Raspberry Pi Satellite Tracker Interface How To

GHTracker Running On A Raspberry Pi 3

Sat Tracker – GH Tracker Running On A Raspberry Pi 3 B+

I have received several requests to share the image and construction details for the Raspberry Pi Satellite Tracker Interface that we use with MacDoppler as part of the Satellite Stations here. You can read more about the motivation for this project and its initial design and testing here.

This article explains how to put a Sat Tracker together.

The information and software described here are provided on an “as is” basis without support, warranty, or any assumption of liability related to assembly or use. You may use information and software image here only at your own risk and doing so releases the author and Green Heron Engineering from any liability for damages either direct or indirect which might occur in connection with using this material. No warranty or liability either explicit or implicit is provided by either AB1OC or Green Heron Engineering.

Now that we have that out-of-the-way, here are the components that you need to build your own Sat Tracker:

The Sat Tracker image includes a display driver for the specific touch display listed above and will most likely NOT WORK with any other touch display. You will also need a Green Heron RT-21 Az/El or a pair of Green Heron RT-21 single rotator controllers from Green Heron Engineering that are properly configured for your rotators.

If you have not worked with the Raspberry Pi before, it’s a good idea to begin by installing NOOBS on your SD card and getting your Raspberry Pi to boot with a USB Keyboard, USB Mouse, and an HDMI display attached. This will give you a chance to get familiar with formatting and loading your SD card with the Raspbian build of the Debian OS for the Raspberry Pi. I’d encourage you to boot up the OS and play with it some to get familiar with the OS environment before building your Sat Tracker.

Etcher Writing Raspberry Pi SD Card Image

Etcher Writing Raspberry Pi SD Card Image

The first step in building your Sat Tracker is to put together the hardware and write the image to your SD Card. Use the enclosed instructions or search the web to find information on how to do each of these steps:

  1. Install the Heat Sinks on the Raspberry Pi 3 B+ Motherboard. Make sure your chipset heat sink will clear the back of the case. If it won’t, it’s fine to just install the CPU Heatsink.
  2. Assemble your case to the point where it is built up to support the touch display
  3. Carefully install your touch display on the Raspberry Pi Motherboard
  4. Install the remaining pieces of your case including the nylon screws and nuts which hold the case parts together
  5. Download the SD Card image from the link below, unzip it, and load the image onto your SD card using Etcher
  6. Install your SD card in the slot on your Raspberry Pi Motherboard
  7. Connect your Raspberry Pi to the outside world as follows:
    • Connect Two USB cables – one end to the Elevation and Azimuth ports on your Green Heron Engineering RT-21 Controller(s) and the other ends to two of the USB connections on the Raspberry Pi
    • Connect a wired Ethernet Cable to your Raspberry Pi via a common Ethernet Hub or Switch with a PC or Mac that has VNC Viewer Installed. You will need a DHCP server running on the same network to supply your Raspberry Pi with an IP address when it boots. Your router most likely provides a DHCP function.
    • Connect your USB power supply to the Raspberry Pi Motherboard and power it up

Your Sat Tracker should boot up to the desktop with GH Tracker V1.24 running. The touch display works fine for using GH Tracker but its a bit small for configuring things. To make the configuration steps easier, the image comes up running VNC Server. I like to use VNC Viewer on my PC to connect to the Sat Tracker using VNC to perform the steps that follow. Note that both the Raspberry Pi and your PC must be on the same sub-network for the VNC connection to work. I’ve also included the following commands in the Sat Tracker image which can be run from the Raspberry Pi terminal window to make the configuration process easier:

$ setdisp hdmi # Disables the TFT display & uses the HDMI interface
$ setdisp tft  # Disables the HDMI interface & uses the TFT display
$ reboot       # Reboots the Raspberry Pi causing
               # the latest display command to take effect

If you select the HDMI interface, you will find that VNC Viewer produces a larger window enabling you to perform the following configuration steps:

