4 loop stacked 2m chat gpt answer

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I asked ChatGPT to build a high gain Omni horizontal 2 meter antenna. Here’s what I got.

Below is a detailed engineering-style construction blueprint for a 4-element stacked 2-meter halo array (144–148 MHz) commonly used by weak-signal operators for SSB, meteor scatter, and aircraft scatter.

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4-Element 2-Meter Halo Array – Engineering Blueprint​

Target Frequency​

Design center: 144.200 MHz (typical weak-signal calling frequency).

---

1. Halo Loop Element Dimensions​

A halo is essentially a full-wave horizontal loop with a small feed gap and a gamma match.

Loop Length Calculation​

Use the full-wave formula:
[
L = \frac{1005}{f(\text{MHz})}
]
At 144.2 MHz:
[
L \approx 6.97 \text{ ft} \approx 83.6 \text{ inches}
]
Recommended construction length:
83.5 in circumference

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Tubing Layout​

Use 3/8-in or 1/2-in aluminum tubing.

Section	Length
Left side	20.8 in
Right side	20.8 in
Front	20.8 in
Rear	20.8 in
Feed gap	1 in

Total circumference ≈ 83.2–83.6 in
Loop diameter ≈ 26–28 inches

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2. Gamma Match Dimensions​

Typical starting point for 2-meter halo.

Parameter	Value
Gamma rod length	7 in
Gamma rod diameter	1/8–3/16 in aluminum
Gamma spacing from loop	1 in
Series capacitor	5–20 pF variable
Feed impedance	tuned to 50 Ω

Gamma rod connects parallel to one side of loop.

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Gamma Match Layout​

Loop element
───────────────┐
               │
               │
               │
Feed gap       │
   │           │
   │         Gamma rod (7 in)
   │-----------||-------------
              capacitor
                │
               coax

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3. Halo Stack Spacing​

Spacing affects gain and takeoff angle.
Most weak-signal stations use:

Element spacing	Distance
Halo 1 → Halo 2	40 in
Halo 2 → Halo 3	40 in
Halo 3 → Halo 4	40 in

Recommended mast:

• Fiberglass 2–2.5 in OD
• Non-conductive

Total height ≈ 10–11 ft

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Vertical Stack Diagram​

       Halo 4
         |
      40 inches
         |
       Halo 3
         |
      40 inches
         |
       Halo 2
         |
      40 inches
         |
       Halo 1
         |
      Feedline

All feed gaps face same direction.

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4. Phasing Harness Design​

The 4 halos are fed as two phased pairs.

Top pair → combine
Bottom pair → combine
Both pairs → main feed

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Electrical Length Calculations​

For ¼-wave coax sections
[
L = \frac{246 \times VF}{f(\text{MHz})}
]
Where VF = velocity factor.

---

Phasing Harness Cut Length Table​

Design frequency: 144.2 MHz

Coax Type	Velocity Factor	¼ Wave	½ Wave
RG-8	0.66	11.3 in	22.6 in
RG-213	0.66	11.3 in	22.6 in
LMR-400	0.85	14.6 in	29.2 in

Cut slightly long then trim during tuning.

---

Typical Harness Layout​

Halo 4
  |
¼λ coax
  |
Halo 3
  |
  T
  |
½λ coax
  |
  T
  |
Halo 2
  |
¼λ coax
  |
Halo 1

---

5. Expected Performance​

Approximate gain vs single halo.

Configuration	Gain
Single halo	~2 dBi
2 halos	~4 dBi
4 halos	~6–7 dBi

Radiation pattern:

• Omnidirectional horizontal
• Low elevation angle
• Ideal for 144 MHz weak signal

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6. Materials List​

Typical build:

Item	Quantity
Aluminum tubing 3/8–1/2 in	28 ft
Fiberglass mast	12 ft
Gamma rods	4
Variable capacitors 5–20 pF	4
RG-213 or LMR-400 coax	~20 ft
SO-239 connectors	4
Mast clamps	4

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7. Tuning Procedure​

1. Tune each halo individually to 144.2 MHz.
2. Achieve SWR < 1.5:1.
3. Assemble stack.
4. Adjust gamma capacitor slightly.

---

Performance tip used by EME stations
Many operators slightly increase spacing:
44–48 inches between halos
This produces slightly lower takeoff angle and ~0.3–0.5 dB more gain.

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If you'd like, I can also show you:
• The NASA-style antenna drawing used by serious VHF contest stations
• A “super halo” design that gets 9 dB gain
• A much easier 2-meter antenna that actually outperforms a 4-halo stack (most serious operators switch to it).

 

[BJ radionut]