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.

3. Build and use.

Lot's of ideas !