  1. First, you need to determine the IP address of your Sat Tracker. This can be done via your DHCP server or by touching the network icon (up and down arrows) at the top of the display on the Sat Tracker.
  2. Use VNC Viewer on your PC or Mac to connect to the IP address of your Raspberry Pi. The default password is “raspberry“.
  3. Once you are connected, open a terminal dialog on the Sat Tracker, set your display to hdmi mode via the command shown above, and reboot your Sat Tracker.
  4. Reconnect VNC Viewer to your Sat Tracker and click on the Raspberry button (Start Menu Button) at the top left of the screen, select Preferences, and run Raspberry Pi Configuration. Select Expand Filesystem from the System Tab. This will expand the filesystem to use all of the available space on your SD Card. You can also change the system name of your Sat Tracker and your login password if you wish. When you are done making these changes, reboot your Sat Tracker.
  5. Reconnect to your Sat Tracker via VNC Viewer and select Setup -> Rotator Configuration from the menu in the GH Tracker App. Select the TTY devices (i.e. COM Ports) associated with the Azimuth and Elevation connections to your RT-21 Controller(s) via the two dropdown boxes. You can also configure the operational parameters for GH Tracker at this time. The ones that I use with our Alfa-Spid Az/El Rotators are shown below.

    GH Tracker Rotator Configuration

    GH Tracker Rotator Configuration

  6. Configure your Green Heron Engineering RT-21 Controllers to work with your rotator(s). The settings below are the ones that we use with the RT-21 Az/El controller and Alfa-Spid Az/El Rotators that we have here.

    GHE RT-21 Az/El Controller Settings for Alfa-Spid Rotator

    SettingAzimuthElevationNotes
    Park Heading0 degrees90 degreesSet via MacDoppler. Minimize wind loading and coupling to antennas below. Also enables water drainage from cross-boom tubes.
    Offset180 degrees0 degreesAzimuth dead spot is South. Elevation headings are from 0 to 180 degrees.
    Delays6 sec6 secMinimize relay operation during computer tracking
    Min Speed23Creates smooth start and stop for large array
    Max Speed1010Makes large movements relatively quick
    CCW Limit180 degrees355 degreesCCW and CW limits ensures predictable Azimuth heading for range around 180 degrees. Elevation limits permit 0 to 180 degree operation. Elevation limits shown can only be set via GHE configuration app.
    CW Limit179 degrees180 degrees
    OptionSPIDSPIDAlfa-Spid Az/El Rotator
    Divide Hi360360Rotator has 1 degree pointing accuracy
    Divide Lo360360
    Knob Time4040Default setting
    ModeNORMALNORMALDefault setting
    Ramp66Creates smooth start and stop for large array
    Bright22Easy to read in shack
  7. Configure the source of tracking data to be MacDoppler (UDP) from the GH Tracker Source Menu. We use UDP Broadcasts with MacDoppler running on the same Mac with VNC Viewer to run our rotator. Finally, press the Press to start tracking button on GH Tracker and run MacDoppler with UDP Broadcast on and Rotators Enabled to start tracking.

    MacDoppler Tracking AO-91

    MacDoppler Tracking AO-91

  8. Once you are satisfied with the operation of your Sat Tracker, use VNC Viewer to access the terminal window on your Sat Tracker one last time, set your display to TFT, and reboot.

The most common problems that you’ll run into are communications between your Sat Tracker and your Green Heron Engineering RT-21 Controller(s). If the Azimuth and Elevation numbers are reversed in GH Tracker, simply switch the TTY devices via the Setup Menu in GH Tracker. Also, note that it’s important to have your RT-21 Controller(s) on and full initialized BEFORE booting up your Sat Tracker.

Most communications problems can be resolved by initializing your tracking system via the following steps in order:

  1. Start with your RT-21 Controller(s) and you Sat Tracker powered down. Also, shutdown MacDoppler on your Mac.
  2. Power up your RT-21 Controller(s) and let the initializations fully complete.
  3. Power up your Sat Tracker and let it fully come up before enabling tracking in GH Tracker.
  4. Finally, startup MacDoppler, make sure it is configured to use UDP Broadcasts for Rotator Control and make sure that Rotators Enabled is checked.

The VNC Server on the Sat Tracker will sometimes fail to initialize on boot. If this happens, just reboot your Sat Tracker and the VNC Server should initialize and enable VNC access.

I hope you have fun building and using your own Sat Tracker.

