A beacon is an intentionally conspicuous device designed to attract attention to a specific location. Beacons can also provide important information about their situation.
In this case, I made a beacon that transmits radio signals in a specific protocol named JT4. This protocol was invented by Joe Taylor and it is capable of transmit and receive messages with very low levels of signal, and low signal noise ratio (SNR). JT4 is included into the Weak Signal Joe Taylor protocol (WSJT) of the astrophysicist and Nobel Prize in Physics laureate.
This beacon will be part of a global net of beacons like it, that will be emitting their localization in the world in a specific frequency. In your home, or where you like, you will be able to receive the signal of a few beacons. Then you will know the localization of beacons that you can receive the signal and those you can not receive. Maybe one day you will receive ones, and in other moment you will receive another ones.
A group of people that like you, will be acquiring signals, and another that will be in other frequencies can upload everything to a online server on internet. With all of these data you can make a real time map about the propagation of the atmosphere related to each frequency of transmission.
There are studies about the radio propagation across the air, and it is known that it depends of the temperature, the humidity, the electric charge, and other climatic factors. So knowing all of these data will open a new way to predict the weather forecast.
The project has 4 parts that are closely interconnected between them:
- The code and the protocol: It is C and will be able to codify text characters into the JT4 codification. Also we want a graphic interface to introduce the text and configure the system. It will be run by a microcontroller.
- The modulation system. This will be done by a digital direct synthesizer (DDS). It is a device that requires a precise clock source for digitally generate a full sine output wave. It is programmable via serial port trough three wires.
- The synchronization. A GPS receptor will provide both UTC time (necessary for JT4 to known the start of each minute) and a 10Mhz precisely controlled clock, synchronized with GPS internal atomic clock.
- A radio receptor whose audio output is decompressed with the WSJT software to read the message transmitted.
Next is a schematic about the final structure:
A microcontroller ( Arduino UNO in this case) is used to manage all the data. As it will be an autonomous system you will be able to configure everything through the LCD and the microcontroller.
The GPS engine is a Rockwell 12-parallel channel Jupiter version T which is used for static use and timing/frequency aplications.The signal provided by the GPS (10kHz), that is also synchronized with the high precision clocks of the GPS satellites (atomic clocks) forms the base of an 10MHz local oscillator. As it is stabilized by an Oven (constant temperature) and it is in phase with the 10kHz signal of the GPS, we can obtain an 10MHz signal very very precise in short and long time.
Trimble provides a GPS disciplined clock module, known as thunderbolt. We have bought one that was recycled from an old communications beacon.
This 10MHz signal is used to clock the DDS, that requires it for digitally generate frequencies always lower than half the clock input based in Nyquist theorem. The DDS also have an internal clock multiplier that multiplies x6 the clock input used as frequency. So with our 10MHz provided by the GPS Oscillator, and multiplied by 6, we obtain an clock signal of 60 MHZ.
To be continued...