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N3 SDR Receiver

Sure, you can drive a nail into a board using a brick, but the whole time you're doing it, you know it's not right.

The same thing went through our minds every time we plugged in a Generation 1 or Generation 2 ThumbNet dongle. It feels a little wrong to use a circuit designed for TV reception for Software Defined Radio.

We went back to the drawing board, got a clean sheet of paper and designed an entirely new, next generation circuit that is completely compatible with existing SDR software and hardware.

We like to push the edge of what's possible.

Introducing the ThumbNet N3 SDR Receiver.

The next Generation, ThumbNet N3 is designed from the ground up to be as simple to use as older generation dongles, but with powerful hardware features for advanced hobbyists and experimenters.

We removed all of the excess components that were sources of noise or interference in other dongles, and optimized the circuit for simplicity, sensitivity and selectivity. Then we added a port to use a cable with the extremely common mini-USB connection so that the N3 is less prone to noise from the host computer than a traditional dongle. Finally, the use of standard Surface Mount 0603 or larger components makes it simple for testing or modification.

We built them for our own use, then decided to offer them to everyone.

The N3 works like other RTL-SDRs, but with siginificantly better performance. This higher performance consumes a little more current, so please ensure that your USB port can provide at least 410mA. Alternatively, use an external 5V (max 6V, min 4.5V) power supply (5V, 1000mA linear supplies are available in the Nongles Store ). A Phoenix plug with screw terminals is provided for this purpose.

It is advised that the user wire directly to the Phoenix plug (check polarity and for loose wires that may cause a short-circuit) and insert or remove the plug whenever you want to connect power to the N3 instead of removing the wires from the plug each time.

A quick list of the features of the N3:

- Full backward compatibility with existing RTL-SDR dongles and software
- High stability TCXO (+/-0.5ppm) (ensuring rock-solid stability from start-up and over a wide range of temperatures)
- Standard R820T2 + RTL2832U (plus 24C02 EEPROM) chipset (24 MHz to 1766 MHZ)
- Improved/enhanced decoupling. (Common-mode choke on USB port)
- Low-noise, linear only power regulation (separate 1.2v and 3.3v regulators)
- External DC +5v supply connector (included)
- Mini-USB connection (allows easy separation of the RF unit from the noisy PC)
- F type RF connector (very common and compatible with existing ThumbNet tracking stations)
- Large (6x4cm) contiguous ground-plane (for better thermal dissipation)
- Static drain-away resistor on the RF input (1K to ground)
- All unnecessary parts (IR receiver, high-current LED etc.) eliminated to reduce parts count and noise

Ideal for experimentation:

- Can be connected to an external power supply for very clean power
- All of the important tracks are visible on the top side of the board for easy access
- All of the RF parts are on the top of the board (only regulators and decouplers on the back)
- Logical, simple layout using 0603 (or larger) SMT parts
- IF port break in connector (between front end and IF/USB chip) provided

Utilizing Clean Power

While not required for operation, the N3 receiver is designed to be able to utilize a clean source of power from an external 5v power supply, instead of using the noisy power line coming from the computer's USB port. This gives a tremendous advantage to the purist or experimenter who wants to utilize power from the N3 to power any external experiments. (When the external power supply is active, no power is drawn from the USB port to power the N3.)

PLEASE NOTE: The N3 draws approximately 410 milliamps of current and care should be taken, even when using a powered USB hub, as it could possibly exceed the current limit of the USB port. (5v 1000mA linear power supplies are available in the Nongles Store ).

Supporting a Great Cause

Proceeds from the sale of the N3 SDR Receiver are used to support ThumbNet, the non-profit organization that is helping students around the world learn about Science, Technology, Engineering and Math (STEM) as well as Space, Radio, Meteorology and even Art. All at the same time!

You can read more about ThumbNet here, but to summarize: ThumbNet was born to encourage students around the world to look up at the stars and to give them a chance to feel that they are part of something larger. The hardware to track and monitor radio signals from satellites in orbit is donated to the schools by ThumbNet, and with over 200 volunteer groups in more than 72 countries, we're having an immediate and positive effect on the lives of hundreds of students around the globe! ThumbNet averages three new volunteer groups a week, so when you buy an N3 receiver for your workshop, you'll know that you're making a difference by supporting a global effort to educate and inspire students.

We've designed the N3 receiver to be the right tool for the job for our ThumbNet volunteers, and at only $25.75 each, we think you'll agree that it's the right tool for you too!