Radio Astronomy
Now that your observatory is ready for celestial viewing, you
are swamped by cloudy nights, what do you do? You start searching the internet
for alternative functions for you newly constructed retreat, that's what!
Radio astronomy is one of many such alternatives.
I know absolutely nothing about it, so after some dumb searching
through pictures, its time to start making stuff!
This iamge graphically illustrates that there is an alternative to visual astronomy
I got this little antenna idea from another bloke on the net, to
listen to Jupiter and the sun via a little $50 short-wave receiver on around 21
MHz. As with most good sheds, mine has plenty of bits of
scrap materials for a project like this, stuffed in the gaps between all the hoarded junk!
The frame if the antenna is made of plastic electrical conduit.
You can bend it into shape with a hair drier. Be careful not to get one point
too hot under tension or it just folds! Cut the grey conduit approximately
219cm. Remember to account for the length of the wide end. Do a bit of Pi x D
and your circle diameter should be 70 cm. Bend it into a circle and slot one end
into the other. It will form an ellipse. Secure by drilling a hole through the
join and place a small gutter bolt through it.
Then all you do is lay it on a flat surface, and gently heat the
ring with the hair drier. As soon as you see it start to move, STOP heating it
and wait! Go slow and do it a bit at a time until it looks like a neat circle.
If you heat too much and it folds, un-join the ends, heat the fold and pull it
out straight. Then wait for it to cool and start again.
I used a thinner 20mm outdoors conduit for the ring because it
is very flexible. The four uprights (30 cm) and the centre supports are the
thicker 25mm underground stiff conduit. Be aware that you need to paint it or
the sun will destroy the orange stuff.
I cut slots out of the ends of the orange bits to admit the
diameter of the grey conduit. Then its just a simple matter of drilling a hole
through the other ends, cutting your copper wire to length (170 cm) and
feeding/bending it through to form the loop. Once you have the right diameter
(53cm) position the slotted ends over the grey loop, press down and get the
positions and angles right so that the wire loop is centered over the plastic
loop. Drill holes in the slot tabs and secure with small gutter bolts.
The mass concrete stump to hold the mast up must be stable enough to support it in all kinds of conditions from wind to waterlogged ground. The hole is now a decent depth int o compact hard clay matrix. For extra strength and stability beyond the depth of the concrete, I have belted in a steel stake and welded cross-bars onto it to grip the concrete.
The brown appendage you see on the end of the white mast will also be cemented in this hole, leaving just the tops poking out to bolt the mast on.
[HoleStake]
For the mounting point, cut two lengths of orange conduit, slot
both ends parallel and position equal distance apart, running top to bottom of
the antenna in the grey loop. Drill and secure with gutter bolts. Then drill
across the centre of both of them and slide a bolt (10mm or so), two washers and
two short pieces of orange conduit as spacers in between. Leave a gap in the
middle big enough to admit whatever size mast you are going to use. I just used
another short piece of orange conduit and later secured that to my mast.
For the reflective shield, use chicken mesh, bird wire, aviary
mesh or whatever works for you. Cut to shape and size of the grey ring and
secure to the inside with zip ties, twist ties or tape. Using 50 ohm coaxial
cable, strip back a good 40 cm of the black insulation. part the silver braid
near where you cut the insulation until you can grab the white plastic
insulation that protects the center wire. Use a pair of point nose pliers. Pull
the white wire through so you end up with a three way "Y" of coax, braid and
core. Solder the outer braid to the mesh and cut off any excess. Strip the tip
of the inner wire and solder to the copper ring. Neatly zip tie or tape the
cable along the conduit, making sure the antenna can swivel without pulling the
contacts off.
I want to be able to change the angle of the antenna from below
so I have attached a spring via a couple of small eye bolts, that will hold the
antenna horizontal until pulled vertical and tied via a string from the ground.
To change direction I will simply twist the mast.
Give it all a coat of whatever colour spray paint you like,
attach it to the mast and "Voila!", you're done!
Here's another I have had a go at. This one is a dipole cut for 21 mHz. The
plans can be found at this site. http://www.radiosky.com/jupant1.html
Here's the new antenna mast I have been welding up. Half done, half to go...