By Bob and Jann Koepke

When we think of ground stations for satellites, large antenna arrays and dishes immediately come to mind, along with a lot of expensive electronics.  But you can receive transmissions from many satellites using very inexpensive equipment.  An inexpensive RTL-SDR (Software Defined Radio) USB dongle and an omnidirectional antenna is a good start.

This simple ground station consists of just a few  components:

• A receiver – we’ll use a $20 USB Dongle Software Defined Radio (SDR).
• A Low Noise Amplifier (or LNA) is an optional component that can improve performance
• An antenna – we have used omnidirectional whips, discones, quadrafilar helix antennas, and directional yagis
• SDR software – we use SDR Console V2, which is free for non-commercial use
• Satellite tracking software or website – we use the N2YO website
• Websites to find the frequencies used by satellites – we use Amsat, PE0SAT, Zarya, and JE9PEL
• Data decoding software – we use WxtoImg for the NOAA weather satellites and the Funcube console for the Funcube CubeSat.
• A Personal Computer – laptop or desktop. Having more than one display helps
• Cabling to tie all of this together

Using these components and software, you should be able to hear transmissions from several different satellites.  To decode the data will take a slightly better antenna than the collapsible whip that comes with most of the RTL-SDR dongles (Quadrifilar Helix, Turnstile, Yagis).

Most of the frequencies of interest are below 500 MHz.  Weather satellites are around 137MHz,  many CubeSats use frequencies in the Amateur Radio 2 meter band(144 – 148 MHz) and 70cm band ( 420 – 450 MHz), and the ISS transmits data on the 2 meter ham band.  One of the largest challenges is determining which satellites are still functioning, especially with the CubeSats with their relatively short lives.

USB Dongle Software Defined Radio

A  Software Defined Radio is a “radio communications system where components that have typically been implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system (see Wikipedia, Article on Software Defined Radio: http://en.wikipedia.org/wiki/Software-defined_radio).  This can dramatically lower the cost of the radio for a simple system.

Inexpensive software defined radios have only recently become available with the introduction of the Realtek RTL2832U in 2010[1].  Very informative websites exist on just the RTL-SDR with source links and tutorials.[2]  And several books have been written on this subject[3].  Most of these will tune from about 30MHz to 1.7GHz; some go much further.  You can purchase up converters and down converters to extend the range.  More sophisticated SDRs can run several thousand dollars.  Although any will do, NooElec is one company that offers customer support and still has a reasonably priced radio at about $24.00[4] (photo is also from Amazon).

[1] Osmocom web site on RTL-SDR: http://sdr.osmocom.org/trac/wiki/rtl-sdr

[2] RTL-SDR web site:  http://www.rtl-sdr.com/

[3] The Hobbyists Guide to RTL-SDR:  http://www.amazon.com/Hobbyists-Guide-RTL-SDR-Software-Defined-ebook/dp/B00KCDF1QI

[4] NooElec USB Dongle SDR: http://www.amazon.com/NESDR-Mini-Compatible-Packages-Guaranteed/dp/B00P2UOU72/ref=sr_1_1

Low Noise Amplifier

The Low Noise Amplifier is optional.  The RF front end of the RTL-SDR radios is not the greatest (to some extent, you do get what you pay for).  The LNA4ALL covers 28MHz to 2.5GHz providing a gain of over 20dB in the frequency range of most of the satellites we will be receiving ( LNA4ALL web site:  http://lna4all.blogspot.com/, photo is also from this web site).  The LNA is particularly useful for amplifying the signals you are interested in while keeping  noise down.  And it is very useful to overcome coaxial cable loss if the antenna and receiver are located at some distance from each other.  LNA 4 all is available for 20Euros without the case and 80 Euros with the case (at the time of this writing, that is about $23 and $91, respectively, plus 5Euro shipping ($6).

The Antenna

Most of the RTL-SDR radios will come with a collapsible antenna.  This is sufficient to get started and verify that your radio is working.  But as you try to tune in satellites, you will need a better antenna, especially as you receive data from the NOAA weather satellites and CubeSats.  We built the Quadrifilar antenna and have been quite pleased with the performance.  The Omnidirectional antennas are easiest to begin with, since you do not need to worry about pointing the antenna at the satellite while receiving.   You will need to build an antenna for the frequency you wish to receive the satellite on, which is around 137 MHz for NOAA satellites, and 2m (144 MHz) and 70cm (430 MHz) for many amateur CubeSats.

The Quadrifilar Helix (QFH) Antenna is an excellent omni-directional antenna that can be built relatively easily for any of the frequencies of interest.  This image is taken from http://homepage.ntlworld.com/phqfh1/qfh_diy_guide.htm.  We have listened to NOAA weather satellites, several CubeSats, and the ISS successfully using this antenna.

The Turnstile antenna is another excellent and slightly easier to build omnidirectional antenna for the frequencies for many of the weather and CubeSats.  This image is taken from http://www.kr1st.com/na1ss.htm.   We have not tried this antenna, but will.

The Lindenblad antenna is described by Amsat as the Ultimate Satellite Omnidirectional Antenna.  It is constructed from four ½ wave diplose slanted 30 degrees to the horizon, placed 0.3 wavelength apart.  The photo is from an article taken from http://www.amsat.org/amsat/articles/w6shp/lindy.html.   We have not tried this antenna, but will.

In part two, we will talk about the software and give more details about antennas.