Notes on Experiment 12

This experiment is pretty cool: if you get it to work right, you'll get a strong, clear signal. It's clear as day when everything is working; the output of my receiving antenna shot up to 4.5 volts when I pointed the transmitter at it.

Most of the construction was simple. Here are a few recommendations:

1. Definitely check that your amplifier is working before building the antenna! I didn't, and at first, life really sucked. You basically need to rebuild the circuit on the top of page 79. I checked this after I did everything else (and after I saw that it wasn't working), and it was a major pain in the ass. That was dumb on my part; learn from my stupidity.

2. The thing that I did wrong (and that I suspect many of you might do wrong) is to forget to hook all your zero point voltages up to ground. The reason that many of you will forget this is that it isn't shown in the circuit diagram on page 104. The negative input to the op-amp (socket 2) and the negative output lead both need to be grounded, as they were in Lab 10. If you don't do this, all your effort will seem to not work, and you will be very grumpy.

ADDENDUM: the missing ground in the circuit diagram is, in fact, noted in the Zap errata.

3. I found that it was easier to attach the capacitor and 1.2 megaohm resistors to the spark generator after soldering on two pieces of wire that make up the transmitting antenna. Once the other things were there, the pieces of thick copper wire didn't want to attach very well. (By the way, the wire you use for the antenna is not the brass rod you used to make the balance in Lab 9. The copper wire is darker and softer.)

The rest of construction is quite straightforward; if you get it to work, the subsequent analysis is fairly simple and qualitative. Feel free to email me if you've got questions.