Fred, AB1OC

Update on NARS Amateur Radio Expo for Young People

Source: Update on NARS Amateur Radio Expo for Young People

The Nashua Area Radio Society will again be hosting an Amateur Radio Exposition for Young People as part of NEAR-Fest in Deerfield, NH on October 12th and 13th.

You can see more about what we are planning via the link above. Activities will include multiple GOTA Stations, a Kit Build, a Fox Hunt, Morse Code, and other hands-on activities. We will also be operating a Special Event Station as N1T.

NEAR-Fest along with several NARS members are also sponsoring a matching fundraising project as part of this event. Check it out!

Fred, AB1OC

Please Help Us Grow the Amateur Radio Service

Graduates from our Summer Youth Technician License Class

Source: Support the Nashua Area Radio Society on Amazon Smile and GoFundMe

Anita and I have been working to grow the Amateur Radio Service through our work at the Nashua Area Radio Society. The Nashua Area Radio Society is a 501c(3) public charity whose mission is to:

  • Encourage and help people to become licensed and active in the Amateur Radio Service
  • Spark Interest among Young People in STEM Education and Careers through Ham Radio
  • Provide training and mentoring to enable our members to improve their technical and operating skills and to be prepared to assist in times of emergency
  • Sponsor on-air operating activities so that our members may practice and fully develop their operating skills and have fun with Ham Radio!
Students and Teacher Ready To Launch Their High-Altitude Balloon

Students and Teachers Ready To Launch Their High-Altitude Balloon

The Nashua Area Radio Society has created many programs designed to provide STEM learning experiences and training through Amateur Radio. Some of these include:

To carry out our mission, we have formed close relationships with several schools. This helps us develop and deliver effective, high-quality programs that bring learning through Amateur Radio to young people. You can read more about what we’re doing via the link at the top of the page.

We provide many of these services either free of charge or at a very modest cost. We count on the generosity of our members, friends, and the Amateur Radio community to raise funds to support our work.

We hope that our readers will consider supporting our work at the Nashua Area Radio Society by using Amazon Smile and designating us as your favorite charity and/or by making a donation to our current fundraising campaign (click on the badge below).

GoFundMe Badge

Amazon Smile is free and it’s easy to set up and use (click here for setup information).

On behalf of the many young people and others that we help, thank you very much for your interest and support. We will continue to work hard to provide learning opportunities for young people through Amateur Radio and to continue to make the Amateur Radio Service the best it can be to benefit everyone.

Fred, AB1OC

Fall Youth Events at Boxboro and NEAR-Fest

Quite a few Nashua Area Radio Society members have been working on a display to get young people and potential new Hams interested in Amateur Radio. Our display will be part of the New England Amateur Radio Convention in Boxboro, MA on September 8th and 9th. We are also planning a similar display for NEAR-Fest at Deerfield Fairgrounds, NH later in the fall. You can see more about our planned display and the associated hands-on activities via the following link.

Source: Fall Youth Events at Boxboro and NEAR-Fest – Nashua Area Radio Society

I want to share some information about an Amateur Radio event that we will be doing at the Boxboro, MA Ham Radio Convention in September. Our display and hands-on activities provide an introduction to Amateur Radio for young people and include information and a chance to try Amateur Radio activities such as:

You can read more about our plans for the event via the link above.

Morse Trainer Kit

Morse Trainer Kit

We’ve been working with Steve Elliot, K1EL to develop an inexpensive kit building project to include as part of our displays. We will be including a new kit building activity in as part of our display. Builders can purchase the Morse Trainer Kit shown above for $20 and build it at the show. We will provide soldering equipment and kit building mentors to help builders complete their kit. The package includes batteries and a printed manual. We will have these kits available for walk-up purchase at the show on both Saturday and Sunday.

I am also planning to provide forum presentation on the following topics on Saturday at Boxboro:

  • Creating Successful Youth Outreach Projects
  • Portable Satellite Station Design, Operation, and Planning for an upcoming ISS Crew Contact
  • STEM Learning for Young People via High Altitude Balloons Carrying Amateur Radio

You can view the Boxboro Forum schedule here.

I hope to see folks who follow our Blog at the New England at the Boxboro Convention. If you can make it, stop by our display or visit us in the forums and say “hello”.

