I have always wanted to create a Radio Telescope but assumed you would need a field which isn't going to happen.
However there have been projects where you can study the Hydrogen Line using a 'Horn' Antennae, Low Noise Amplifier, a Wide Band Amplifier and a Software Defined Radio.
I have recently suffered a minor stroke. There is no evident loss of cognition and it might be considered a TIA as the symptoms have now effectively gone. To exercise the part of the Brain affected I've been using a keyboard as this provides a specific target and will strengthen my muscles. This entry brings everything up to date before the minor stroke as to the progress of the project.
I am still constructing the Horn.
The 'corners' have now had the right angle 'spars' added which gives the overall dimension of the Horn.
It will be 750 mm wide and 600 mm high.
There still needs to be an element of being quiet so no more plates from the Cider cans have been prepared.
To help with construction I have bought and used a 'Digital Protractor'. The original purpose of this is to measure the internal angles of objects. I am using it to draw specific angles (22 and 17 degrees). With regard to 'aiming' the Horn I now have an instrument that gives a read out from horizontal in degrees.
Yes I could use my phone as it has a 'level' but it's not designed for this purpose and let's face it I'd rather in the field use a specific instrument that if it gets broken/dropped, isn't remove comms.
How do I know if the Horn is going to be any good, after all this isn't being made in a factory with extreme precision ! Well I started to look at this. As always Amazon provides and found a 'SWR Antenna Analyzer'. It has a range of 35 MHz to 2.7 GHz. The measurement of VSWR shows how much energy is returned back to a transmitter. By connecting this to the Horn I can see if there is anything that is reflected back at the frequency of interest, 1420 MHz.
The nearer the measurement to 1.0 the better. The first measurement was off the scale ! A huge number which did not bode well. I put my debug hat on. A further copper tube had been crimped to a N type connector as an investigation. A different cable was used so I made a measurement. It was down around 1.7. I then swapped the cables over and then remeasured. The measurement was around 1.6, a significant improvement ! Next question was am I just reading something about the cable or the Horn as a whole ?
Well I decided to put my hand in the Horn and wave it about a bit. This produced a fluctuation in the measurement thus showing that Horn as a 'system' was being measured.
In the web pages I've been following mention was made about a page that could calculate various aspects of 'Horns'. I've found this and it also gives options for different geometries. What is interesting is that it provides gain values for Circular Horns. This is of interest as I have a Nesquik tin that is circular. One of the other web pages I've seen uses a circular can and of all things cereal packets that have been silvered with tin foil ! It looks like I am NOT the first person to go the repurposing route ! Assuming that I can get the present Horn to work I might investigate this other route. One aspect that I have been wondering about is that this is a 'Dedicated' Radio Telescope. I think it would be interesting to see how to look into a more 'General' Purpose instrument. A further aspect that I have been thinking about is how to move and steer the Horn. Readers may have noticed that I have a further project which is a Processor aimed at being an MPPA. I would need to investigate it but it would be good to attempt the following 1. Create a Forth compiler
2. Work out an Alt Azimuth mount with appropriate feed back.
I have taken the expected dimensions from the web page that describes the project and confirmed the size of the Horn.
The numbers match those stated in the web sites drawing of the metal sheets. It was good though to walk through the basic geometry though. Once I had the angles calculated I started to cut up some Amazon packaging. I used a Protractor from a Geometry set I bought years ago as I thought it would be useful to have. These were best endeavours as the angles were 22 and 17 but these were decimals which a school protractor can resolve. Not to worry this is good enough. I have now obtained a digital protractor which is two steel rules with a joint and digital display showing the angle between the two steel rules. I will need this way further down the line.
Talking Protractors I have now also have a device which gives a digital read out of tilt angle, this will be useful to see where the Horn is pointed at.
I've updated the 'ariel'. Copper rod can't be 'soldered'. I tried to drill a hole in the copper rods I have but that didn't work out. Amazon can supply copper tubes, who knew !
A 2 mm tube is just needs a bit if a crimp to connect it to the solder point of the N Type connector.
I have plans for supporting the Horn, and it continues the theme of using cardboard and re-purposing.
Construction has started. I don't have any more prepared sheets as I need to be quiet for a couple of weeks, but can get some raw sheets cut out.
The Wave Guide has progressed quite a lot. Just one more small piece of aluminium to complete the wave guide. Then the next step once that is in I will start the Horn section. Here is the image admittedly this is old.
I've now consumed a load of shortbread and have an empty tin with which to put everything in. Note the 'plumbing'. This has been tightened up so it's stable free standing. To keep everything in place I have used some velco strip under the Wide Band Amplifier and the battery block that is on the left. There are three SMA connections, the RF input, a connection after the LNA and the final output after the Filter. It is also important to note the output from the LNA has a DC Block out to the middle connector and into the Wide Band Amplifier.
Due to bit of over aggressive deburring I had to create a dummy plate for the connections which you can see if you look close enough. However are the connectors and labelled.
Today's entry is related to seeing what I could see without any form of fancy pants Antenna, Horn etc. The first thing was to look at how good the Low Noise Amplifiers (LNA) are. H/T to James this is where I have first used the Vector Network Analyser. Put in very simplistic terms this tells you what your circuit or kit responds to a series of frequencies. For those with a greater knowledge it displays the transfer function in the frequency domain. There are other uses but let's just leave it at that for now. Not the Calibration was done but as it's a first I could possibly done better but this is indicative at the moment.
As mentioned in the previous post I decided to buy two LNAs so decide to look at their response. For those suddenly whimpering YES I did put a DC Block in ! I am not too sure if you can add labels to images but the first two images are the response curves. These are supposed to pass signals through at 1.42 GHz.
As you can see both have some ripple in the pass band. Chebycheff anyone ? After this I though what would a small telescopic antenna extended to 21 cm be like ? The reason being it's the simplest thing at hand so a good baseline. Effectively flung out of the window and see what I could see. Now back in Spectrum Analyser mode I scanned between 1.421 GHz and 1.427 GHz. Noise as you would expect so I turning on the averaging function. Noise being random should over a period time cancel itself out. However a constant level will stay. I tried an averaging of 900 and saw a tiny peak which appeared to stay. The other rather useful feature is the Water Fall Display, again this shows if something is disappearing and then reappearing, like noise.
The water fall seemed to show that this peak was steady. When averaged over 450 units it was still there. Now as you can see there are lot of smaller little peaks and I don't know what they are but it's all over the range.
Next I took the LNA out of the circuit entirely and had a look. No peak but also a lots smoother.
All in all I think a productive afternoon and gives me a good baseline to see how things progress.
I've been looking into this for a couple of weeks. I came into a little bit of money and was able to buy a Spectrum Analyser. Tuning into a local Radio FM Station was an unexpected thrill. Probably the most expensive FM Radio going but it proved a point that I could use it to analyse a signal and use the instrument.
I've got hold of some LNA boards and the components but also I've decided to get hold of the pre built units as described in these pages. The reason being as I am completely new to this arena and it's best to start to something I know works to help in the debugging of the inevitable issues that will appear. So let the adventure begin ! :)