I Need Help #2

I was having trouble making sense of something so I started another 'I need help' page.

It started out about my attempt to match my far-from-optimum antenna to my #7 radio which works but not very well. I learned that if excellent sensitivety for an SX-28 is 2‐4 µV, my radio is about 35 µV. And that's just a guess.

Having some stuff laying around and wanting to keep my hands busy while sitting on the porch shooting the breeze with my lovely wife, I made this:

I didn't have any plans to follow and I don't know a whole lot about this sort of thing so I was going with something like "The box is 7½ inches wide inside so let's start with 7 inches of ½ inch PVC."

"Let's wrap a bunch of enameled 26 AWG around it and put a bunch of taps on one end since we have no clue what the antenna impediance is and we think the radio is 400 Ω"

"Let's put some sticky tape on it and make another winding using 18 AWG and space the turns out a bit."

I am not joking.

Here's where it got weird. When I connected the box up one way - red to red, black to black, etc - it worked OK and I could pick up some stations. When I reversed one of the windings, it didn't work at all. I didn't understand this. Turns out there's a lot I didn't understand.

I decided to ask Google's Gemini AI Large Language Model (LLM) and embarked on a wide ranging conversation that started with the box above (apparently I'm a genius or Gemini is a schmoozer) and wound up touching on all sorts of other topics.

The conversation is very long and is getting longer.

I've sliced the conversation into pieces in the form I've used elsewhere on this website. They are not discrete questions - one depends on what has transpired before. The items below are the prompts with links to the responses. The 'first', 'second', 'third' bit records the order in which I asked the questions. That's important.

Since the conversation wanders all over the map, I wanted to come up with a scheme that sorted the mess out. Seperate pages were considered and rejected. I opted for background colors to indicate what was going on. Pink means it's a bad answer or the prompt is addressing a bad answer¹. You can pretty much skip over these. There might be some good bits in them which will be pointed out in italic comments. Yellow means its about the subject that got us here - the box.

The start of the discussion of why the radio does so poorly. The mention of the 462 KHz crystal is root of the issues. As it turns out later, it's not really 462 KHz and since the radio is aligned to that bogus number, everything is pooched.

18th prompt: I need to make major corrections to the '150-turn' coil. First, its 302 turns of 22 AWG wire wrapped around a length of one half inch PVC water pipe. There are taps at 197, 237, and 270 turns. It is wound counterclockwise per your question. The winding is single layer with no space between turns. Dimensions of the '30-turn' coil to follow

First of these three used the wrong wire guage.

19th prompt: I need to correct a typo - the wire gauge is 26, not 22

Fot reasons unknown, Gemini was using a length of 5 inches instead of 4.5

20th prompt: The total length of the 302 turn coil is 4.5 inches

This is the corrected response that started out with "That is a massive correction, and it changes the entire physics of what you have built!"

21st prompt: 67 turns per inch exactly matches my calculation. To wind the other coil, I put 3 pieces of double sided compressible foam tape along the outside of the 302 turn coil to hold the next coil in position since it is not closely spaced. There are 28 turns, also counterclockwise², evenly spaced over the 302 turn coil. I connect the antenna to the 28 turn coil and the radio to the 302 turn coil. Selecting which tap to use does influence the quality of reception on the AM band.

"That changes the entire behavior of the transformer! Since both the 302-turn secondary and the 28-turn primary are wound counterclockwise, you have built an in-phase (additive) transformer"

From what I gather, once the crystal is sorted out (properly measured, circuit adjusted), the IF strip adjustment takes precidence over everything else.