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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MIDI controlled fire drums

Using an MSA-T MIDI Decoder from Highly Liquid, [Rob Darman] was able to take the MIDI output of his Roland V-Drums and use that output to control fire shooting cannons, forming a setup that he calls fire drums. As seen in the video above, the response time between the V-Drums and the fire drums is pretty impressive. While this is by far one of the coolest things that we’ve seen controlled by MIDI, we’re naturally thinking about taking this to the next level; MIDI-controlled fireworks, anyone?

You may remember the MSA decoder devices from people wiring up MIDI drums to Rock Band.

MIDI drums for Guitar Hero and Rock Band

Embedded above is [egyokeo]’s solution for using MIDI drums with Guitar Hero. He’s playing a DrumKAT MIDI kit. It connects to a PC running his MIDI Hero software, which handles timing and multinote combinations. The PC uses a USB ToolStick microcontroller to send commands to the console using an FPS adapter or soldered into the instrument. It’s a fairly good solution if you’re building a generic controller and need to modify the signaling.

When Rock Band was first released, modders sought to adapt their MIDI drum kits for use with the game. The easiest solution they found was Highly Liquid’s MSA-P. It’s a photorelay based MIDI decoder. You need to solder directly to the brain in the Rock Band drums. If you’re planning on modding any instrument, check the compatibility matrix first. Hopefully you’ll end up with something that can be used across multiple games.

[via Gizmodo]