Sunday, July 14, 2013
Here are some photos of the feed for our radio telescope that I built last month. Basically, a metal can is used as a waveguide for 21cm radiation (it supports a single TE mode at around 1420 MHz). The feed is placed lambda (guided)/4 from the back, and it itself lambda(free space)/4 long. The most important things here machining-wise (thanks to Mark at the Edgerton shop!) were the conical drill bit for drilling thin materials, and the center punch for aligning the screw holes for the coax connector. The can is to be connected to a horn antenna, and the output signal is fed to amplification stages and finally a software-defined USB dongle receiver.
Saturday, July 6, 2013
Last night I shined laser light onto the edge of a playing card in hopes of forming an interference pattern on my wall. (I believe Thomas Young also used a card in his initial interference experiments by using sunlight that had passed through a pinhole) The following is a brief account of what I saw. I don't have any quantitative results on this yet, but will try to work out details in a later post. In principle it should be easily possible to measure the wavelength of light with this setup, or assume the wavelength (it is 650 nm) and measure the thickness of the card. (Of course we might as well measure the thickness of a deck and divide by 52 !)
Here are some pictures of the setup. The red laser pointer is mounted on a mini tripod while the card is held up by a slit cut into a cardboard box. The idea is that the card splits the laser beam into two beams which can interfere with each-other.
|Image 1: Card splitting a beam of laser light|
|Image 2: Other view|
The beam is deflected horizontally (perpendicular to the card) as can be seen in the distance.
|Image 3: Back view|
|Image 4: Lights out|
Here's a closer look at the wall, notice that the fringes on the left are different than those on the right. There seems to be a much longer spacing between nulls on the RHS.
|Image 5: Pattern observed on wall, notice differences between RHS and LHS|
|Image 6. LHS image from one of my attempts, looks like fairly even spacing. Can see variation in height of fringes.|
|Image 7: Close look at the LHS from another attempt|
An attempt at measuring spacing between the maxima (of image 7)