73,

Fred, AB1OC

 

A Portable Satellite Station Part 6 – 3.0 Station Initial Contacts

Tech Class First 3.0 Portable Station Test

Tech Class First 3.0 Portable Station Test

With the construction of our Portable Satellite Station 3.0 complete, we’ve been looking forward to an opportunity to test the new setup. We chose the Nashua Area Radio Society’s recent Technician License Class as a good time to both test the new stations and to acquaint our Tech Class grads with one of the many things that they can do with their new licenses – amateur satellite operations.

Tech Class 3.0 Portable Satellite Antenna Test

Tech Class 3.0 Portable Satellite Antenna Test

The first transport of the new 3.0 station antenna system turned out to be simple. The booms and counterweights of the new antenna system are easily separated via the removal of a few bolts located at the cross-boom. This allowed the antennas feed-points, rotator loops and polarity switching connections to be removed and transported as complete assemblies. The separation of the longer-boom antennas into two sections also made transporting the antennas easier and made the antenna elements less prone to bending in transport. Setup and cabling of the new 3.0 antenna system as the class site was quick and simple.

The opportunities to make contacts during our Tech Class were limited but the new system performed well with one exception. We saw a higher than expected SWR readings on the 70cm yagi during transmit. We immediately suspected problems with one of the N connectors that were installed during the construction of the new system (component testing during assembly showed the SWR readings on the 70cm side of the system to be in spec.).

Portable Satellite Station 3.0 Antenna System

Portable Satellite Station 3.0 Antenna System

After the class, we set up the 3.0 system again at our QTH. Transport and re-assembly of the new system are somewhat easier and faster than our 2.0 portable station antenna setup is.

Satellite Antenna System 3.0 Connections

Satellite Antenna System 3.0 Connections

The 3.0 antenna system uses a similar connector bulkhead approach that we used previously. The rotator controls are handled via a single, 8-conductor cable and we have a new connection for the polarity switching controls on the 3.0 system yagis.

Rotator Loop Coax Retention System

Rotator Loop Coax Retention System

We have had some problems with the connections between the preamplifiers mounted at the antennas and the rotator loops which connect the antennas to them. This problem caused several failures in the associated N-connectors on the 2.0 portable antenna system so we fabricated a simple arrangement to prevent the rotation of the antennas from turning the coax inside the N-connectors and causing these failures.

70cm Yagi SWR in the Satellite Sub-Band

70cm Antenna and Feedline SWR in the Satellite Sub-Band

Some isolation tests were performed on each cabling element of the 70cm side of the 3.0 antenna system and this resulted in the location of an improperly installed N-connector. The faulty connector was easily replaced and this corrected the SWR readings on the 70cm side of the antenna system. The image above shows the SWR readings for the 70cm antenna after the faulty connector was replaced. We checked the SWR performance with the 70cm yagi set for both Left-Hand and Right-Hand Circular Polarization and we saw good results in both configurations.

2m Yagi SWR in the Satellite Sub-Band

2m Antenna and Feedline SWR in the Satellite Sub-Band

We also re-checked the SWR performance of the 2m side of the antenna system with the 2m yagi in both polarity settings and it looked good as well.

Portable Satellite Antenna 3.0 Az-El Rotator

Portable Satellite Antenna 3.0 Az-El Rotator

The 3.0 antenna system uses an Alfa-Spid rotator. The Alfa-Spid can handle the additional weight of the larger yagis and has a more precise pointing ability (1° accuracy) which is helpful given the tighter patterns of the larger, 3.0 yagis.

70cm Yagi Switchable Polarity Feedpoint

70cm Yagi Switchable Polarity Feedpoint

The new yagis in the 3.0 antenna system have feed point arrangements which allow the polarity of the yagis to be switched between Left-Hand Circular Polarity (LHCP) and Right-Hand Circular Polarity (RHCP). These antennas used a relay arrangement at the feed-points that flip the polarity of one plane of the yagis by 180° which in turn changes the polarity of the antennas between LHCP and RHCP.

