GRA-UR90-CF Carbon Fiber HF Capacity Hat

The GRA-UR90-CF is a lightweight carbon fiber capacity hat designed for compact HF antenna systems. Its six-rib umbrella structure increases top-loading capacitance without requiring a significantly taller radiator, making it especially useful for portable low-band operation.
Built with genuine Japanese Toray carbon fiber and an M10 × 1.0P interface, it integrates directly with compatible Gabil antenna platforms including the GRA-7350T(C), GRA-RPG, and GRA-AT330T(C).
The GRA-UR90-CF is a top-loading antenna accessory. It is not a standalone antenna, counterpoise, ground plane, or radial system.

Why Choose GRA-UR90-CF?

Portable HF antennas often use shortened radiators to reduce packed size and setup height.
On lower HF bands, however, electrically short antennas may require substantial inductive loading and careful tuning.
The GRA-UR90-CF adds a large conductive structure at the top of the radiator, increasing effective top-loading capacitance without requiring a much taller whip.
This gives portable HF operators another way to optimize compact antenna configurations, especially on lower-frequency bands.
 

Capacity Hat / Top Loading Design

The GRA-UR90-CF is installed above the antenna radiator as a capacity hat.
Its six-rib umbrella structure provides a broad conductive area at the top of the antenna.
Potential benefits include:
  • Increased top-loading capacitance
  • Improved current distribution
  • Reduced inductive loading requirement after retuning
  • Greater flexibility when configuring electrically short HF antennas
  • Compact overall antenna height
It is particularly useful when experimenting with portable antenna configurations on:
  • 80m
  • 60m
  • 40m
Actual tuning and performance will vary depending on antenna design, operating frequency, installation, ground conditions, and surrounding environment.
 

Premium Japanese Toray Carbon Fiber

The GRA-UR90-CF uses genuine Japanese Toray carbon fiber material.
The structural components are manufactured from layered carbon fiber cloth formed under high pressure rather than conventional carbon-filled injection-molded plastic.
The carbon fiber material contains up to 99% carbon content and provides an excellent combination of:
  • High strength
  • High rigidity
  • Low weight
  • Excellent portability
  • Durable field construction
Except for the center hub and connection hardware, the main structural components are made from carbon fiber.
 

Designed for Portable HF Operation

At only approximately 5.3 oz, the GRA-UR90-CF provides a large top-loading structure while remaining easy to transport.
Its modular threaded construction allows the six carbon fiber ribs to be assembled and removed quickly for field use.
Suitable applications include:
  • Portable HF operation
  • POTA activations
  • SOTA activations
  • Field Day
  • