Build Your Own Radio Clock Transmitter

NIST

Deep in the Colorado foothills, there are two radio transmitters that control the time on millions of clocks all across North America. It’s WWVB, the NIST time signal radio station that sends the time from several atomic clocks over the airwaves to radio controlled clocks across the continent. You might think replicating a 70 kW, multi-million dollar radio transmitter to set your own clock might be out of reach, but with a single ATtiny45, just about everything is possible.

Even though WWVB has enough power to set clocks in LA, New York, and the far reaches of Canada, even a pitifully underpowered transmitter – such as a microcontroller with a long wire attached to a pin PWMing at 60kHz – will be more than enough to overpower the official signal and set a custom time on a WWVB-controlled clock. This signal must be modulated, of course, and the most common radio controlled clocks use an extremely simple amplitude modulation that can be easily replicated by changing the duty cycle of the carrier. After that, it’s a simple matter of encoding the time signal.

The end result of this build is an extremely small one-chip device that can change the time of any remote-controlled clock. We can guess this would be useful if your radio controlled clock isn’t receiving a signal for some reason, but the fact that April 1st is just a few days away gives us a much, much better idea.

TDOA (Time Difference of Arrival) Directional Antenna

tdoa-antenna-tutorial

We have posted articles in the past on directional antennas such as Yagi antennas used for transmitter hunting otherwise known as fox hunting. Those types of antennas and reception suffer from one major drawback, which is as you get close to the transmitter the S meter will go full scale. At which time the transmitted signal appears to be coming from all directions. To correct for this problem you need to use clever signal attenuators or change to a poor receiving antenna as well as tuning off frequency effectively making your receiver hard of hearing so that only the direct path to the transmitter is loudest.

There is another popular type of antenna that you can build yourself called a TDOA which stands for Time Difference of Arrival. [Byon Garrabrant N6BG]  shared a short video tutorial on the functionality of his home built TDOA antenna. Effectively this is an active antenna that uses a 555 chip or, in [Byon’s] case, a PIC chip to quickly shift between two receiving dipole antennas at either end of a shortened yardstick. In his explanation you learn that as the antenna ends move closer or farther from the source a 640 Hz generated audio tone will go from loud to very soft as the antennas become equal distance from the source. This type of directional reception is not affected by signal strength. This means you can be very close to a powerful transmitter and it will still function as a good directional antenna.

The current circuit diagram, BOM and source code are all available on [Byon’s] TDOA page.

The reason [Byon] used a programmable PIC instead of the 555 for his design is because he wants to add a few more modifications such as feeding back the audio output to the PIC in order to programmatically turn on a left or right LED indicating the direction of the transmitter. Furthermore, he plans on adding a third antenna in a triangular configuration to programmatically control a circle of 6 LEDs indicating the exact direction of the signal. When he finishes the final modifications he can drive around with the antenna array on his vehicle and the circle of LEDs inside indicating the exact direction to navigate.

We look forward to seeing the rest of the development which might even become a kit someday. You can watch [Byon’s] TDOA video after the break.

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Verifying A Wireless Protocol With RTLSDR

rtlsdr_nrf905_rtlizer

[Texane] is developing a system to monitor his garage door from his apartment. Being seven floors apart, running wires between the door and apartment wasn’t an option, so he turned to a wireless solution. Testing this wireless hardware in an apartment is no problem, but testing it in situ is a little more difficult. For that, he turned to software defined radio with an RTLSDR dongle.

The hardware for this project is based around a TI Stellaris board and a PTR8000 radio module. All the code for this project was written from scratch (Github here), making it questionable if the code worked on the first try. To test his code, [Texane] picked up one of those USB TV tuner dongles based around the RTL2832U chipset. This allowed him to monitor the frequencies around 433MHz for the packets his hardware should be sending.

After that, the only thing left to do was to write a frame decoder for his radio module. Luckily, the datasheet for the module made this task easy.

[Texane] has a frame decoder for the NRF905 radio module available in his Git. It’s not quite ready for serious applications, but for testing a simple radio link it’s more than enough.

Build a Cheap Airplane ADS-B Radio Receiving Tracking Station

airplane tracking with ADS-B radio receiving

Do you have commercial or general aviation flying over your home or near your home? Would you like to know more about these airplanes: identity, heading, speed, altitude and maybe GPS data along with even more information? Well then [Rich Osgood] has just the project for you and it’s not that expensive to set up. [Rick] demonstrates using a cheap USB dongle European TV tuner style SDR (software defined radio) tuner that you can get for under $30 to listen in on the Automatic Dependent Surveillance-Broadcast (ADS-B) 1090 MHz mode “S” or 978 MHz mode “UAT” signals being regularly transmitted from these aircraft.

