Retro tech is cool. Retro tech that works is even cooler. When we can see technology working, hold it in our hand, and use it as though we’ve been transported back in time; that’s when we feel truly connected to history. To help others create small time anomalies of their own, [Dmitrii Eliuseev] put together a quick how-to for creating your own Advanced Mobile Phone System (AMPS) network which can bring some of the classic cellular heroes of yesterday back to life.
Few readers will be surprised to learn that this project is built on software defined radio (SDR) and the Osmocom-Analog project, which we’ve seen before used to create a more modern GSM network at EMF Camp. Past projects were based on LimeSDR, but here we see that USRP is just as easily supported. [Dmitrii] also provides a brief history of AMPS, including some of the reasons it persisted so long, until 2007! The system features a very large coverage area with relatively few towers and has surprisingly good audio quality. He also discusses its disadvantages, primarily that anyone with a scanner and the right know-how could tune to the analog voice frequencies and eavesdrop on conversations. That alone, we must admit, is a pretty strong case for retiring the system.
The article does note that there may be legal issues with running your own cell network, so be sure to check your local regulations. He also points out that AMPS is robust enough to work short-range with a dummy load instead of an antenna, which may help avoid regulatory issues. That being said, SDRs have opened up so many possibilities for what hackers can do with old wireless protocols. You can even go back to the time when pagers were king. Alternatively, if wired is more your thing, we can always recommend becoming your own dial-up ISP.
Most hobby-grade software defined radio setups don’t transmit. Of the few that do, most of them put out anemic levels around one milliwatt or so. If you want to do something outside of the lab, you’ll need an amplifier and that’s what [Tech Minds] shows how to do in a recent video. (Embedded below.)
The video covers LimeSDR, HackRF, and the Pluto SDR, although the amplifiers should work with any transmitter. The SPF5189Z module is quite cheap and covers 50 MHz to 4 GHz, amplifying everything you throw at it. The downside is that it will amplify everything you throw at it, even parts of the signal you don’t want, such as spurs and harmonics.
With the latest and greatest 5G cellular networks right around the corner, it can be difficult to believe that it wasn’t so long ago that cell phones relied on analog networks. They aren’t used anymore, but it might only take a visit to a swap meet or flea market to get your hands on some of this vintage hardware. Of course these phones of a bygone era aren’t just impractical due to their monstrous size compared to modern gear, but because analog cell networks have long since gone the way of the floppy disk.
But thanks to the efforts of [Andreas Eversberg] those antique cell phones may live again, even if it’s only within the radius of your local hackerspace. His software allows the user to create a functioning analog base station for several retro phone networks used in Europe and the United States, such as AMPS, TACS, NMT, Radiocom, and C450. You can go the old school route and do it with sound cards and physical radios, or you can fully embrace the 21st century and do it all through a Software Defined Radio (SDR); in either event, calls to the base station and even between multiple mobile devices is possible with relatively inexpensive hardware.
[Andreas] has put together exceptional documentation for this project, which starts with a walk through on how you can setup your DIY cell “tower” with traditional radios. He explains that amateur radios are a viable option for most of the frequencies used, and that he had early success with modifying second-hand taxi radios. He even mentions that the popular BaoFeng handheld radios can be used in a pinch, though not all the protocols will work due to distortion in the radio.
If you want to take the easy way out, [Andreas] also explains how to replace the radios with a single SDR device. This greatly simplifies the installation, and turns a whole bench full of radios and wires into something you can carry around in your pack if you were so inclined. His software has specific options to use the LimeSDR and LimeSDR-Mini, but you should be able to use other devices with a bit of experimentation.
It’s fair to say that software-defined radio represents the most significant advance in affordable radio equipment that we have seen over the last decade or so. Moving signal processing from purpose-built analogue hardware into the realm of software has opened up so many exciting possibilities in terms of what can be done both with more traditional modes of radio communication and with newer ones made possible only by the new technology.
It’s also fair to say that radio enthusiasts seeking a high-performance SDR would also have to be prepared with a hefty bank balance, as some of the components required to deliver software defined radios have been rather expensive. Thus the budget end of the market has been the preserve of radios using the limited baseband bandwidth of an existing analogue interface such as a computer sound card, or of happy accidents in driver hacking such as the discovery that the cheap and now-ubiquitous RTL2832 chipset digital TV receivers could function as an SDR receiver. Transmitting has been, and still is, more expensive.
