RQ: Specifications for 500 kHz top hat antenna

[D.J.J. Ring, Jr.]

From:  Sverre Magnus Berg, LA6ZX

Hello sparks, I am looking for data/specifications for this top loaded (umbrella) HF antenna. I have had this transmitting antenna on two of my vessels with STK/Alcatel stations. There must be an archive somewhere in the EU, and my best guess is that some old timers from DEBEG or Radio Holland knows about this antenna. I am doing antenna simulation as a hobby, and are just curious how well this antenna performed. The picture below is from the museum ship Cap San Diego in Hamburg.

73

Sverre Magnus Berg

LA6ZX

[Jerry Proc]

On 2025-08-04 2:42 p.m., D.J.J. Ring, Jr. wrote:

top loaded (umbrella) HF antenna

--

Here is what CHATgpt had to say about this HF antenna.

 

A top-loaded (umbrella) HF radio antenna is a type of vertical antenna that uses wires sloping downward from the top of the vertical radiator to form a structure resembling an umbrella. It's designed to increase effective height and radiation efficiency, especially at lower HF frequencies where a full-size quarter-wave vertical would be impractically tall.

---

🔧 Basic Structure:

1. Vertical Radiator:

   • A single tall vertical element (often a mast or wire) acts as the main radiator.

   • It connects to the transmitter via a feedline at its base.

2. Top Loading Wires ("Umbrella Wires"):

   • Several wires extend outward and downward from the top of the vertical.

   • They are usually connected together and electrically tied to the top of the vertical element.

   • These wires do not radiate much themselves, but act as a capacitive top hat, increasing current in the vertical portion.

3. Ground System:

   • Radial wires are spread out along the ground to form a counterpoise or connected to actual ground rods.

   • Essential for proper performance.

---

📡 Purpose of Top Loading:

• Electrical Lengthening: Makes the antenna appear electrically longer than its physical height.

• Improved Efficiency: More current is concentrated in the vertical section, which improves radiation efficiency, especially for low HF bands like 160m (1.8 MHz) or 80m.

• Reduced Physical Height: You get good performance without needing a very tall mast.

---

📏 Example:

A full-sized 1/4-wave vertical antenna for 160 meters would be about 40 meters (130 feet) tall. A top-loaded version could use a 15–20 meter mast with umbrella wires to simulate the full length.

---

✅ Advantages:

• Effective on low bands like 160m and 80m.

• Requires less vertical height.

• Simpler to erect than a full-sized vertical.

⚠️ Considerations:

• Needs space for umbrella wires and ground radials.

• Top loading doesn't radiate — it's only for capacitive effects.

• Mechanically more complex than a straight vertical.

Regards, Jerry Proc E-mail: jerry...@sympatico.ca Web: jproc.ca