He steps us through configuring the radio to use a better antenna for improved reception then walks through detailed software installation and set up to control the radio receiver as well as pushing the final decoded data to mapping software. This looks like a fascinating and fun project if you live near commercial airways. You won’t need a license for this hack because you’re only listening and not transmitting, plus these are open channels which are legal to receive.

There are some frequencies you are not legally allowed to eavesdrop on—private communications for residential wireless telephones and cellular frequencies to name just a few (Code of Federal Regulations Title 47, Part 15.9). So remember you do have to be careful and stay within legal frequencies even if your equipment is not restricted from such reception. Also note that just because you have a legal right to intercept conversations or data on some frequencies it could be illegal to publicly share the intercepted content or any details on the reception or decoding (just saying for the record).

We wonder if [Rick] could partner with [G. Eric Rogers] to upgrade [Eric’s] motorized telescope airplane tracking system to extrapolate the radio telemeter data into vector data so his Arduino can track without relying on a video feed. That merger might just get them both on a short TSA list.

Join us after the break for some extra informational links and to watch the video on setup, installation and usage of this cheap airplane tracking rig.

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Tape Measure VHF Yagi Antenna

tap measure yagi vhf antenna

Radio direction finding and fox hunting can be great fun and is a popular activity with amateur radio (ham radio) enthusiasts. These antennas are great and are not only good for finding transmitters but also will greatly increase directional distance performance including communicating with satellites and the international space station (ISS).

[jcoman] had a nephew who was interested in learning about amateur radio so [jcoman] figured building and using a cheap and portable 2 meter band VHF Yagi style beam antenna would be the perfect activity to captivate the young lad’s interest in the hobby.

His design is based on [Joe Leggio’s] (WB2HOL) design with some of his own calculated alterations. We have seen DIY Yagi antenna designs before but what makes this construction so interesting is that the elements come together using bits of cut metal tape measure sections. These tape measure sections allow the Yagi antenna, which is normally a large and cumbersome device, to be easily stowed in a vehicle or backpack. When the antenna is needed, the tape measure sections naturally unfold and function extremely well with a 7 dB directional gain and can be adjusted to get a 1:1 SWR at any desired 2 m frequency.

The other unique feature is that the antenna can be constructed for under $20 if you actually purchase the materials. The cost would be even less if you salvage an old tape measure. You might even have the PVC pipes, hose clamps and wire lying around making the construction nearly free.

We were quite surprised to find that such a popular antenna construction method using tape measure elements had not yet been featured on Hackaday. For completeness this is not the only DIY tape measure Yagi on Instructables so also check out [FN64's] 2 m band “Radio Direction Finding Antenna for VHF” and [manuka’s] 70 cm band “433 MHz tape measure UHF antenna” postings. The other Yagi antenna designs featured on Hackaday were “Building a Yagi Uda Antenna” and “Turning an Easter Egg Hunt into a Fox Hunt” but these designs were not so simple to construct nor as cleverly portable.

A DIY NFC Tag

Simple NFC Tag

[Nicholas] built a simple NFC tag using an ATtiny84 microcontroller, four resistors, three capacitors, a diode, and an antenna. It implements ISO 14443-3, a standard for identification cards, and can communicate with the NFC chip sets found in most new smartphones.

This standard uses on-off keying for communication, which makes the hardware slightly more complex than the AVR RFID tag that we saw a few years back. The antenna and a variable capacitor form an LC circuit tuned at 13.56 MHz, which is the carrier frequency for the protocol. The diode acts as an envelope detector, letting the microcontroller recover the signal.

It may not be fully compliant with the standard, but [Nicolas] successfully tested out the device with his Lumia 620 phone. The firmware is available on Google Code so you can program your own tag data into main.c, build the firmware, and send some NFC packets. You can also check out a demo of the device after the break.

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BITX, A Return to Hackers’ Paradise

bitx

[Bill Meara] has finished up his radio. It both looks and sounds great. It was only a few weeks ago that [Bill] posted a guest rant here on Hackaday. The Radio he mentioned building in the rant is now complete. The transceiver itself is a BITX, a 14MHz Single Sideband (SSB) radio designed by Ashhar Farhan VU2ESE. Ashhar designed the BITX as a cheap to build, and easy to tune up transceiver for radio amateurs in India.

By utilizing parts easily sourced from scrapped TV sets, the BITX can be built for less than 300 Indian Rupee – or about $4.70 USD. In [Bill]’s own words, “Five bucks and some sweat equity gets you a device capable of worldwide communication.” He’s not kidding either. [Bill’s] first QSO was with a ham in the Azores Islands of Portugal.

[Bill] built his radio using the “Manhattan” building style, which we’ve seen before. Manhattan style uses rectangular pads glued down onto a copper ground plane. It makes for a more flexible design than regular old dead bug style building. Looking at all those components may be a bit daunting at first, but plenty of support is available. [Bill] has an 18 part build log on the soldersmoke website. There also is an active yahoo group dedicated to the BITX.