A new generation of budget SDRs, as typified by today’s subject the LimeSDR Mini, have brought down the price of transmitting. This is the latest addition to the LimeSDR range of products, an SDR transceiver and FPGA development board in a USB stick format that uses the same Lime Microsystems LMS7002M at its heart as the existing LimeSDR USB, but with a lower specification. Chief among the changes are that there is only one receive and one transmit channel to the USB’s two each, the bandwidth of 30.72 MHz is halved, and the lower-end frequency range jumps from 100 kHz to 10 MHz. The most interesting lower figure associated with the Mini though is its price, with the early birds snapping it up for $99 — half that of its predecessor. (It’s now available on Kickstarter for $139.)
While most smartphones can receive at least some radio, transmitting radio signals is an entirely different matter. But, if you have an Android phone and a few antennas (and a ham radio license) it turns out that it is possible to get a respectable software-defined radio on your handset.
[Adrian] set this up to be fully portable as well, so he is running both the transceiver and the Android phone from a rechargeable battery bank. The transceiver is also an interesting miniaturized version of the LimeSDR, the Lime SDR Mini, a crowdfunded Open Source radio platform intended for applications where space is at a premium. It operates on the 10 MHz to 3.5 GHz bands, has two channels, and has a decent price tag too at under $100.
For someone looking for an SDR project or who needs something very portable and self-contained, this could be a great option. The code, firmware, and board layout files are all also open source, which is always a great feature. If you’re new to SDR though, there’s a classic project that will get you off the ground for even less effort.
A few weeks ago, the popcorn overflowed because of an ambiguous tweet from Adafruit. Did Adafruit just buy Radio Shack? While everyone else was foaming at the mouth, we called it unlikely. The smart money is that Adafruit just bought a few fancy stock certificates, incorporation papers, and other official-looking documents at the Radio Shack corporate auction a few months ago. They also didn’t pick up that monster cache of Trash-80s, but I digress.
Remember those 2D tilty maze rolling marble labyrinth game things? Here’s a 3D version on Kickstarter. It’s handheld, so this really needs a gimbal and associated twisty knobs.
In a video making the meme rounds, someone found an easter egg in the gauge cluster of a Russian GAZ van. It plays Tetris.
It’s Sunday, so it’s time to talk Star Trek. Here’s something interesting that hit my email: a press release telling me, “Trekkies Scramble To Get The First Toothbrush In Space As Seen On Star Trek Discovery”. This is the toothbrush, and here is the press kit. Dumb? Not at all. Star Trek has a long history of using off-the-shelf tools and devices for props. For example, the hyperspanners seen in Star Trek: Enterprise were actually this non-contact thermometer available from Harbor Freight. At least the hyperspanners and thermometers came out of the same injection mold.
Kerf bending is the application of (usually laser-cut) slots to bend plywood around corners. You’ve seen it a million times before, and done correctly the technique can produce some very interesting results. What about metal, though? You need a pretty big laser for that. [Proto G] is using a 2000 W fiber laser to experiment with kerf bending in stainless steel. It works as you would expect, and we eagerly await someone to replicate this, if only to see another 2000 Watt laser in action.
A few years ago, we saw the rise of software-defined radios with the HackRF One and the extraordinarily popular RTL-SDR USB TV tuner dongle. It’s been a few years, and technology is on a never-ending upwards crawl to smaller, cheaper, and more powerful widgets. Now, some of that innovation is making it to the world of software-defined radio. The LimeSDR Mini is out, and it’s the cheapest and most capable software defined radio yet. It’s available through a Crowd Supply campaign, with units shipping around the beginning of next year.
The specs for the LimeSDR mini are quite good, even when compared to kilobuck units from Ettus Research. The frequency range for the LimeSDR Mini is 10 MHz – 3.5 GHz, bandwidth is 30.72 MHz, with a 12-bit sample depth and 30.72 MSPS sample rate. The interface is USB 3.0 (the connector is male, and soldered to the board, but USB extension cables exist), and the LimeSDR is full duplex. That last bit is huge — the RTL-SDR can’t transmit at all, and even the HackRF is only half duplex. This enormous capability is thanks to the field programmable RF transceiver found in all of the LimeSDR boards. We first saw these a year or so ago, and now these boards are heading into the hands of hackers. Someone’s even building a femtocell out of a Lime board.
The major selling point for the LimeSDR is, of course, the price. The ‘early bird’ rewards for the Crowd Supply campaign disappeared quickly at $99, but there are still plenty available at $139. This is very inexpensive and very fun — on the Crowd Supply page, you can see a demo of a LimeSDR mini set up as an LTE base station, streaming video between two mobile phones. These are the golden days of hobbyist SDR.