Home Built telescope first images

[pasaphil]

Hi,

I have been working on a home built radio telescope for a while and currently still working on the mount and tracking so no ground breaking stuff yet. I have however been imaging the Clarke belt to optimize the tracking so thought I would upload a couple of images that I have been able to scan. These are using a 70cm dish and a standard LNB and an Alt Azimuth mount with home made controller and the zoomed image is of the UK sky TV satellite.

Hope some of you find this interesting.

Phil

 

 

[Carl Reade]

Hi interesting, how are the images made from the data?

Carl

[pasaphil]

Hi,

The LNB output is fed to a log detector and then a 12bit ADC.  I then take the high 8 bits and use them as an offset into a colour map which is a 256 pixel wide bitmap. The colormaps are used in various software and can be downloaded as small bitmaps. The one I used was called inferno. Then I read the pixel at the offset address and added it to a bitmap at the x,y position to get the nice coloured image. The original 12bit data I stored as a DICOM image to retain the resolution.

 

Phil

[JamesF]

So is the image representing the strength of a signal at a specific wavelength?

James

[pasaphil]

Hi,

It shows the signal strength at the 10Ghz band used by Satellite TV transmissions and is a raster scan of the sky at 0.05deg per pixel.

 

Phil

[JamesF]

Ahhh, that makes sense then.  I understand now.

So presumably you can tune it to work at different frequencies because looking at TV satellites is going to get boring fairly quickly What do you have planned for it?  Maps of the CMB?

James

[pasaphil]

Using the geostationary satellites is good for alignment but as you say not particularly useful beyond that (nothing worth watching is ever broadcast). The idea really was to build a steerable mount with controller that I could attach either a dish or yagi and sync up a few of these to make an interferometer which is why I went for a high pointing accuracy. The telescope part is quite open once the mount works well. I still have to add the sidereal tracking code for solar and lunar observations but this should not be too hard and I have already done a few test solar runs and it works well. Dish size is going to be the limiting factor for many things but the mount should handle a 1.8M dish so it's not quite a lovell but should generate some interesting data. Also it should be good for tracking the non geostationary satellites as it can slew nice and fast.

 

Phil

[Stub Mandrel]

1 hour ago, pasaphil said:

Hi,

It shows the signal strength at the 10Ghz band used by Satellite TV transmissions and is a raster scan of the sky at 0.05deg per pixel.

 

Phil

Check out those airy discs!

[pasaphil]

A 70cm dish has quite a wide beam so it will be interesting to see how this changes when i get two of these sync'd up 30 meters apart (I have 3 of them)

 

Phil

[JamesF]

Are there interesting radio frequency observations to be made of the Sun and Moon then?  (Apologies for all the questions.  This is a topic of which I am woefully ignorant.)

James

[pasaphil]

There are lots of solar observatories out there and radio emissions are in many ways far more interesting than the visual disk. Probably not the best time to image the sun coming into a grand solar minimum but you should be able to image the sunspots and flares etc and track and log emissions. Moon is a lot weaker signal but should still be fine with a larger dish fitted. Most of the things NASA is looking at will not register at all on a small dish so you have to look at what is possible for the amateur  and the solar system is workable.

[robin_astro]

Detecting the Moon is easy with a small dish and a satellite finder at this wavelength eg my simple setup here

http://www.threehillsobservatory.co.uk/astro/radio_astronomy/radio_astronomy_1.htm

but the resolution is only ~2.5 deg.  You would need a very big dish or dishes on a long baseline to begin to resolve any solar features.   (1 arcmin resolution would need ~100m aperture at 10GHz)

Robin

[robin_astro]

Take a look at this recent thread as an example of what can be done with a small dish. (Milky Way Hydrogen line observations)

https://stargazerslounge.com/topic/319651-anyone-doing-hydrogen-line-observing/?page=2&tab=comments#comment-3508554

Robin

 

[robin_astro]

The main area of solar radio work done by amateurs is not what you might think as traditional radio astronomy using big dishes but monitoring Sudden Ionospheric Disturbances (SIDs) using long wave radio receivers,

https://www.britastro.org/radio/vlf.html

Robin

[pasaphil]

9 hours ago, robin_astro said:

Take a look at this recent thread as an example of what can be done with a small dish. (Milky Way Hydrogen line observations)

https://stargazerslounge.com/topic/319651-anyone-doing-hydrogen-line-observing/?page=2&tab=comments#comment-3508554

