#Microwave imaging using portable "Tailgater" satellite antenna.
Gabe Emerson / Saveitforparts 2023. Email: gabe@saveitforparts.com Derek Shaheen / dshaheen/@/pm.me
Video demo: https://youtu.be/lVOTZxNCgTM
Introduction:
This code controls a portable satellite antenna over USB using serial commands. The dish_scan.py program aims the dish to a selected portion of the sky and records the RF signal strength. The dish_image.py program reads the resulting data and creates a heatmap of the scanned area. Frequencies using stock Tailgater antenna hardware will be in the Ku band (~11ghz)
Please note that the author is not an expert in Python, Linux, satellites, or radio theory! This code is very experimental, amateur, and not optimized. It will likely void any warranty your Tailgater antenna may have. There are probably better, faster, and more efficient ways to do some of the functions and calculations in the code. Please feel free to fix, improve, or add to anything (If you do, I'd love to hear what you did and how it worked!)
Applications:
- Imaging geostationary TV satellites
- Surveying an environment or room for microwave radiation
- Imaging an environment using ambient or reflected microwaves from Ku band source
- Imaging other wavelengths with a different feedhorn or LNB (not tested)
- Integration with an SDR and other antenna elements (not tested)
Hardware Requirements:
This code has been developed and tested with a Dish Network "Tailgater" portable satellite antenna. Specifically, a 2014 version in an octagonal-ish enclosure with a USB "A" connector on the mainboard (located inside the enclosure, behind the dish reflector). There are many variations, models, and versions of this antenna, including Wallace, VuQube, Dish, King Controls, etc. I have not found a consistent model numbering scheme, so I don't know how to identify the correct model without opening the top and looking for a USB port. Other models have USB mini or other ports, and some appear to have jumpers for 9-pin serial. I have not tested this software on any of those variations.
My test unit uses firmware version "pragelato.h 704 2013-08-09 03:41:27Z rudrava" Other versions may have different console commands available.
This code has been tested sucessfully on a range of Linux PCs, from 686-class using a low-resource distro, to higher-end running a modern distribution.
Notes on power supply:
The USB connection only provides data to/from the dish. Power for the board, LNB, and motors comes from the coax "F" connector. This needs between 13-18V DC, center pin positive. Normally this is provided by a set-top box or satellite reciever. Power can also be provided by an in-line injector for powered antennas, a meter such as V8 Finder, or simply a DC adapter wired to a coax cable. Providing 13V will tell the LNB to use vertical polarity and 18V will use horizontal polarity.
Package Requirements:
dish_scan.py uses the numpy, pyserial and regex packages. dish_image uses matplotlib. They can be installed individually or by running "pip install -r requirements.txt"
Setting up / testing Tailgater console:
To connect to a Tailgater antenna with USB A port, you will need an A-to-A cable (available online).
You can check for proper connection by running "lsusb" on Linux. The dish should show up as "Microchip Technology, Inc. CDC RS-232 Emulation Demo".
Run "dmesg | grep tty" to see which port the dish is using. This is usually something like /dev/ttyACM0, although I have seen it jump to ttyACM1 or ACM2 if the power or USB connection are interrupted. If your Tailgater is NOT on /dev/ttyACM0 you will need to edit line 15 of dish_scan.py to reflect the correct port.
To connect to the serial console on the dish, run "screen /dev/ttyACM0" (or appropriate port) on Linux, or use a Windows serial terminal to connect to the usb device (typically com3 or similar). You will initially get a blank screen. Typing "help" should return a menu of available commands and a "GO>" prompt.
Note that the console does not accept backspace, so if you make a mistake while typing, just hit enter to clear the console. If necessary, close the console or unplug the dish to avoid a motor overrun.
Positioning the dish:
The Tailgater dish uses a 360-degree counter-clockwise coordinate system, with the coax / F connector as "North" / 0 degrees. The dish considers an azimuth of 90 to be 90 degrees counterclockwise from the coax jack (looking down at the dish from above). Azimuth 180 is directly opposite the coax jack, and azimuth 270 is 90 degrees clockwise from the RF jack. This is technically "backwards" from a standard compass heading. The code is written to take this into account, but please note that image and array outputs will show azimuth in the dish's reference plane, opposite of standard compass or orbital azimuth.
