Sunday, January 17, 2021

QO-100 Up-Link -- So Many Things Wrong

There are so many things wrong with my up-link feed:

  1. RG-6 75 Ohms feed line from a 50 Ohms PA
  2. the base of the helix is embedded in hot-glue
  3. the material is Zn-plated Cu-wire (Zn corroding)
  4. the spacing of the helix is off and narrows towards the end

2.4 GHz up-link helix feed

You are seeing the result of ignorance and tweaking, which resulted in the feature of point 4).

I hooked a nanoVNA2 up to the PA side of the RG-6, then pushed and pulled on various parts of the helix to minimize the SWR. This procedure included the 75 Ohms transmission line of course. Thereby, I improving the SWR from 4.6:1 to 2.4:1.

Next step you probably be to play with a wire-cutter again. As you can see, the helix has 3+3/4 turns, so, there might be room for improvement still.

For the time being, I am pretty happy with my up-link signal anyway.