saac

14 hours ago, Mr Spock said:

James T Kirk and crew contaminated every planet they stepped on. So much for the prime directive 

That was probably a story line - crew return with alien bacteria on skin which gets transmogrified in the teleport and so ensue cataclysmic deep space warp factor 5 danger will robinson series of unfortunate events      

Jim 

To see those live at the eyepiece must be a real joy. One day I will own an NV system . Thanks for sharing that GavStar  

Jim 

At the end of the day some time in the near future humans will land on Mars. From that point onward concerns over contamination become redundant .  Anyway, Im sure there are a variety of ways of telling the origins of molecules ( isotope mass numbers etc). We know that certain isotopes occur in what ratios on Earth and I'm sure on Mars by now.   Like I said though, once we set foot on the planet with a view of holding down a permanent presence then it all becomes irrelevant. 

Jim 

A moment in history  

Jim 

I was always taught that our laws of physics are only our interpretation of what we think is going on based on what we know and what we observe.  At any given moment our laws are then at best an expression of our interpretation and may not ultimately reflect reality .  Not that we will ever know what that ultimate reality is   

Jim 

7 hours ago, planetman83 said:

Guys, what do you think? I managed to make it fit in my car. I have to make some improvements to the wheels so it can go up in the car easier.

Lovely design, well done. I think I may steal some ideas from your design for the wheelbarrow arrangement - at the moment I have to lift this all and it's getting a bit heavy now  

Jim 

6 hours ago, Corncrake said:

 

Guess this one may be the prototype !?

 

Yep that was the intention. I invested in the components that I can reuse (filter, cable connectors and SDR dongle) the rest I can remake fairly easily once perfected.   I think I have a solution to the mismatch - find smaller can lol    Guess who is doing a recce of B&Q  - I don't care what the contents are I just want the can  

Jim

6 hours ago, Carl Reade said:

Hi here a link to a really useful site which helped me enormously. http://www.parac.eu/

Take a look in the project section  especially project 3 and 9 in the list.

Regards Carl

Carl, many thanks for that link. There is a wealth of information tether which I going through now.  Thanks again . 

Jim 

I didn't make as much progress today as I had hoped. I made a trip out (stay local)  to pick up another roll of aluminum tape and got lost in a few other distractions - snowing here today  Anyway, I cleaned out my old oil can (mgb can wait for its oil change until better weather) and cut the top off using tin snips.  As feared, the throat of the horn and the opening of the wave guide don't match in size exactly!  As this will be sitting in a classroom, being moved about, I'm keen to make it as robust as possible. With that in mind, I was toying with the idea of making a flange to attach the wave guide to the horn.  I have a laser cutter which I could use to cut 3mm ply to form the flange - the ply would then be covered in conductive Al tape.    My question is, how critical is it to have the cross sectional area of the transition from the horn to the waveguide constant ie no step changes ?   Hope that makes sense.   I would try to minimise the size of any step change but I thought I better ask before proceeding on blindly. 

Jim 

Thanks Ed astro, I was hoping that would be the case.

Jim 

Well , I didn't get as far on as I thought I would but that is the horn lined with the aluminium foil. What a nightmare trying to stop it from wrinkling .  I don't know how sensitive it will be to all the discontinuities but it looks ok.  I have some aluminium angle section that I'll use to brace the corners to give it a little structural support and to better hold its shape.  I'll make a start on the wave guide tomorrow. Lol there are foil off cuts and aluminium speed tape all over the kitchen. My darling wife was convinced that I was making a tin foil hat !

Jim 

Cheers Chris, I hope I live up to your kind words.  To be honest, I've always thought that you have to be pretty determined to muck up teaching Physics  - I've always thought of it as "the beautiful subject".  At its heart the subject has a very playful nature - that childlike sense of curiosity (let's put a bigger rocket motor in it )  ; for me, teaching Physics is a privilege - I get paid to play    Having said that, I turned 55 the other month so maybe I do need to start weaning myself off the skateboard ; I took out 3 chairs and a group of retort stands just before the Easter break  

Jim 

5 minutes ago, Corncrake said:

Thank you ! I can take a hint.

Chris , corncake and all , keep the advice coming  - like I said this really is the dark arts to me !  I'm not looking forward to the part where I have to shake the chicken bones and see where they land.  

Jim 

My connectors have just arrived together with some Aluminium conductive tape - "smoke on go".   The little black device is the low noise amp and the blue usb dongle is the SDR  decoder that connects to the laptop.   I'll need to solder a short length of copper wire into the coax connector to act as the dipole (not sure if that is the right term) - the detector of the wiggly RF amps !   

Here's the pdf showing the dims of the antena and general construction outline. 