Portable Satellite Station 3.0 Radio and Controls

Portable Satellite Station 3.0 Radio and Controls

With the SWR problem corrected, we set up the 3.0 station radio and controls. The 3.0 station adds our homebuilt PTT Router and the control box from DXengineering which controls polarity switching. Also, the Green Heron rotator control box has been configured to control the new Alfa-Spid rotator.

POrtable Satellite Station 3.0 Computer Control via MacDoppler

Portable Satellite Station 3.0 Computer Control via MacDoppler

We are continuing to use the excellent MacDoppler software to control the 3.0 station. MacDoppler provides tracking controls for the antennas and doppler correction for the Icom-9100 transceivers uplink and downlink VFOs.

Satellite 3.0 Station Control Details

Satellite 3.0 Station Control Details

The image above shows a closer view of the 3.0 station controls. The box in the middle-left with four LEDs and the knob is used to select one of four polarity configurations for the 2m and 70cm yagis – RHCP/RHCP, LHCP/RHCP, RHCP/LHCP, or LHCP/LHCP. Just to the right in the middle stack is our homebrewed PTT Router which expands and improves the PTT sequencing performance of the station. Our station also uses a WaveNode WN-2 for SWR and power monitoring.

So how does the new 3.0 station perform? The new antennas have a tighter pattern requiring careful pointing calibration of the rotators during setup. This is easy to do with the Alfa-Spid rotator. The new antennas have noticeable more gain as compared to the LEO pack used on the 2.0 station. We are also surprised to see how much difference the polarity switching capability makes in certain situations – sometimes as much as two S units (12 dB) in certain situations. The combination of the new antennas and selection of the best polarity combination allows solid operation on many satellites passes with as little as 2 watts of uplink power. We have made a little over 50 QSOs on the new 3.0 station so far and it works great! For more information on the Portable 3.0 Station as well as the 2.0 and 1.0 stations that we’ve built – see the links below:

Fred, AB1OC

 

PTT Router for Satellite Station 3.0

ARR Satellite Preamp

Advanced Receiver Research Remote Preamp

Our Satellite Station 2.0 antenna system uses a pair of Advanced Receiver Research Remote preamplifiers at the antennas to boost weak signals. These preamps have RF sensing and switching to protect them during transit. While this system works well; we are always concerned about the impact of the RF power affecting the long-term reliability of these devices and the associated radio equipment.

M2 Antenna Systems S3 Sequencers

M2 Antenna Systems S3 Sequencers

Our Satellite Station 2.0 uses a pair of M2 Antenna Systems S3 Sequencers to control the preamps remotely. For U/V and V/U mode satellites, it’s a simple matter to turn off the uplink band preamp to protect it against RF during transmit. The problem with this approach comes when working satellites and the International Space Station in simplex (single band) modes. In these situations, we need a solution which keys the sequencers externally so that the sequencers can properly control the changeover of the preamps from receive to transmit mode before keying our radio (an Icom IC-9100). We also wanted a solution which could also allow the radio initiate the keying of the sequencers for CW break-in keying and digital modes.

PTT Router

PTT Router

Our solution was to design and build a simple Push-To-Talk (PTT) router. This device allows an external source such as a footswitch or a trigger switch to initiate the keying. The design also includes indicators which confirm that the keying sequence has completed.

PTT Router Schematic Diagram

PTT Router Schematic Diagram

Our first step was to create a simple design which allowed for either an external switch or the radio to initiate keying. The PTT source switch (S1) selects the keying source and uses the Hsend  (2m key) and Vsend (70cm/1.2 GH key) lines on the Icom IC-9100 accessory jack as either the means to key the radio or the means to detect that the radio has initiated a transmit keying sequence. A second switch (S2) selects which VFO is keyed when the keying source switch (S1) is in External mode. Finally,  indicators for power and keying complete were added.

Rear Panel Connectors

Rear Panel Connectors

A small enclosure was used to house the switches, indicators, and the connections to the rest of our Satellite Station. The image above shows the rear-panel connections to external PTT sources, the S3 Sequencers, the IC-9100 Radio, and a 12 Vdc station power source.

PTT Router Internal View

PTT Router Internal View

A pair of terminal strips were mounted inside the enclosure to make connecting all of the components easier. The wiring is pretty dense around the front and rear panels so connections were insulated with heat shrink tubing. A small PCB could easily be created to make replicating the prototype easier should we decide to build more copies of the design.

