Building A Simple and Inexpensive CubeSat Satellite Ground Station – Part 2
By Bob and Jann Koepke
- In part 1, Bob and Jann wrote about the USB SDR (Software Defined Radio), the LNA (Low Noise Amplifier), and various sateliite antennas. Now in part 2 (the final part), they describe the software, the QFH (Quadrafilar Helix antenna) they built, and how to put everything together.
With the Software Defined Radios, part of the radio is in the “radio” (or USB dongle), and the rest is in software running on your personal computer. There are several different software packages available; most you can download for free. These allow changing the receive frequency of the radio, you can change the modulation type, and many allow you to decode digital data or even help track satellites and handle the Doppler shift. Most also have a waterfall display – so you can see a piece of the RF spectrum around the signal you are listening to. Many modulations and data types have a unique look on the waterfall display; this helps not only identify the frequency, but what is being transmitted.
The SDR Console V2 software is available at http://v2.sdr-radio.com and is our favorite SDR radio software. You can store multiple favorite frequencies and it has multipleVFOs for tuning. The satellite tracking window will help identify satellites in range, and display altitude, azimuth, and distance during the pass. You can also set it up to help with the Doppler shift..
SDR Sharp is another very popular radio software, with many plug-ins available. It is not quite as feature rich as SDR Console, but still a very useful tool. You can find SDR Sharp at http://sdrsharp.com/#download..
Installing the software Defined radio and Drivers
In addition to the SDR software, you will need a program called Zadig. It comes along with SDR Sharp (or you can download if from the Zadig web site: http://zadig.akeo.ie).
- Download the SDR Sharp radio software: http://sdrsharp.com/#download
- Follow the instructions on http://www.rtl-sdr.com/rtl-sdr-quick-start-guide to install SDR Sharp as well as the drivers
Satellite Tracking Software
You need to know when the satellite will be in range of your ground station. There are web sites that can provide this information as well as programs that will not only tell you when the satellite is in range, but also help you track it (some of the SDR radio software programs also perform this function).
N2YO.COM will allow you to pick the satellite to track, list the passes where the satellite will be in range over the next few days, and provide real time location data. The web site is http://www.n2yo.com. Click on “Satellite on orbit” to select the satellite you are interested in. You will need to enter your latitude and longitude for accurate information, or it will estimate your location from your IP address. Heavens above is another site often used (http://www.heavens-above.com).
SATPC 32 is a stand-alone software program that will also help track satellites. It is available for free, but you need to enter your location each time you start it. Or you can purchase a copy that helps fund Amsat.org. See http://store.amsat.org/catalog/product_info.php?products_id=50. You can also save a few dollars by joining Amsat at the same time that your order the product.
Once you have identified the Satellite that you want to track and when it will be in range, you will need to determine the frequencies that the satellite transmits on and what is being transmitted. There are good lists of frequencies at http://www.ne.jp/asahi/hamradio/je9pel/satslist.htm. The Zarya.info web site also lists satellite frequencies at http://www.zarya.info/Frequencies/FrequenciesAll.php. It also helps to Google the satellite name (many of the CubeSats and Amateur satellites have several names). We have had good luck with listings from Amsat (http://www.amsat.org) and PE0SAT (http://www.pe0sat.vgnet.nl).
The software that you will need to decode signals you get from Satellites depends upon the data that you are expecting. A few of the easier satellites to receive and decode are the NOAA weather satellites NOAA-15, NOAA-18, and NOAA-19. These satellites transmit pictures of the earth with cloud cover and IR data. The WxtoImg software at http://www.wxtoimg.com will decode the NOAA weather satellite images. It is free; there is also a paid-for version. We received the image shown to the left using the equipment in this article.
The Funcube web site has a console to decode the Funcube and Ukube transmissions at http://funcube.org.uk/working-documents/funcube-telemetry-dashboard.
Putting it all together
We found it very convenient to use a roof-mount TV tripod with a 6 foot mast sitting in our yard. The mast has the antenna, Low Noise Amplifier, and Radio with very short coax lengths. We mounted the radio and LNA on a section of PVC pipe that we could slide over the mast to make it easy to take back inside out of the weather, and to modify as we tried various combinations. We then ran a long (three 5 meter) active USB cable back to our PC in the house. To power the LNA, we have a regulated 9VDC wall power supply in the house with two 25 foot cables to carry the power out the LNA on the mast.
