Radio Hacks

1333 Articles

RF Noise Floor Concerns From Both Sides Of The Atlantic

July 20, 2017 by 47 Comments

Our feed is full of stories about the RF noise floor today, and with good reason. The ARRL reports on the International Amateur Radio Union Region 1 president, [Don Beattie, G3BJ] warning that in densely populated parts of Europe there is a danger that parts of the RF spectrum have become so swamped with noise as to be rendered unusable, while on the other side of the Atlantic we have RadioWorld reporting on similar problems facing AM broadcasting in the USA.

At issue are the usual suspects, interference from poorly shielded or suppressed domestic electronic devices, VDSL broadband, power-over-Ethernet, solar and wind power systems, and a host of other RF-spewing electronics. The combined emissions from all these sources have raised the noise level at some frequencies to the point at which it conceals all but the strongest signals. Any radio amateur will tell you that a station in a rural location will be electrically much quieter than one in a city, it seems that this effect has now reached a crescendo.

In the RadioWorld article, the author [Tom F. King] and his collaborator [Jack Sellmeyer] detail a series of tests they performed on a selection of lighting products from a quality brand, bought at a local Home Depot store. They were gathering data for a submission to the FCC enquiry on the noise floor issue we reported on last year. What they found was unsurprising, significant emissions from all the products they tested. They make some stiff recommendations to the FCC and other bodies concerned with radio spectrum to get tough with offending devices, to stay on top of future developments, and for operators of AM stations to pursue sources of interference.

It could be that there is so much equipment contributing to the noise floor that this battle is lost, but it doesn’t have to be this way. Anyone who has had to prepare a product to pass a properly carried out EMC test will tell you that the requirements are stringent, and it is thus obvious that many manufacturers are shipping products unworthy of the certification they display. It is to be hoped that the authorities will begin to take it seriously before it becomes an order of magnitude worse.

Compliance label image, Moppet65535 [CC BY-SA 3.0].

Paul Horowitz And The Search For Extra Terrestrial Intelligence

July 19, 2017 by 91 Comments

I recently had the opportunity to attend a lecture by Harvard Professor Paul Horowitz. It’s a name you likely recognize. He is best known for his iconic book the Art of Electronics which is often referred to not by its name but by the last names of the authors: “Horowitz and Hill”.

Beyond that, what do you know about Paul Horowitz? Paul is an electrical engineer and physicist and Paul has spent much of his storied career learning and practicing electronics for the purpose of finding intelligent extra terrestrial life.

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Flush Out Car Thieves With A Key Fob Jammer Locator

July 16, 2017 by 97 Comments

We all do it — park our cars, thumb the lock button on the key fob, and trust that our ride will be there when we get back. But there could be evildoers lurking in that parking lot, preventing you from locking up by using a powerful RF jammer. If you want to be sure your car is safe, you might want to scan the lot with a Raspberry Pi and SDR jammer range finder.

Inspired by a recent post featuring a simple jammer detector, [mikeh69] decide to build something that would provide more directional information. His jammer locator consists of an SDR dongle and a Raspberry Pi. The SDR is set to listen to the band used by key fobs for the continuous, strong emissions you’d expect from a jammer, and the Pi generates a tone that varies relative to signal strength. In theory you could walk through a parking lot until you get the strongest signal and locate the bad guys. We can’t say we’d recommend confronting anyone based on this information, but at least you’d know your car is at risk.

We’d venture a guess that a directional antenna would make the search much easier than the whip shown. In that case, brushing up on Yagi-Uda antenna basics might be a good idea.

Hackaday Prize Entry: Open Narrowband RF Transceiver

July 14, 2017 by 5 Comments

We have so many options when we wish to add wireless control to our devices, as technology has delivered a stream of inexpensive devices and breakout boards for our experimentation. A few dollars will secure you all your wireless needs, it seems almost whatever your chosen frequency or protocol. There is a problem with this boundless availability though, they can often be rather opaque and leave their users only with what their onboard firmware chooses to present.

The Open Narrowband RF Transceiver from [Samuel Žák] promises deliver something more useful to the experimenter: an RF transceiver for the 868 or 915MHz allocations with full control over all transmission parameters. Transmission characteristics such as frequency, bandwidth, and deviation can be adjusted, and the modulation and encoding schemes can also be brought under full control. Where a conventional module might simply offer on-off keying or frequency shift keying, this module can be programmed to deliver any modulation scheme its chipset is capable of. Spread-spectrum? No problem!

