Notes, Changes, and Errata on v0.1

Added by J. Simmons over 8 years ago

The following are comments from Aaron concerning lessons learned from v0.1. For reference, see the v0.1 Assembly Instructions

  1. We discovered that the steel sleeve over the preamp and the base does little to keep the noise out, particularly when it is not grounded itself. Instead it makes a conduit for static discharge to the ground of the preamp which could damage the preamp.
  2. The 1 ¼” and 1” size of the antenna body and base are excessive for the 915MHz version. It would be better to mount the preamp horizontally in a base and reduce the size of the antenna body to ¾” or even ½”.
  3. As the ground plane is quilted, it pillows the fabric, particularly the stiffer conductive fabric disk (ANT14). This reduces the radius of the ground plane and circumference by a set amount per stitch, but since the circumference is about 6 times the length of the radius, the shrinkage is 6 times greater in the radius than in the circumference. This causes the ground plane to become floppy even when stretched taught by the struts. A better solution is to secure the conductive fabric with a minimum number of stitches.
  4. The struts (ANT17) do little to keep the ground plane flat, primarily because of the issue noted above, and that the struts cover very little of the ground plane assembly’s surface. A better solution is to use a semi-rigid plastic mesh to support the ground plane over the whole surface.
  5. If a plastic mesh is used to support the ground plane, it could be affixed using a minimum of stitches and/or an adhesive to secure the conductive fabric to the surface of the mesh. Further, the mesh could be silk screened with a logo or a decal applied with little to no performance loss. We should experiment with this concept.
  6. The RF line and phasing loop mounted to the outside was convenient for testing, but made the Mk1 prototype more fragile than practical for a production model. Bringing the RF line up from the bottom and the phasing loop in from the top on the inside would be much more rugged. The only outside connection should be the pigtail from the ground plane. To fit in a ¾” or ½” antenna body, the phasing loop would have to be tightly coiled and covered in heat shrink to keep it’s shape during assembly and parts storage.
  7. Use pre-terminated coax lines for the amplifier line (ANT11) and the preamp output (ANT12) rather than soldering them to the preamp for improved reliability.
  8. Build the preamp with SMA connectors rather than solder the coax from the amplifier line (ANT11) and the preamp output (ANT12). These can be machine soldered, while the coax cannot.
  9. The preamp (RAD02) can be powered with a power inserter, but this would add cost to the completed ground station and may induce noise. Experimentation should be performed to help understand the pros and cons.
  10. A jig can be made to precisely cut and strip the phasing loop (ANT13) once the ideal measurement is identified.
  11. With smaller diameter components the assembly can be cleaner, cheaper, and have better repeatability.
  12. With a plastic mesh backed ground plane assembly, the completed ground plane can be sandwiched between two sections of plumbing components used for the antenna body and secured there with PVC cement for ease of assembly.