You will need to purchase:
- An RTL-SDR such as this one from Amazon: http://www.amazon.com/gp/product/B00P2UOU72
- An aluminum enclosure is optional: http://www.amazon.com/Extruded-Aluminum-Enclosure-Select-RTL-SDRs/dp/B00NZ2I6QA
- An ACTIVE USB 2.0 extension cable from Amazon (don’t get a USB 3.0 active cable as 3.0 is much noisier) – there are many brands, this one from Tripp Lite is available in 5, 10, and 20m length: http://www.amazon.com/Tripp-Lite-U026-016-Extension-Repeater/dp/B0002D6QJO
If you DON’t use the LNA:
- If you don’t use the LNA you’ll need a MCX to UHF SO 239 PL-259 female cable (or MCX to whatever connector you use on your antenna): http://www.amazon.com/gp/product/B00C20FV78
If you DO use the LNA add (it is a lot to add, but well worth it):
- The Low Noise Amplifier is optional – if you choose to use it: http://lna4all.blogspot.com
- An MCX to SMA cable from the radio to the preamp: http://www.amazon.com/gp/product/B00ISTDOOO
- A cable from the LNA to the antenna – we used PL-259 on the antenna (SMA to UHF SO239 PL-259): http://www.amazon.com/gp/product/B004280GQ4
- You will also need a 9VDC regulated power supply (LNA for all takes 6VDC to 12VDC in – be careful of the inexpensive non-regulated “wall-wart” power supplies as even a 9VDC unregulated supply can be more the 13VDC under light loads): https://www.sparkfun.com/products/298. A similar one is available from Amazon at: http://www.amazon.com/650mA-Wall-Adapter-Power-Supply/dp/B007R9TJTU (I believe it is the same, but did not order the Amazon power supply)
- A short power cable with 2.1mm x 5.5mm connector. Cut the cable and connect a short cable with the female connector to the LNA: http://www.amazon.com/2-1mm-5-5mm-Extension-Cable-Adapter/dp/B00FTH6WNS
- One or more extension cable for LNA power (25ft with 2.1mm x 5.5mm connectors): http://www.amazon.com/2-1mm-5-5mm-Extension-Cable-Adapter/dp/B00FTGAJW4
Operating the software Defined radio
You can start SDR Sharp with your dongle plugged in and the telescoping antenna on your desk and verify you can tune to an FM station like K-EARTH at 101.1MHz. The RTL-SDR radio does not tune below 27MHZ, so don’t try to tune to AM stations or listen to “short wave radio” – the dongle does not cover those frequencies even though you can tune to them. If you move your PC and antenna outside, or move the antenna and dongle outside and connect to your PC inside with an active USB cable, you can tune around and find many more stations to listen to. Your PC generates a lot of RF noise, so getting the RTL-SDR dongle away from the PC helps. You can also use the metal case around the dongle to lower some noise. USB 3.0 is much noisier than USB 2.0 so it helps us use USB2.0 from your PC. You may need a ferrite bead on the USB cable as well. Some easy-to-hear frequencies are
- FM Broadcast from 88 – 108 MHz
- Aviation frequencies from 118 to 136 MHz
- NOAA weather reports: http://www.nws.noaa.gov/nwr/coverage/stations.php?State=CA. Knowing these frequencies is also a good method to calibrate your radio frequency.
- Santa Ana on 162.45 MHz is easy to hear
- Los Angeles on 162.55 MHz is easy to hear
- 2M Amateur Radio Band: 144 to 148 MHz
- The K6JSI repeater on 147.210 is easy to hear, and very active. It is on the WINsystem that ties many repeaters together, so you will hear stations from many states through the local repeater: http://www.winsystem.org/index.html
We prefer and use the SDR Console software available at: http://v2.sdr-radio.com/Download.aspx. SDR console has several VFOs as well as satellite tracking support and some data decoding built in. It is much more feature rich than the SDR Sharp program, although SDR Sharp has plug-ins for a variety of functions as well. You will still need to install the drivers via Zadig – once you followed the instructions under SDR Sharp you have the drivers installed for SDR Console as well. The quick start guide for SDR Console is here: http://v2.sdr-radio.com/Support/QuickStart.aspx. There is additional information for the RTL-SDR radios here: http://v2.sdr-radio.com/Support/RTLSDRs.aspx. If the RTL-SDR USB options does not appear, you can download the support package .zip here: http://m3ghe.blogspot.com/p/adding-support-for-rtl-sdr-usb-dongles.html
Moving the radio outside for better reception
To receive satellites you need an outdoor antenna. Traditional radio installations use an outdoor antenna and a long coaxial cable to a radio inside. The problem is that the coaxial cable adds a lot of loss. You can overcome this by putting the radio near the antenna and connecting the radio to the PC inside using an active USB cable. We found that the LNA improved reception substantially with the inexpensive RTL-SDR dongles. We did not weatherproof the radio and LNA; we also made it very simple to install and remove electronisc by using Velcro straps to secure everything to a piece of PVC pipe that we can easily slide on and off our 6 foot mast on tripod – all on our lawn – then bring it back inside:
The outside antenna assembly consists of four separate parts:
- The tripod – really meant for mounting a TV antenna on a roof
- A 6 foot or so mast
- A 2 foot long PVC pipe with radio and LNA that slides over the mast
- The antenna; the bottom slides over the top of the mast.