Robin

 

Hi,

All interesting things for me to try. I did start with drift scans of the sun and just wanted to get more data faster and could never be sure exactly where the dish was pointing so I wanted it much more precise so I could try some interferometry.  The pointing accuracy is 0.05deg but the dish beam width is closer to 2-3 degrees so I I'm currently tinkering with locking two PLL LNB's together and syncing to the GPS 1PPS time signal and having two dishes 50m apart (best I can manage here) and possibly one in a different location but I need to sync them to 250ps so not impossible but challenging as the raw 1PPS is +/- 10ns

Phil

[robin_astro]

Yes phase locking LNBs sounds tough. Much easier at 21cm where you can combine before downconverting.  Ive sometimes wondered if it might be possible to get interference fringes on brighter galactic sources at 21cm with a couple of say 1.8 dishes

Robin

[pasaphil]

I am going to try my hand at aperture synthesis but with the telescopes cabled together so it's just a timing delay issue rather than the bigger problem of synchronisation issue on different sites to start. There are open source correlators out there and a 3 node scope is pretty low tech for serious radio astronomers (hi tech for me at the moment). Got the double oven OCXO + DDS running and sync'd so will give it a go in the new year. Might even make a video and stick it on youtube for people as nerdy as me ?

[robin_astro]

1 hour ago, pasaphil said:

I am going to try my hand at aperture synthesis but with the telescopes cabled together so it's just a timing delay issue rather than the bigger problem of synchronisation issue on different sites to start. There are open source correlators out there and a 3 node scope is pretty low tech for serious radio astronomers (hi tech for me at the moment). Got the double oven OCXO + DDS running and sync'd so will give it a go in the new year. Might even make a video and stick it on youtube for people as nerdy as me ?

What are you using for LNB ?  Are they standard domestic TV ones? if so how do you get into them to sync the local oscillators ?

[Stub Mandrel]

3 hours ago, pasaphil said:

I am going to try my hand at aperture synthesis but with the telescopes cabled together so it's just a timing delay issue rather than the bigger problem of synchronisation issue on different sites to start. There are open source correlators out there and a 3 node scope is pretty low tech for serious radio astronomers (hi tech for me at the moment). Got the double oven OCXO + DDS running and sync'd so will give it a go in the new year. Might even make a video and stick it on youtube for people as nerdy as me ?

Do it the old-fashioned way, use exactly the same length of co-ax for each dish and don't coil up any excess lead (or wind it anti-indudtively (double into a hairpin then make a very open coil so the co-ax gores round both clockwise and anti-clockwise).

[robin_astro]

7 minutes ago, Stub Mandrel said:

Do it the old-fashioned way, use exactly the same length of co-ax for each dish and don't coil up any excess lead (or wind it anti-indudtively (double into a hairpin then make a very open coil so the co-ax gores round both clockwise and anti-clockwise).

It doesn't work if you are downconverting at the dish LNB unfortunately (which you would normally be doing at 10GHz) unless the individual local oscillators are locked in phase. If you dont,  you lose coherence. It is feasible to do this at 21cm though where you can use matched low noise amplifiers at the dish to offset loss in the feeders and combine the coax feeds before the main receiver

Robin

[pasaphil]

3 hours ago, Stub Mandrel said:

Do it the old-fashioned way, use exactly the same length of co-ax for each dish and don't coil up any excess lead (or wind it anti-indudtively (double into a hairpin then make a very open coil so the co-ax gores round both clockwise and anti-clockwise).

That was what I had in mind but i was going to just coil it so I learned something today as I'm more used to keeping everything small and typically 10cm for RF cables.  Local oscillators are going to be phase locked as the PLL type LNB's use a standard Xtal so I will run a separate 27Mhz feed to each LNB from a common source, remove the Xtal's and tune the lengths in the same way but at 27Mhz it's not too hard.

Phil

[pasaphil]

4 hours ago, robin_astro said:

What are you using for LNB ?  Are they standard domestic TV ones? if so how do you get into them to sync the local oscillators ?

I'm using a cheap domestic Optima Octagon but these modern units use a cheap Xtal and PLL to generate the Local Oscillator so can be locked by pulling the Xtal and injecting the Xtal frequency into multiple units.

Phil

[niallk]

Very cool! I've been considering trying out something like this