Forrest Mims Engineer’s Notebook: Communications Projects

A family friend gave us this Apple IIe computer as my dad told him about all the books I read but no real computer at home. It has a digitizer pad, very large like half my desk space. They used it for tracing building prints, but it was too old for them and the disk drive wore out so they decided to get a very expensive PC-compatible system to replace it. I had other Apple IIe parts that my middle school gave me for fixing their computers when they upgraded to Apple IIgs.

We had a few weeks of a guest teacher computer class, but it was kind of funny because I knew as much as the teacher about computers or at least what he was teaching on. I still don’t think anyone cared too much about it. It was really a class on using computers and not building or programming them, so I was kind of glad it ended. I have read every book at the library on computers plus several more on inter-library loan.

I started to checkout more electronics books. A lot of them were on vacuum tubes and there is a lot of stuff out there with vacuum tubes still. If you don’t turn them on and off too much, the tubes just seem to last forever. This is partly because the glowing filament is at a much lower temperature than light bulbs, so it’s not so stressed by temperature changes. I like the smell made by my dad’s shop AM/FM tube radio, it’s dust and oil and heat of the tubes. It also sounds a lot better than modern radios. Although I do like that I can carry transistor radios around!

My favorite time of all with Grandma is taking her radio out to the porch in the evening and listening to far away AM stations. We hear sports games and country music. I close my eyes as I hear the stations warbling in and out, sometimes hearing a mix of signals with a tremolo effect. It is a very relaxing thing as at night out here you can see for miles, it’s that time of year when planting is done and harvesting hasn’t begun. Things are just growing–you can hear the cornstalks crackling later in the summer.

So the main thing is these Forrest Mims Notebooks have a topic in each book. This communications book shows how to make a radio transmitter with a 9 volt battery and metal file. Well I knew already turning a light on and off could be heard in the AM radio tuned to any channel. I noticed that the lower frequencies on the AM radio say below 1200 kHz or so tend to go very far at night. The frequencies from 1200 kHz to 1600 kHz are just a jumble of noise at night. It’s voices but so many of them we can’t even hear stations 20 miles away at night on those upper AM band channels. I think this must be a legal matter, maybe there are many stations allowed on the upper AM band frequencies and fewer on the lower frequencies.

The other thing I notice is that on the FM band, you either hear one station or the other. Sometimes I hear stations from hundreds of miles away on the FM band but it seems to be mostly in the summer when the weather is changing. It doesn’t happen every day though.

I ran out of things I could do with my chemistry sets, at least with chemicals that are mostly safe. Electronics I can explore without making things too smelly or dangerous unlike chemistry. The biggest thing I would like to find is someone who is interested in the same things. If I can communicate on the radio, maybe I can find someone else interest in science and building things. It would be a lot less lonely.

The Mims book also shows a lightwave voice transmitter and receiver. I could build an intercom between the barn and house maybe. Or I could just flash the light in a pattern to make a bell ring maybe. These walkie talkies I have just make a constant screech when no one’s talking so that’s no good. The guy at the TV shop says it’s because they’re regenerative receivers and they don’t have a “squelch”. It seems kind of magical that you could make a radio that knows when someone is talking and is quiet when they’re not. The AM/FM radios also just make static but not a loud screech.

He said the cool thing about the walkie talkie regenerative receiver is that I can hear more than one channel at once. That seems good until you realize it’s only the strongest signal that you can hear and the others are mumbling in the background. I will try to get a better non-regenerative receiver this summer maybe.