We have had excellent results with a Right Hand Circularly Polarized Quadrifilar Helix antenna. We used the plans from: http://homepage.ntlworld.com/phqfh1/qfh_diy_guide.htm. It is made of ½” copper pipe (about $8 for a 10 foot section at Home Depot, and some 90 degree elbows. We added the PVC support in the center
LNA with Radio, cables, and LNA power supply mounted on the 2 foot long PVC pipe
Top of PVC with LNA and Radio coax at top goes to the antenna
Center of PVC with LNA and Radio connected by a short piece of coax
Bottom of PVC with LNA and Radio – active USB cable goes to PC and cable with barrel connectors goes to 9VDC
The Quadrifilar Helix (QFH) Antenna
You will need to build (or purchase) an antenna – we chose the Right Hand Circularly Polarized Quadrifilar Helix antenna. We have built one for 137MHz and it works OK for receiving not only the NOAA weather satellites, but also the satellite transmissions on the 2M amateur band. It would be best, of course, to build one for each range of frequencies of interest. We made this design out of ½” copper pipe since it appeared to be quite sturdy and would not be deformed when moving it around. Virtually everything is available at home depot. The pipe is quite easy to bend, but if you are not careful it kinks easily. We filled it with water, then froze it. While the water was still ice, we slowly bent it using a conduit bender – it takes patience.
- You can purchase a QFH antenna here: http://www.nationalrf.com/satellite-tenna.htm
- Instructions to make the antenna can be found in links on this home page: http://homepage.ntlworld.com/phqfh1/qfh_diy_guide.htm
- The antenna instruction .PDF is here: http://homepage.ntlworld.com/phqfh1/qfh.pdf
- The balun instruction .pdf is here: http://homepage.ntlworld.com/phqfh1/phbalun1.pdf
Easy Satellites to start
It is helpful to have several screens running simultaneously on your PC – three would be ideal, two is OK.
- One screen would be for the SDR console radio software, such as SDR Console V2
- One screen would be for tracking, such SDR Console V2 tracking screen, or N2YO
- One screen would be for the decoding software
One of the easiest satellites to hear is the NOAA weather image satellites. The NOAA satellites are well powered and easy to hear – they have a distinctive tick-tock sound and look unique on the SDR console. Use the PCs internal mixer to route the audio from the SDR radio software to WxtoImg, or use an external cable. The volume needs to be relatively high. You do not need to worry about Doppler shift as you can set the bandwidth of the radio wide enough to track OK.
|Satellite Name||NORAD ID||Frequency||Modulation & BW||Decoding S/W|
|NOAA-15||25338||137.620 MHz||FM Data Wide
|NOAA-18||28654||137.9152 MHz||FM Data Wide
|NOAA-19||33591||137.100 MHz||FM Data Wide
The Funcube satellite is also relatively easy to hear – and it has a distinctive look on the SDR radio software as well as sound. Like many of the CubeSats, it has several names (Funcube-1, AO-73). Funcube-2 is also known as Ukube-1. Sometimes the only way you know for sure you are looking up tracking information for the correct satellite is through the NORAD ID.
|Satellite Name||NORAD ID||Frequency||Modulation & BW||Decoding S/W|
|Funcube-1 (AO-73)||39444||145.935 MHz||USB Data (24KHz)||Funcube Telemetry Dashboard|
|UKUBE-1 (Funcube-2)||40074||145.915 MHz||Funcube Telemetry Dashboard|
Happy satellite hunting!