Carl Reade

Hi Coto unfortunately the dongle is now attached to a heatsink so can't really do a comparison. The chips were running too hot to touch before now they are just above room temp. I have seen them measured at 80deg. Heat is an enemy with radio so it will help with noise and stability. How much I cannot measure. I did notice most if not all interference spikes disappeared. The noise figure at the antenna/LNA sets the benchmark of the system and SNR is more important. The key to these setups are good antennas and the best LNA noise figure you can get hence they are cooled at the antenna in professional radio telescopes. Carl

Hi Robin thanks chuffed it's working. Yes to get the Yagi working I added a a reflector tin biscuit lid which helped big time and eliminated some ground noise. The feed is a biquad normally used for WiFi long range and works well with dishes. I used the following calculator. Use the second calculator the first is for a four-way. https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://buildyourownantenna.blogspot.com/2014/07/double-biquad-antenna-calculator.html&ved=2ahUKEwiNxNab8K3dAhWMLsAKHQVYB0cQFjABegQIBRAB&usg=AOvVaw1JCwSFCn-kzwmHTIRK8xWT There are various ways of making it. I used 1.5mm electrical solid core to make the diamonds. Would recommend using a copper reflector, I only had a piece of sheet steel and had to use a bit of copper circuit board to join the n connector to the element and screw together. I had to use elbow connectors at the back so the LNA was away from the dish arms in order to adjust, whatever works. Blow torch soldering is handy as well. A plastic tube hot glued is then the connection to the LNB holder long enough to adjust focus (which I need to do yet!) Mine is a bit messy but first effort. Carl

It works!! Set the dish up due South and roughly 70 deg elevation last night for a drift scan in the Cygnus area. was not sure if there would be anything as its a rough focal point and my engineering skills are rusty. I made an animation of 8 screenshots from 20:30 to 01:00 ish. Basically from start of pass to end with peak inbetween. This is live spectrum on screen with no processing. Its the highest resolution i can get on SharpSDR. The dish is a winner over Yagi which is no surprise. not so much signal strength but I think there is a lot more resolution. Setup is Dish with biquad feed 30db 0.5 LNA, 2 x inline sat amps 20db each, bias tee, Filter then SDR dongle. Hopefully the GIF works. Carl

The latest upgrade hopefully bit more gain. A 1.2m offset dish with a biquad feed. Have to say the feed was a tricky one to build adapting thing to fit was a nightmare but got there. The biquad was sized to work on 1.420Ghz via an online calculator. No doubt testing and tweeking to follow.

Hi Coto forget the docs it was just a bigger photo of the one posted. Forget Doppler at the moment. As the Hydrogen line is a very weak source to see in the noise (unless you have a very large dish) the best way to see if your scope is working is to point away from the miklyway and record a spectrum for 5 mins. This should be flat. Then point at the miklyway take another 5 mins recording. Place the two readings in a graph in Excel then divide the two and you get the difference between them. Which should be the hydrogen line. To get a good Doppler reading you then take a few hours of 5 mins recordings then place them all in a graph and you should see the hydrogen line hump move through the graph at an angle though time. The link I posted has examples in post processing under projects on the page. Carl

Hi the chart is a 2.4 MHz wide spectrum chunk centred on the hydrogen line around 1420.410. A live snap shot. It's in an Excel chart to define and enlarge. If that helps.

Hi Coto yes drift scan. I use a program called Sellarium to show when and where the Milky way is. I then use the alt/az to set the antenna using a compass and inclinometer. The beamwidth is 3db 15 degrees. Frequency 1.40 to 1.44Ghz. To produce the data I need to shut down Sharpsdr processes so it's running in the background then use another program to gather spectrum FFT data every 5 mins. This data can then be graphed in Excel. A quick way is to take a 5 mins file about and hour before the galaxy then one mid pass then devide the two in Excel on a graph and you will see the result. For processing here is a link to a site which is fantastic. With amature gear you are trying to listen to a conversation at a concert. This is one way of doing it. https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://parac.eu/projectmk3.htm&ved=2ahUKEwj6ot3d5KPdAhXDWsAKHdvQCS8QFjALegQIBRAB&usg=AOvVaw3JqQ9Z-YTu83lhKfmFUHoW

Thanks Robin indeed we do. It's quite a challenge but doable on a budget and a bit of patient learning. I will put a post on my setup and a really useful method of processing the data from a site I found ? Carl

An expnded view. Galaxy.docx

And there it is the hydrogen line through Cygnus ? It can be done.

One thing worth doing to the Sdr dongle is cooling. The chips and regulator on the board get extremely hot that you can barely touch. Six or seven large interference spikes have also gone leading to a smooth spectrum.

Hi Robin no noise from the sun when pointing. I think that is what I will look at first and start looking at eme setups. It's quite a tech challenge.

Amps and cables fine. Cannot tx on that band. The antenna feed is a short so also difficult to test. Think I will desolder the antenna feed to test continuity between it and the connector. I may build a horn type as well.

Hi well I have a filtered 30db 0.5nf lnb then two sat line amps both 20db followed by another filter and so far cannot claim success. I'm suspecting the antenna is not good enough however I have seen people use less and get results. The work continues. Carl

The tech has come on leaps and bounds fascinating stuff!

Great info and questions guys @Coto ipicked up this one on Amazon. It's well within Freq range.

Hi folks thanks for your interest and Corp will definitely have questions Im sure. The antenna came from the USA made by Directive systems some years ago. I had a go at this a long time ago but was never successful but technology has come a long way so thought I would have another go. Just waiting on the LNA from G8FEK which shouldd be here in the next day or two. Here's a pic of the antenna it's a long beast? Carl

Hi putting together a radio telescope, I have the following, A 45 element circular polarised Yagi for 1.4 GHz 20db A filtered LNA 30db nf 0.5db A satellite line amp 1.4Ghz filter A bias tee A SDR dongle Any help or tips appreciated. Carl