At 13.4 turns per inch, a 6-inch winding window gives you exactly 80 turns to work with. This is actually a fantastic number — it hits that target estimate for Band 2 perfectly without cramming.
Before mapping out the turns, let's address your question about the currents and tap wires, because it fundamentally simplifies your build.
## Receive-Only Current Levels
In a receive-only antenna system, the currents are microscopic. Even if a massively strong local AM station induces a 10-millivolt signal across the 400-ohm input of your SX-28, the current flowing through that secondary is only 25 microamps ($I = \frac{V}{Z}$).
Because the current is virtually zero, wire gauge for the taps does not matter for electrical load. You will not melt or overload even the finest wire you own.
The only constraints on your tap wires are mechanical strength and RF layout:
1. Fragility: Very fine wire breaks easily when soldering or plugging/unplugging banana jacks. 2. Shorting: If you use bare (uninsulated) copper wire, the 1-to-2-inch runs from the coil to the banana jacks must be physically rigid enough that they cannot accidentally bend and touch each other, which would short out sections of your coil.
If your fine bare copper wire is stiff enough to hold its shape in the air, use it. If it is too floppy, you might be better off stripping the insulation off some thicker scrap wire just for the tap standoffs.
## The 80-Turn Symmetrical HF Design
To cover Bands 2 through 6, we want small turn increments in the center for the high frequencies (where small changes in inductance matter a lot), and larger turn increments on the outer edges for the lower frequencies.
Here is the exact layout to distribute your 80 turns symmetrically across the 6-inch space:
| Section | Turns per Side | Cumulative Turns (Total) | Target Frequency Range | | --- | --- | --- | --- | | C (Center) | 4 left + 4 right | 8 | Band 6 (21–42 MHz) | | M1 & P1 | 4 | 16 | Band 5 (11–21 MHz) | | M2 & P2 | 6 | 28 | Band 4 (5–12 MHz) | | M3 & P3 | 10 | 48 | Band 3 (2.5–5 MHz) | | M4 & P4 | 16 | 80 | Band 2 (1.6–2.5 MHz) |
## How to Wind and Tap It
1. Mark the Center: Draw a line dead center on your 7-inch PVC pipe. Your "C" section will be 4 turns to the left of this line and 4 turns to the right. 2. Continuous Winding: Do not cut the wire at the junctions. Wind the coil continuously. 3. Creating the Taps: When you reach a junction (e.g., after the 4th turn of M1), use a hobby knife to carefully shave a tiny bit of the silicone jacket off the top of the wire, tin it, and solder your stiff tap wire directly to it. Then continue winding the next section. 4. The Primary Placement: Your primary winding will go directly over that 8-turn "C" section in the middle, separated by a wrap of Kapton tape, electrical tape, or even paper to provide a dielectric gap.
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Last modified: Monday, 10 Aug 2026