Jim 

DSPIRA_Horn_Assembly.pdf

Thanks Corncrake. I had wondered if orientation of the Al foil would matter but couldn't think of any reason.  What you said makes sense so a longitudinal overlay it shall be.   I'll look to use the full width of the aluminium foil off the roll (about 350 mm) as far as I can - the diagram I put up was only a quick outline.  I know what you mean about the website the documents are scattered about, I'll post up the plan from the pdf with dimensions.  As far as portability is concerned I'll be happy so long as I can transport it in the car to school. Thereafter it's a short lift from the classroom to outside.  My thinking is that if I can get a useful result with this first attempt (foam board and tin foil) then I may invest in some aluminium sheet and do it all properly.  If I can use it to show the 21 cm hydrogen line and perhaps an idea of doppler shift then I'll be happy - it would fit nicely into our Higher Physics class work.  To be honest, this is a diversion - the kids have had a really rubbish year, as we all have,  so I'm just looking for something to lighten the load a little - and it will be so cool if we can do it     I also know absolutely nothing of radio propagation/antennas/reception/processing.  Waveguides, side lobes, ground clutter were only words the avionics technicians would use to hoodwink me in my RAF days.  So it's also a nice wee project to challenge me; hopefully I may even learn something.   Here's a photograph of where I am at the moment.  The gallon of oil container is due to become the wave-guide.  I need to decide where to put the oil !   I was supposed to do an oil change on my mgb  last month but put it off due to weather. If I can't find a spare container to decant the oil into then I guess I will have to bite the bullet and just put it in the car   Just waiting for the final delivery from Amazon, coax connector, and then I think that is me.  I would like to think I could test it sometime tomorrow.

Jim 

Apologies the diagram is pretty poor   

Jim 

Thanks Andrew. Using aluminium foil was my next question!  Looking on-line at the cost of aluminium sheet gave me a fright , particularly when delivery costs is added.  I think as you suggest I'll  use the boards that I bought as a backing and try gluing thick cooking foil to line them.  In terms of gluing the foil to the boards, I take it i will need to ensure  that each overlap section of foil would need to have continuity with the one it overlaps with . Hope that makes sense.  So I shouldn't use glue/paste on the underneath side of the overlap. I was planning to use aluminium tape to join the overlaps from the top - that way they will have electrical contact underneath !  Not a great explanation , maybe the diagram would be helpful. 

I bought an SDR usb dongle from AMAZON and have been playing around with it using AirSpy software - it came with a simple telescopic whip antenna so a bit limited but it was cool to pick up some mainstream stations. I'm sitting listening to a very noisy Classic FM through the laptop while next to me is a very capable Denon home entertainment amp with beautiful sound .  Isn't it strange that it's the simpler technology that is often more enjoyable     Anyway, I have a massive learning curve ahead ;  dipoles and wiggly amps and waterfall diagrams  is an area that is black magic to me .  I have an LNA  arriving tomorrow so I may be able to try a mock up by the weekend all being well. 

Jim 

Motivated by the recent posts on Hydrogen and Methanol line detection I thought that building a radio telescope would make a nice project for the classroom .  I'm looking to follow the open source design offered by DSPIRA .  In their build the horn is constructed from aluminiumized insulation board.  I was looking to do something similar and in the local B&Q store today I picked up what I thought would be suitable material in the form of a pack of aluminiumized faced underlay for hardwood flooring.  When I got it home though I've found that the reflective facing is actually something similar to mylar. I 've checked it with a multi meter and it's certainly not conductive .  Would I be right in thinking that this material would not be suitable for the horn ?

Jim 

 https://wvurail.org/dspira-lessons/tour/

6 minutes ago, ShrewView said:

Lovely. It makes me wonder though, who RC Stanley was and what happened in RM 417?

This could be the makings of a "J.R. Hartley" moment  

Jim 

for those to young to remember !

you wait until he realises he can produce a raster scan image and then we will get his advertising whether we like it or not. Even worse, he will sell it for hire to third parties.  Coca cola emblazoned across the night sky  

Jim

2 minutes ago, andrew s said:

Gardeners World (before its PC phase) used to advocate peeing on your compost heap.

Regards Andrew 

I'll may occasionally howl at the moon but that is a step too far  

Jim 

25 minutes ago, Paul M said:

From waste water? Although I'm in that industry my site doesn't do "P Removal" as it's lovingly known. A few years ago sites that are required to remove it were given a target that no known process could achieve at the time. I think the principal and the expenditure is there but the err, practice might still be "variable"!

It remains a feared determinand in environmental permits!

Here's the video Paul, the whole thing is worth watching but the section on Struvite production starts around 41 minutes in.  If you do watch it's worth rewinding and watching the section on supercooled Helium - it exhibits some amazing properties when supercooled.  

Jim 

Super Elements

I showed a video in class the other week and learned that  we recycle the phosphorus from our waste.  It's removed at water treatment plants then  goes back into crop fertilizers . Pretty ingenious , the things you learn in school  

Jim

I'm in the unlikely camp as well; I think it offers too much of an advantage even when energy is in plentiful supply. 

Jim