Satellite Station 3.0 Controls

Satellite Station 3.0 Controls

Our new PTT router was easy to integrate into our Satellite Station 3.0 setup. Integration required some custom cables to be made to connect our PTT router to the sequencers and to the accessory jack of the radio. With the integration completed, we are now able to properly sequence the control of the preamps and the radio in all modes of operation. Here are some more articles which include more about our portable satellite stations –

Fred (AB1OC)

DX Alarm Clock Part 2 – Hardware

The DX Alarm Clock

The DX Alarm Clock

I recently wrote a blog article about the DX Alarm Clock software – here is Part 2 of the Series on the how I built the hardware for the DX Alarm Clock.

DX Alarm Clock Hardware Components

The DX Alarm Clock is based on a Raspberry Pi 3 computer and an Adafruit Pi-TFT Touch Screen Display.  The list of components, along with links is below.  Since I built the Raspberry Pi almost a year ago and technology is always advancing, some of the parts are no longer available or have better replacements available.  I’ll provide information on what I used and a recommended replacement.  Approximate prices are included.

 

Rapberry Pi 3

Rapberry Pi 3

 

Motherboard: Raspberry Pi 3 ($35) – includes a 1.2 GHz 64-bit quad-core ARM CPU, Build in WiFi, Ethernet, 4 USB Ports, an HDMI port and audio port (3.5″) and Bluetooth.

Also you will need a power adapter  ($10) and Class 10 Micro SD card ($15) for the Raspberry Pi.  Ours is a SanDisk Ultra 64GB Micro SD Card.

Pi-TFT Touch Screen Display

Pi-TFT Touch Screen Display

Display: Adafruit Pi-TFT 2.8″ Display with Capacitive Touch Screen ($45).  A slightly larger, 3.5″ display is now available.

PiBow Case

PiBow Case for Raspberry Pi and Touch Screen Display

Case: Pimoroni PiBow Case for Raspberry Pi and Pi-TFT Display($20)

Kinivo Speaker

Kinivo Portable Speaker

Portable Speaker:  Any small portable/rechargeable speaker will do.  Mine is a Kinivo, but it is no longer available.  Any small speaker will do as long as it is Bluetooth or has a 3.5″ stereo connector.

 

Raspberry Pi Development Environment

Raspberry Pi Development Environment

Raspberry Pi Development Environment

After constructing the Raspberry Pi, case and TFT Display, the next step was to connect it to a monitor via the HDMI port, a mouse via one of the USB ports and to a Bluetooth keyboard.   Then I loaded the Raspbian Operating System onto the Raspberry Pi via the micro SD card.  I first copied the OS to the Micro SD card using a PC or Mac and then inserted the card into the Raspberry Pi and booted from it.  You can find a good tutorial on how to do this at https://www.raspberrypi.org/learning/software-guide/quickstart/

Once Raspbian is installed, you will have a windows like GUI (Graphical User Interface) environment with a web browser, and a number of additional applications included.

This gave me a development environment that I could use to build and test the DX Alarm Clock software.  I used the Python language to develop the software.  I used the Python IDLE development environment, which is included in the Raspbian OS.

Interested in Raspberry Pi Amateur Radio Projects?  See the article on a Raspberry Pi Satellite Rotator Interface.

Raspberry Pi Satellite Rotator Interface

MacDoppler and GHTracker

MacDoppler and GHTracker

We’ve been using our Portable Satellite Station 2.0 for some time now and it works great. One area that can be improved is the interface between the MacDoppler Satellite Tracking program we use and the GHTracker application which controls the Green Heron Engineering RT-21 Az/El Rotator Controller in our setup. Our initial approach was to run the GHTracker app under Windows/VMWare on the same MacBook Air laptop that runs MacDoppler. While this approach works ok, it was more complex and less reliable than we had hoped.

Fortunately, the interface between MacDoppler and GHTracker uses a UDP-based interface which will run over an IP network.

