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Project Idea - Self-Orienting Antenna

nbuuck

This is an idea that I'm hoping to pursue. The goal is to build a chassis that hosts a self-orienting amateur radio antenna (the application of the antenna is not critical). Some of the requirements I'm designing to meet:

 

  1. In this case, the chassis must adjust to fit a 2008 Subaru Forester's cargo racks (not terribly relevant to this site, but a requirement none-the-less).
  2. The system will receive input from a NMEA-compliant GPS receiver.
  3. The system will receive the GPS coordinates of the target transmitter (likely a repeater, but any amateur station).
  4. The system will orient the antenna on the horizontal axis exclusively.

 

Design considerations:

 

  1. An approximately-square board will serve as the base for many of the functional components of the system.
  2. On the top side of the base board, a pinion wheel will host the mount for the antenna.
  3. An adjacent pinion wheel will interlock with the antenna wheel.
  4. The axis of the second pinion will be driven by a motor on the underside of the board.
  5. The motor will be controlled via an onboard FPGA (some brief research shows that the Arduino may be an appropriate solution).
  6. An NMEA GPS receiver with an onboard antenna will be mounted clear of the radio antenna on the topside of the vehicle.
  7. A four line connection from the GPS receiver will connect it to TTL inputs on the FPGA.
  8. The FPGA will calculate the optimal orientation of the antenna by calculating the angle between the orientation of the receiver and the coordinates of the target station.
  9. The target station will likely be specified through some form of practical manual inputs; not sure what the best way to approach this is.
  10. Like Ben's recent vehicle-mounted camera controller project, the system will need to zero out the orientation of the antenna on initialization.
  11. Some form of learning on the part of the program may be required in order to determine direction of travel before orienting the antenna.

 

I just figured I'd share this project since TBHS has been the primary inspiration for the project. Maybe some of you have some ideas about how to practically input the GPS coordinates that the antenna should orient itself toward?

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  • Alright, for the prototype, I'm going to try a pair of knobs with rheostats and use the resulting voltage to divide possible ranges of GPS coordinates (Lat: +-90, Long: +-180). Each rheostat's effective 0 point will have to be calibrated to 50% of its travel to represent the valid range of GPS coordinate components.

  • in reply to nbuuck

    Why not just use 4 antennas and have one in North East South West and have them tethered.

  • in reply to e14 Contributor

    It sounds like an interesting suggestion, but I can't really find any background information on the topic.

  • Have you considered having the controller run the antenna though a (scan) rotation derived from the gps whilst logging the signal/noise. and using the result to align the antenna in the best direction? Once locked in, directional data from the gps could make adjustments to the rotation, keeping it pointed in the right direction.

  • in reply to e14 Contributor

    I thought of the same approach.  It ties up less RF hardware than going with the four antennae approach.  The key to making it work would be to have a solid signal on during your scan time so you could get the bearing on the strongest signal.

    The Germans used this approach with a manual scan to find hidden resistance transmitters all over Europe duing the Second World War.

     

    You might be able to get a faster lock on time with a two antenna system on a rotating wheel, because the two signals will enable you to get a good bearing to the signal source with only a 180 degree scan, but again, it uses more RF hardware.  Still, the two antenna approach would also help you quickly determine which direction the source changes from your current position and be much faster at keeping you locked on the source.  That immediate deviation measurement might make it worth going the two antenna route.  With a single antenna, you would have to spend more time scanning to see which direction the source changed.  That problem could force you to go through some rather complex search and track software.

     

    Just a thought.

    DAB

  • I've worked on systems that do basically the same thing as you want though they were mounted on ships for high speed data links.  What you want to do is easier in some points and harder in others.  The antennas I worked on would seek the desired signal and then lock onto it.  You don't have a constant signal to lock onto an amateur transmitter most of the time,

     

    If you have the coordinates of the antenna and a GPS with an electronic compass in the car it's simple to calculate bearing and have the antenna orient from a relative bearing based off the direction the car is facing.  You don't need an FPGA, it's overkill for the task.  I'd use a bare micro, but an Arduino will be sufficient to just calculate a bearing.

     

    You could mount the GPS and compass to the antenna mount itself but that exposes a lot of electronics unnecessarily.  You should just be able to pass it a relative bearing and have it orient itself  from a forward facing reference just to keep things simple.  That will give you more flexibility in designing the backend to calculate those bearings.  You can use a heavy duty commercial rotor or build something to rotate the antenna though it needs to be robust enough to handle the wind load if you're not going to put a fairing on it.

     

    As for a location database I'd use something like a microSD card with a CSV file that contains the callsign of the antenna and location.  You can mount a small keyboard and lcd and punch in the desired repeater.  If it's mobile you could probably use APRS to get the location data.

  • in reply to e14 Contributor

    If it's a permanent mount, get an RV TV antenna that has 12v rotation.  There may already be a product that auto-adjusts the antenna, or simply an omni-directional one.

  • Have you considered a doppler scanning array, such as used by Lojack on police cars?  4 elements could be electronically rotated to determine direction, then be used as a phased array.  This would have no moving parts, an important consideration for mobile use.  You never mentioned frequency(ies) of operation.  Am I safe in assuming 2 meters?  How much gain and directionality are you looking for?

     

    Mike wd6ehr