time on my hands so here goes.

The initial calculation spreadsheet is complete; for a given set of basic parameters it gives approximate predicted performance and the geometry of the dish in terms of surface x & y coordinates. I have colour coded the anticipated gain and half-power beam width (HPBW); it is pretty obvious that for anythin we can make on an amateur basis, there is going to be a sweet-spot around 2-4GHz.

The spreadsheet also gives the exact shape of the templates needed to form the parabola for the given dish (see the method I am going to use further up this thread) and I will be ordering to machined aluminium templates to these shapes later this week.

For practical construction reasons (I have found some cheap styrofoam at .6m wide), I am going to make the dish as seven hexagons 1.2m across. This gives a total area of 7.56sqm and an effective diameter of 3.1m, in case you were wondering where the odd diameter came from.

Before I go any further, can you please check over the spreadsheet to make sure I haven't made any dreadful howlers? Also, everything I can find suggests a focal ration in the region of 0.5 to 0.6 is about right for the focal ratio but I cannot find any good reason to choose one f over another, with the only obvious impact being in wave-guide design. Any thoughts on this? My current thinking is to get the dish working with just the inner hexagon but with the final collector supports so I can add the other panels as I get round to making them; to start with, the dish will have an effective diameter of just over 1.2m so the f ratio will be around 1.4 - is this going to cause any obvious issues?

Cheers,

James.

telescope.xlsx