GHTracker Running On A Raspberry Pi 3

GHTracker Running On A Raspberry Pi 3

Anita, AB1QB got great results using a Raspberry Pi 2 with a Touch Screen for her DX Alarm Clock Project so I decided to do something similar with GHTracker. The new Raspberry Pi 3 Model B boards feature a built-in WiFi networking interface and four USB ports which made the RPi 3 a perfect platform for this project. An email exchange with Jeff at Green Heron Engineering confirmed that GHTracker could be made to run under Linux on the Raspberry Pi (RPi).

We wanted a compact package that did not require anything but a power supply to run the final project. There are lots of great choices of parts to build a Raspberry Pi system. Here’s what we used:

Total cost for all of the parts was $120.

Assembly of the case and the hardware was straightforward. The folks at Adafruit provide a pre-built Jesse Linux image for the RPi which includes the necessary driver for the Touch Screen Display.

After a bit of configuration work and the creation of a few shell scripts to make it easy to boot the RPi to an HDMI display or to the Touch Display, we were ready to install the GH Tracker App. we also enabled the VNC Server on the RPi so that we could use a VNC Client application on our MacBook Air in place of directly connecting a display, keyboard, and mouse to the RPi. Finally, we installed Samba on our RPi to allow files to be moved between our other computers and the RPi.

GHTracker Running on the Raspberry Pi

GHTracker Running on the Raspberry Pi

Jeff at Green Heron Engineering provided a copy of GHTracker V1.24 and the necessary serial interface library to enable its use on the RPi. Jeff is planning to make a tar file available with GH Tracker and the library in the near future. We did some configuration work on LXDE (the GUI interface for Linux that runs on the RPi) automatically run GH Tracker whenever the RPi is booted up. We also optimized the GUI for the sole purpose of running GH Tracker on the Touch Screen Display. Finally, we configured the Ethernet and WiFi interfaces on the RPi to work with our home network and with our LTE Hotspot modem.

RPi GHTracker Test Setup

RPi GHTracker Test Setup

With all of the software work done, it was time to test the combination with our Satellite Rotator System. The setup worked on the first try using a WiFi network connection between the MacBook Air Laptop running MacDoppler and the RPi. The USB-based serial ports which control Azimuth and Elevation direction of the rotators worked as soon as they were plugged into the RPi. Also, the touchscreen interface works well with the GH Tracker App making the combination easy to use.

MacDoppler and GHTracker via VNC

MacDoppler and GHTracker via VNC

The VNC Client/Server combination allows us to work with the software on the RPi right form our MacBook Air laptop. It also makes for a nice display for monitoring the GHTracker App’s operation from the Mac.

You can find information about how to build your own Raspberry Pi Sat Tracker Interface here.

Other articles in the Portable Satellite Station series include:

You may also be interested in the satellite station at our home QTH. You can read more about that here.

Thanks to the help from Jeff at Green Heron Engineering, this project was very easy to do and worked out well. The Raspberry Pi 3 platform is very powerful and relatively easy to work with. It makes a great start for many Ham Radio projects. Also, there is a wealth of online documentation, how-to information, and open source software for the RPi. I hope that some of our readers will give the RPi a try!

Fred, AB1OC

Building An Amplifier

Elecraft KPA500 Amplifier

Elecraft KPA500 Amplifier

I have been planning to add a medium power HF Amplifier to our station for some time now. The plan was to use an amplifier of this type for two purposes –  as an amplifier for Anita’s (AB1QB’s) position at our home station and to have an amplifier that we could take along on DXpeditions and other portable operations. After doing some research, it looked like the Elecraft KPA500 Amplifier would be ideal for this. It is small in size, can operate using either 120 VAC or 240 VAC power and has a quite reasonable weight of 26 lbs.  After dropping some not so subtle hints, I received a KPA500 kit as a holiday gift.

The Elecraft KPA500 is a no-solder kit and requires 4 – 6 hours to assemble. Just for fun, I decided to make a time-lapse video of the assembly, checkout and an initial QSO with our KPA500.

The assembly of the kit was quite straightforward and I was able to complete it in about 5 hours. The amplifier worked fine after assembly. It  performs well on all of the Amateur Bands from 160m – 6m and delivers its rated output of 500 W with 25-35 watts of drive power. The initial QSO in the video was made using our Elecraft KX3 Transceiver which provides a maximum of 12 watts of drive power to the amplifier. As you can see in the video, the KPA500 produces about 200 w output using the KX3. I have also tested the KPA500 with a 100W transceiver and found that it produces the rated output on all of the bands and runs cool and quiet. Testing with my station monitor as well as on-air reports indicate that the KPA500 produces a clean signal.

