Wednesday, June 2, 2010

Chapter 5 - Exercise 31


So we're going to build an AM radio with an empty bottle, lots of wire, a germanium diode, and a cheap earphone... sounds fun.

A few things - I didn't have a 3" diameter bottle, but a 2.5" Flinstone's Vitamins bottle, generously donated by my 3 year old son who allowed me to put the remaining vitamins in ziploc bag. Thanks, D!

After removing the label and cleaning the bottle, I drilled the holes as instructed. It's hard to tell from Figure 5-60 how tall that bottle is but I don't think my bottle is tall enough to hold the 12 "taps" that the instructions say to build... and because the bottle's diameter is less than 3", I multiplied by the 16 to get a 40" distance between taps. Doing a little math, I quickly figured out that 12 taps wasn't going to wrap around once I got started...

BTW, start at the bottom of the bottle and work your way up - it's easier to tie off the wire when you're done wrapping if the holes near the top are exposed - I managed to get my fingers through the bottle opening and get it tied off. The author recommends 22 gauge wire, solid core... I used insulated and I'm glad I did... makes it much easier to wrap and you'll save your fingers from wire-burn... yes, I made that term up, but exposed wire does get hot to your fingers when you're wrapping... your call.

After wrapping my bottle tightly, I managed to get 10 taps before running out of room... I don't think this will be an issue but may give me fewer chances of success when it comes to picking up a signal. As you can see, my taps aren't spaced as far apart as the author's are in Figure 5-64... crossing my fingers and hoping.

Up next, getting the antennae setup... I've got the germanium diode and earphone, so I need to get some rope that won't interfere with the antenane and keep it from grounding... more to come.

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