Tagged: thumbsat

RTLSDR4Everyone: Preliminary Review of the ThumbNet N3 Prototype

A few weeks ago we posted about ThumbNets announcement of their new N3 RTL-SDR dongles. The main theme of their new dongles is lower noise as can be seen by their decision to disable the on board switch mode power supply and add an external power port for powering the dongle from a clean power supply.

Akos from the RTLSDR4Everyone blog received a prototype sample of the N3 for an initial review. In his review he shows some close up shots of the N3 PCB, and does a quick test on receiving some signals. His screenshots show that the noise floor is indeed very low, and that many noisy spurs are eliminated or at least significantly reduced.

Once ThumbNet release their actual commercial units we intend to produce our own review as well.

ThumbSat is a company hoping to enable experimenters to get low cost mini satellites into orbit for about $20k. To support the need for global RX of these satellites they have the ThumbNet project which utilizes RTL-SDR dongles as the receiver. They aim to provide schools and eligible volunteers around the world with free RX hardware to receive and record the data coming from these satellites.

Generic RTL-SDR and the ThumbNet N3


New ThumbNet RTL-SDR Receiver Released: F-Connector, TCXO, External DC Power, No Switch-Mode Power

ThumbSat is a company that aims to help experimenters design and launch experiments on their mini satellites (10x smaller than a regular cubesat with most of the same functionality) into orbit. They write that for about $20k they will fully design a satellite based experiment and launch it into orbit – all you need to do is provide the orbital experiment that you would like done.

To aide with the reception, they also have the ThumbNet project which aims to setup a network of satellite receivers around the world. They do this by providing school students around the world with low cost satellite receivers. The satellite receivers consist of modified/upgraded RTL-SDR dongles and satellite antennas. 

Today the ThumbNet project announced the latest iteration of their RTL-SDR dongle, called the ThumbNet N3 SDR Receiver. This receiver has some interesting design changes when compared to any other dongle that we’ve seen so far. The biggest change appears to be that this dongle uses an external power port for power. They also replaced the 1.2V switching regulator with a 1.2V linear regulator for lower noise operation. This is useful because switching regulators can cause noise, whilst linear regulators are much cleaner. However, using a linear regulator increases the power consumption significantly, and the new dongle draws 450mA of current (vs 250-280 mA on standard or our V3 dongles), meaning that some USB ports may be unable to power the device unless the external power supply port is used.

The other interesting change is that they have changed the PCB form factor, and it can now fit into a common 1455 aluminum case. Also, similarly to our V3 RTL-SDR dongles, they have decided to add a common mode choke to the USB lines, which significantly reduces USB noise. To add ESD protection they also added a static bleed resistor. Finally, like their previous receivers they continue to use a F-type RF connector and a TCXO for frequency stability.  

The price is $25.75 each plus flat rate global shipping of $4.50 and the receivers are expected to ship in mid-October. While we have not yet tested this model, it looks to be like a good receiver for those who need very low noise, or external power options.

They write:

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 selectability. 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.

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
– 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, 450mA) supply connector
– 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
– Circuit board can be mounted into a common 1455 case

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

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 450mA 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.

The ThumbNet N3
The ThumbNet N3
The ThumbNet N3 inside its optional 1455 aluminum enclosure.
The ThumbNet N3 inside its optional 1455 aluminum enclosure.

ThumbNet – A Low Cost Satellite Groundstation Network using modified RTL-SDRs

The ThumbNet project is a project that is aiming to provide low cost satellite receivers to students and any other interested communities in order to promote worldwide education in science, technology and engineering.

In addition to ThumbNet, there is also the ThumbSat project which hopes to launch it’s own satellites sometime next year. However, at the moment the focus is on ThumbNet where the team are currently building their ground station network by supplying customized RTL-SDR dongles to schools and interested communities all around the world for free.

Once the satellites are launched the receive stations will be used to download data from the ThumbSat satellites, creating a large network of receivers. To raise the incentive for participation, in the future they also hope to provide a small amount of money to each actively participating school or organisation. They write that the RTL-SDR’s could also be used for receiving other educational signals such as communications from the ISS. More information about the project can be found on their website www.thumbsat.com, and in this white paper (pdf).

As generic RTL-SDR dongles were not up to their specifications they decided to develop their own. Their RTL-SDR receivers are custom made to have a 1 PPM accuracy Temperature Controlled Oscillator (TCXO), a R820T2 tuner chip and a F-Type connector. The Type-F connector was chosen as they found that it was the most commonly found connector around the world and would be the easiest for students in remote areas to have access to.

If you are interested in getting one of these dongles and you meet their criteria (school or similar), you can either ask to participate in the ThumbNet program for free, or alternatively if you just want a dongle for your own use you can buy one through us. We have decided to help with the ThumbSat project by helping them advertise and sell off some of their surplus units through our blog.

In their official blurb ThumbSat writes:

Scoutek LTD, in the United Kingdom and ThumbSat Inc, in the United States are proud to have partnered together to provide an opportunity for schools and educational groups around the globe to promote radio science, technology, engineering and mathematics to their students and attempt to influence the next generation of scientists and engineers.  By donating small radio kits to each school or educational group, the project has already begun making a positive change in the lives of hundreds of students.

ThumbSat has been working with schools and educational groups around the globe and to date, more than 20 groups have committed to volunteering where students and staff members will operate the satellite monitoring stations as part of their science courses!  As a few examples, stations are being operated in diverse areas the Cook Islands, Christmas Island, Singapore, Ecuador, Tanzania and Botswana. One individual in Micronesia was operating the station by himself at 12 years old!

ThumbNet is open to anyone who is interested in participating and has a desire to setup and operate a small ground based radio listening station. No permits or licenses are required, since there is no transmission of any sort and no permanently installed antenna systems.

ThumbSat and Scoutek encourage education for everyone and is looking for anyone young, old, educated or uneducated, individuals or groups to participate.

Questions can be directed to [email protected], or by visiting the company websites: www.thumbsat.com or www.scoutek.com .

ThumbNet SDR Dongles
ThumbNet SDR Dongles with Wade, one of the people behind the project.