I know that some of you may be wondering how I made the time-lapse video included in this post. I found a very good how-to webpage that explains how this is done and includes links to some good software choices to perform the various steps in the process. The software and hardware that I used are listed in the credits at the end of the video for those who are interested.

Time Lapse Video Setup

Time Lapse Video Setup

The basic setup requires a digital camera on a tripod that can take a series of still images at regular intervals. My video was created using a Nikon D7000 which took a still frame  every 5 seconds. The video required a total of about 3,900 individual photos to produce a 24 fps video that is about 2:40 minutes long. A combination of Batch Photo Editing (Adobe Lightroom), Time-Lapse Assembly, and Video Editing (Apple iMovie) tools were used to complete the project.

The plan is to couple the KPA500 with Anita’s new Flex-3000 Software Defined Radio (I got a not so subtle hint too). More on the Flex-3000 and its operation with the Elecraft KPA500 will be the topic of a future post.

– Fred (AB1OC)

Feedline Breakout System

Feedline Breakout System

Feedline Breakout System

Since Anita (AB1QB) and I both want to operate at the same time, we are planning to put two SteppIR DB36 Yagis on our tower. These antennas will be connected to a DX Engineering Stack Matching System so that they can be operated together as a 4 over 4 array. The DXE Stack Match can select either antenna individually and connect it to the feedline associated with the array but it does not provide breakout of both antennas onto separate feedlines. We designed and built a custom feedline breakout system to enable simultaneous breakout of both antennas to separate feedlines. This project involved the construction of both a tower mounted box to house a part of relays and a control box for the shack.

This device is inserted between the Stack Match and the antennas in line with the two phasing lines to each Yagi. It is critical that the breakout device provide identical impedance and phasing effects on both phasing lines if the array is to function correctly. To accomplish this, we selected a pair of Tohtsu Coaxial Relays (Model CX-800N) that have very low SWR impact in the HF bands. These were installed in an outdoor utility box that we got from DX Engineering. Only one relay is used to breakout the lower antenna to a separate feedline as the Stack Match can break out the upper antenna to the main feedline for the array. The reason that two relays are needed is to ensure that RF performance of both phasing lines to the two antennas is identical.

Coaxial Relay

Coaxial Relay

The relays require a 24V source to energize them. I built a simple control box for the shack to provide the needed control voltage. The controller includes three switches so that it can be used for additional 24V relay applications in the future.

Breakout Control Box

Breakout Control Box

I wanted to be sure that the Breakout System had good isolation characteristics between the two phasing lines so that the device did not allow a transmitter using one antenna to interfere or possibly damage a transceiver using the other antenna.. The relays we choose have good isolation characteristics which is a good start. To ensure that we have good isolation at a system level, I used an ArraySolutions Vector Network Analyzer (VNA) 2180 to measure the isolation between the various input and output connections in the Breakout System. The ArraySolutions VNA 2180 uses a PC and software to control a measurement unit which can perform one and two port SWR, impedance, loss and phase measurements (many other measurements are possible as well). In this case, we are making a port to port loss measurement.

Isolation Measurement Setup

Isolation Measurement Setup using a VNA

The VNA 2180 has a dynamic range of about 100 dB which means that it can measure isolation up to this level. As you can see from the following screen shot taken with the VNA software, the isolation of the Breakout System is very close to the limits that the VNA can measure. The worst case isolation measurement is about -97 dB on the 6m band. We also use Bandpass Filters when we are both operating and these filters provide an additional 55 dB or more of isolation which means we have a total of about 150 dB of isolation through this path. In the real world, the antennas themselves will likely have much less isolation between them than this so the isolation performance of the Breakout System should be more than adequate.

Isolation Measurement Results

Isolation Measurement Results

We are making good progress towards the planned installation of three of our Yagis on the tower next week. I will provide some additional posts over the next several days covering additional aspects of the preparation for next week.

– Fred (AB1OC)