Generally I place the dish with the coax connector facing due North (for scans of the Southern sky), but you can place it in any orientation you want. The dish scans left to right, incrementing up from the starting elevation. Remember the coordinate system is "backwards" compared to standard compass headings.
Running a scan:
Once the dish is connected, powered, and ready on a USB port, run: "python3 dish_scan.py" You will be prompted for the starting and ending azimuth and elevation of your scan. Valid azimuth range is 0-360, and valid elevations are 5-70 degrees (outside of these values may overrun the motors). If you enter a value outside the valid range, the program will use the minimum or maximum as appropriate. The default values are from azimuth 90 to 270 (West to East in the dish's coordinate system), and from elevation 5 to 70 degrees. This covers most of the Southern sky (if the dish is placed with coax jack aiming due North). A scan with default values takes approximately 3.5 hours due to the minimum rfwatch runtime of 1 second. Scans of smaller azimuth/elevation ranges should take less time. Estimated scan time for your parameters will be shown once the scan starts.
During the scan, the current azimuth, elevation, and signal strength will be displayed for each dish position. A preview image, "result-.png" will be created and will update live during the scan. On Gnome Image Viewer, this file should automatically refresh as it updates. It will be very small (x pixels equal to your scan's azimuth range, and y pixels equal to your scan's elevation range). However, it should be enough to get an idea if the scan is working.
Generating an image from a scan:
Once a scan has completed, you will have three output files with the same timestamp:
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"result-.png" The low-resolution preview image.
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"raw-data-.txt" The raw scan values in a numpy array.
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"scan-settings-.txt" The scan parameters (start and end azimuth / elevation)
dish_image.py will use the two text files to create a heatmap of your scan. Run the code along with the name of the raw-data scan you want to process. For example: "python3 dish_image.py raw-data-20230322-153935.txt"
The code will load the corresponding scan-settings file automatically, and opens a heatmap of the scan in a new window. You can save this heatmap for later use.
I noticed an issue where counterclockwise rows were offset slightly from clockwise rows, this seems to be a combination of indexing and inconsistencies with motor movements. The fix_image.py script is an alternate version of dish_image that outputs a better bitmap from scans run with my dish. It does this by shifting every other row in the signal strength array 3 places to the right. Each Tailgater unit might be a little different, and the range of elevation values can alter this offset. You may have to play with the last number on line 38 to get the best image.
Example Images: I have included several example images to show what a scan looks like:
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"dish_image example.png" The result of running a default scan with dish_scan.py and processing with dish_image.py. Shows geostationary TV satellites.
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"satellite overlay.png" The previous file overlaid on a panoramic photo of the same area. Note that trees, roof overhangs, and power poles are visible in RF.
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"satellite preview.png" A scaled-up version of the "result" preview generated during a scan.
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"room overlay.png" An overlay of a default scan run indoors, showing microwave RF coming from a poorly-shielded PC tower (lower right).
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"house.png" A structure scan comparing KU band (with "hsv" colormap), visible light, and 50% overlay of each.
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"tailgater.png" Example of the antenna unit used for this project.
Example Files
I have included some example data files output by dish_scan.py, for processing with dish_image.py
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"raw-data-20230321-193653.txt": numpy matrix of signal strength at each azimuth and elevation pair
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"scan-settings-20230321-193653.txt": scan parameters for dish_image to use when processing
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"result-20230321-193653.png": Preview image created by dish_scan (not used by dish_image)
Additional notes:
The dish_scan.py code contains code for two resolution settings, however the high setting does NOT currently work with my dish due to motor drift. Low resolution (default) uses azangle and elangle commands on the Tailgater console, so each scan position is one degree. The high- resolution version would have used the "nudge" commands available in the Tailgater console. However, these do not seem to be consistent in each direction, so the dish drifts off center over the course of a scan and causes a distorted image. Currently the "resolution" setting is disabled, you can re-enable it by un-commenting lines 61-64 and commenting out line 66. Do so at your own risk of frustration and possibly hitting motor limits.
The heatmap generated by dish_image.py uses CMRmap. If you wish to use another colormap, you can change line 67 of dish_image.py. I also like "seismic" and "gnuplot2", but I feel that they lose some definition on the background landscape. "hsv" may also be useful for noisy scans.
If you use this code and encounter any problems, feel free to email me at the address at the top of this file. However, I may have to refer back to this myself to remember how it works!