Retrotechtacular: Ma Bell’s Advanced Mobile Phone Service (AMPS)

This gem from the AT&T Archive does a good job of explaining the first-generation cellular technology that AT&T called Advanced Mobile Phone Service (AMPS). The hexagon-cellular network design was first conceived at Bell Labs in 1947. After a couple of decades spent pestering the FCC, AT&T was awarded the 850MHz band in the late 1970s. It was this decision coupled with the decades worth of Bell System technical improvements that gave cellular technology the bandwidth and power to really come into its own.

AT&T’s primary goals for the AMPS network were threefold: to provide more service to more people, to improve service quality, and to lower the cost to subscribers. Early mobile network design gave us the Mobile Service Area, or MSA. Each high-elevation transmitter could serve a 20-mile radius of subscribers, a range which constituted one MSA. In the mid-1940s, only 21 channels could be used in the 35MHz and 150MHz band allocations. The 450MHz band was introduced in 1952, provided another 12 channels.

repeated channelsThe FCC’s allocation opened a whopping 666 channels in the neighborhood of 850MHz. Bell Labs’ hexagonal innovation sub-divided the MSAs into cells, each with a radius of up to ten miles.

The film explains quite well that in this arrangement, each cell set of seven can utilize all 666 channels. Cells adjacent to each other in the set must use different channels, but any cell at least 100 miles away can use the same channels. Furthermore, cells can be subdivided or split. Duplicate frequencies are dealt with through the FM capture effect in which the weaker signal is suppressed.

Those Bell System technical improvements facilitated the electronic switching that takes place between the Mobile Telephone Switching Office (MTSO) and the POTS landline network. They also realized the automatic control features required of the AMPS project, such as vehicle location and automatic channel assignment. The film concludes its lecture with step-by-step explanations of inbound and outbound call setup where a mobile device is concerned.

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Hackaday Links: November 9, 2012

Yeah, it’s like Twitter but actually cool

Thingiverse – still the best place on the Internet to find cool 3D models to print out – has gone all Web 3.0 with their new Dashboard feature. Basically, you can think of this as Thingiverse’s version of Twitter. The dashboard allows you to see the latest updates from people you like, follow people, categories, and tags, and check out your all-important ‘who’s following me’ stats. Yes, to the Hackaday crowd it may sound a little lame, but it’s a great way to winnow the (awesome) wheat from the (slightly less awesome) chaff.

Hey, we goofed. And not by using the same image twice

Remember when we jumped on the Occupy Thingiverse bandwagon? Well, there were questions about the Thingiverse Terms of Service and confusion that Makerbot actually owns everything uploaded to Thingiverse. That’s completely wrong according to Makerbot’s lawyer [Rich McCarthy]. The whole issue dealt with “Moral Rights or attribution” – a French legal doctrine that isn’t part of US law (or the law of any English-derived legal system as far as we can tell). Yeah, we goofed.

Now u cn snd SMS msgs wit n ‘ino & cell sheld

[Meir] sent in a cellular library for microcontroller projects that allows for simple sending and receiving of SMS messages. Yes, it’s been done before, but [Meir] hid all the hardware interaction with the cellular shield – a good design practice – to make the code nice and tidy.

And you thought PVC was bad…

Just in time for Thanksgiving, [Lou] shows us the fastest way to make mashed potatoes: an oxygen and propane powered potato gun. The build uses oxy and propane tanks you can pick up for a few bucks at any hardware store, steel pipe for the barrel, a grill igniter, and a few pipe fittings. It’s awesome, and we’ve got to hand it to [Lou] for this one. Now to build one and test it out on our indestructible test dummy.

It’s just like the Raspberry Pi! They’re that backordered!

Remember the Stellaris Launchpad, the very cool (and very inexpensive) ARM dev board put out by TI? Yeah, they’re shipping now. News of this comes from [Ryan Holtz] at Autodesk after the FedEx guy came knocking a few days ago. The good news is they’re shipping, the bad news is the price increased slightly to $13.

 

Going cellular with your Arduino projects

You can add a huge measure of extensibiltiy to a project by using a cellular connection. Anywhere the device can get service you can interact with it. In the past this has been a pretty deep slog through datasheets to get everything working, but this tutorial will show the basics of interacting with phone calls and text messages. It’s the 26th installment of what is becoming and mammoth Arduino series, and the first one in a set that works with the SM5100B cellular shield.

We love the words of warning at the top of the article which mention that a bit of bad code in your sketch could end up sending out a barrage of text messages, potentially costing you a bundle. But there’s plenty of details and if you follow along each step of the way we think you’ll come out fairly confident that you know what you’re doing. Just promise us that you won’t go out and steal SIM cards to use with your next project. Find part two of the tutorial here and keep your eyes open for future installments.

Chumby One becomes a 3g router

[bunnie] has taken a few moments to show us how to turn our Chumby One into a 3g router. As it turns out, there is an easter egg that allows it to communicate with certain models of 3g dongles. There’s no GUI for this trick, so you’ll be doing most of your configuration via SSH. That shouldn’t be a problem for this crowd though. The Chumby One just got a lot more appealing.

Cellular automata and LED matrix fun

Blinkomat, an LED matrix, turned out quite well. 240 LEDs controlled by an Atmega 16 is what we call a decent bookshelf decoration. The dimensions of 12×20 were chosen due to the fact that the microcontroller has 32 I/O lines.  The LEDs are switched on and off using multiplexing. The brightness, controlled by pulse width modulation can be varied by 16 levels.  The overall effect is quite smooth an fun to look at.  He has programmed it to do other things than just cellular automata.  Our personal favorite is a simple sine wave. Watch it after the break.

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