Onboard, the device uses the TI CC1120 transceiver chip, paired with the CC1190 front end and range extender. Overseeing it all is an ST Microelectronics STM32F051 microcontroller, which as you might expect is fully accessible to programmers. Interfaces are either USB, through an FTDI serial chip, or directly via a serial port.

There are a host of transceiver chips on the market which just beg to be exploited, so it is very good indeed to see a board like this one. It’s worth noting though that the CC1120 has a much wider frequency band than that of the CC1190, and with a different front end and PA circuitry, this could cover other allocations including some amateur bands.

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Rescuing A Proprietary Battery Pack With A Cell From A Camera

July 11, 2017 by 9 Comments

If you have an older handheld battery-powered device, you may be fighting a diminishing battery capacity as its lithium-ion cells reach the end of their life. And if you are like [Foxx D’Gamma], whose device is an Alinco DJ-C7 handheld transceiver, you face the complete lack of availability of replacement battery packs. All is not lost though, because as he explains in the video below the break, he noticed that a digital camera battery uses a very similar-sized cell, and was able to graft the camera battery into the shell of the Alinco pack.

Cracking open the Alinco pack, he was rewarded with the rectangular Li-Ion cell and two PCBs, one for the connector and another for the battery management circuitry. By comparison the camera battery had a much smaller battery management PCB, and it fit neatly into the space vacated by the Alinco cell once those covers had been removed. A fiddly soldering job to attach the connector PCB, and he was rewarded with a working Alinco pack and an unexpected bonus when he found out that the transceiver was a dual band model.

Along the way he’s at pains to point out the safety aspects of handling Li-Ion cells, and to ensure that the polarity of the cell is correct. It’s also worth our reminding readers that these packs must always be accompanied by their battery management circuitry. The result though is pleasing: a redundant piece of equipment made obsolete by a proprietary battery, given a new lease on life.

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Old Rabbit Ears Optimized For Weather Satellite Downlink

July 10, 2017 by 10 Comments

Communicating with a satellite seems like something that should take a lot of equipment. A fancy antenna and racks full of receivers, filters, and amplifiers would seem to be the entry-level suite of gear. But listening to a weather satellite with an old pair of rabbit ears and an SDR dongle? That’s a thing too.

There was a time when a pair of rabbit ears accompanied every new TV. Those days are gone, but [Thomas Cholakov (N1SPY)] managed to find one of the old TV dipoles in his garage, complete with 300-ohm twinlead and spade connectors. He put it to work listening to a NOAA weather satellite on 137 MHz by configuring it in a horizontal V-dipole arrangement. The antenna legs are spread about 120° apart and adjusted to about 20.5 inches (52 cm) length each. The length makes the antenna resonant at the right frequency, the vee shape makes the radiation pattern nearly circular, and the horizontal polarization excludes signals from the nearby FM broadcast band and directs the pattern skyward. [Thomas] doesn’t mention how he matched the antenna’s impedance to the SDR, but there appears to be some sort of balun in the video below. The satellite signal is decoded and displayed in real time with surprisingly good results.

Itching to listen to satellites but don’t have any rabbit ears? No problem — just go find a cooking pot and get to it.

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Horns Across America: The AT&T Long Lines Network

July 10, 2017 by 83 Comments

A bewildering amount of engineering was thrown at the various challenges presented to the United States by the end of World War II and the beginning of the Cold War. From the Interstate Highway System to the population shift from cities to suburbs, infrastructure of all types was being constructed at a rapid pace, fueled by reasonable assessments of extant and future threats seasoned with a dash of paranoia, and funded by bulging federal coffers due to post-war prosperity and booming populations. No project seemed too big, and each pushed the bleeding edge of technology at the time.

Some of these critical infrastructure projects have gone the way of the dodo, supplanted by newer technologies that rendered them obsolete. Relics of these projects still dot the American landscape today, and are easy to find if you know where to look. One that always fascinated me was the network of microwave radio relay stations that once stitched the country together. From mountaintop to mountaintop, they stand silent and largely unattended, but they once buzzed with the business of a nation. Here’s how they came to be, and how they eventually made themselves relics.

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