Hopefully by now most of us know better than to rent a modem from an internet service provider. Buying your own and using it is almost always an easy way to save some money, but even then these pieces of equipment won’t last forever. If you’re sitting on an older cable modem and thinking about tossing it in the garbage, there might be a way to repurpose it before it goes to the great workbench in the sky. [kc9umr] has a way of turning these devices into capable spectrum analyzers.
The spectrum analyzer feature is a crucial component of cable modems to help take advantage of the wide piece of spectrum that is available to them on the cable lines. With some of them it’s possible to access this feature directly by pointing a browser at it, but apparently some of them have a patch from the cable companies to limit access. By finding one that hasn’t had this patch applied it’s possible to access the spectrum analyzer, and once [kc9umr] attached some adapters and an antenna to his cable modem he was able to demonstrate it to great effect.
While it’s somewhat down to luck as to whether or not any given modem will grant access to this feature, for the ones that do it seems like a powerful and cheap tool. It’s agnostic to platform, so any computer on the network can access it easily, and compared to an RTL-SDR it has a wider range. There are some limitations, but for the price it can’t be beat which will cost under $50 in parts unless you happen to need two inputs like this analyzer .
Thanks to [Ezra] for the tip!
If your goal is to harvest unique parts from defunct devices, the further back in time you go, the better the pickings stand to be. At least that’s what [Kerry Wong] discovered during his tear-down of a darkroom color analyzer from the early 1980s.
For readers whose experience with photography has been solely digital, you need to understand that there once was a time when images were made with real cameras on real film, and serious amateurs and pros had darkrooms to process the film. Black and white processing was pretty straightforward in terms of chemistry — it was just developer, stop, and fixing. Color processes were much trickier, and when it came to enlarging your film onto color photo paper, things could get really complicated. [Kerry]’s eBay find, a Besler PM1A color analyzer, was intended to help out in the color lab by balancing the mix of cyan, blue, and yellow components in the enlarger.
The instrument, which no doubt demanded a princely sum back in the day, is actually really simple, with the object of [Kerry]’s desire, a PM1A photomultiplier tube and its driver, being the only real find. Still, it’s an interesting teardown, and we’re eager to see what [Kerry] makes of the gem. A muon detector, perhaps? An X-ray backscatter machine? Or perhaps repeating his old speed of light experiments is on the docket.
Continue reading “Tearing Down A Darkroom Relic For Buried Treasure”
Network Analyzers are frequently used for measuring filters, making them extremely valuable for building radios and general mucking about with RF. They are, however, extremely expensive. You can, however, build one in an Altoids tin with an Arduino Nano, a small screen, and an AD9850 frequency synthesis module picked up on eBay.
The basic idea behind a network analyzer is to feed a frequency into a device, and measure the amplitude coming out of the device, and plot this relationship over a frequency. [Bill Meara] has been a human network analyzer before, changing frequencies and plotting the output of devices under test by hand. [DuWayne] (KV4QB) build a device to automate the entire process.
The block diagram is easy enough – an AD9850 sends a signal to the device, and this is measured by the Arduino with a small amplifier. The signal is measured again when it comes back from the device under test, and all this is plotted on a small display. Simple, and [DuWayne] is getting some very good readings with a lowpass filter and crystal filter made on a small solderless breadboard.