Category Archives: SatNOGS

Building a SatNOGS groundstation: Grounding and lightning protection

Dealing with grounding and lightning protection is obligatory when setting up a roof antenna. Bad grounding might cause not only damage to your antenna and equipment but even your complete home electronics or ignite fire.

Lightning is dangerous for two reasons. Direct lightning conduction can cause impulse voltages of higher than 20 Megavolts, whileas induced voltages can also reach up to 10 Kilovolts. Very interesting I found also this quote [1]:

A lightning has  an impulse voltage of > 20 Megavolts and an impulse current above 100.00 Ampere. Multiplying both numbers, the resulting yields a power that would instantaneosly vaporize any conductor. It does not, because the condctor does not actually conduct the energy of the lightning. The a cable with a diameter of 10mm alumium or 8mm copper only lays out a path, through which the surrounding air gets ionized, through which the actual charge surge current flows. This ionized stream will has a diameter of 2-5 cm and will not ignite anything, as the grounding conductor has a resistance <3 ohms.

Continue reading Building a SatNOGS groundstation: Grounding and lightning protection

Building a SatNOGS groundstation: Buying components I (electronics)

This page is a work in progress and will be updated on the way.

Last update: 2015-03-04

Overview of SatNOGS electrical components (1)
Part Comment Cost Am Source
Realtek RTL2832U Radio receiver 12-23 € 1 Amazon(DE)
Ebay
NooElec(US)
LM2596 Board Voltage regulator 2-6 € 1 Ebay(HK)
Arduino Micro Pro Microcontroller 12-20€ 1 Amazon(DE)
Sparkfun(US)
TP-Link WR703N Router 25€ 1  Ebay
Pololu A49888 Stepper motor driver 5€ 2 Pololu(US)
Ebay
NEMA 17 Stepper motor 15€ 2 Pololu(US) 
Ebay
Stepperonline
Sum 91-114€

Overview of SatNOGS electrical components (2)
Part Comment Cost Am Source
Connector
TCST2013 Optical Sensor
Resistors
http://www.reichelt.de/CNY-37/3/index.html?&ACTION=3&LA=446&ARTICLE=6682&artnr=CNY+37&SEARCH=gabellichtschranke
Sum 91-114€

The prices included are the prices I found for which you can buy these components new. Many of those parts are well known in the hacking world and you often find them overpriced, therefore you can take these prices as an orientation.

RTLSdr (RTL2832)

The software defined radio USB stick is basically just a hacked DVB stick. You can find those at cheap prices starting from 12 €uro everywhere. However, since this products is not intended for this purpose, some improvements can be made to the design, for instance a better crystal oscillator for better frequency stability or diodes for a smoother supply voltage. This improvements can have effect on your temperature stability and frequency offset. However those are not critical, but a nice feature to have for just a couple Euro more.

Further, the receiver comes with a variety of different (supported) tuners (E4000, R820T, R820T2 among those as the ones which are most commonly around).

The E4000 was the original tuner which is said to have better performance than the later R820T. However ever since the E4000 is now hardly available and prices have skyrocketed. Between the R820T and R820T2 a comparison shows a marginally better background noise and sensitivity is achieved by the R820T2.

LM2596 Voltage regulator

The LM2596 is a very small, however very powerful and efficient switching step-down voltage regulator. It creates a lower output voltage (as for instance 5V) from a higher supply voltage. They can supply up to 2-3 amps which is sufficient for most projects and have a very small footprint. To avoid designing the whole converter including inductors, capacitors etc. you can buy simple breakout boards for just several €uro. However be aware that there exist plenty different breakout boards of different sizes. Use the ones which have dimensions of about 41mmx21mm, e.g. the common small footprint without a voltage display.

The breakout boards you commonly find only have an 33μH as you can see on the pictures (inductor marking 330). According to the datasheet the inductance for 12V->5V would be best to have a higher inductance (68 μH), but for the currents required, less than 1 Ampere@5 Volts, is still highly sufficient. The 5 Volt line has to supply has to power the RTLSDR takes about ~300mAWR703N router about ~100mA, the Arduino usually at less than ~25mA.

TP-LINK WR703N

Although you could use any (old) router that supports the open-source firmware OpenWRT that has USB, the WR703N advantages are its very small size (57x57x18mm³), very low power consumption and price, and that it is well known to the OpenWRT community (which is worth a lot). Disadvantages generally speaking are the fact that it has no external Wifi antenna and in the lower range of ram and flash memory. (Although there are documented hacks to increase both). If you are willing to invest some Euro more you can probably go for other supported routers (e.g. tl-wr1043nd) but then you can quickly run into space problems inside the tracking box.

Be sure not to buy the WR702N, although very similar it has to few memory to run the linux distribution and is therefore absolutely unusable for this purpose.

You can get this one for instance on Ebay or Amazon for less than 25€.

Building a SatNOGS groundstation: Introduction

The project uses many well established hacks and combines them in a very clever way,  without needing to re-invent the wheel.
Software Defined Radio for instance using an inexpensive DVB-T receiver hack allows to receive radio communications with a very wide bandwidth for just around 20$.
The usage of a small router TL-WR703N, which has been also whichs hardware has been well explored by the open-source community running an very customizable open-source firmware, OpenWRT, which has been around for a long time already and can be used easily on productive.

3D printing has been around for several decades and hit consumer market just a couple of years ago. There are plenty of software and hardware tools available for little money, or even suppliers on the internet, that allow cheap manufacturing of prototype parts.

SatNOGS team currently is a group of people based in a hackerspace in Athen, Greece.

You can find an illustrated assembly instruction for the mechanical parts and electronical parts here: http://satnogs.dozuki.com/Guide.

Website: https://satnogs.org/

(c) SatNOGS
(c) SatNOGS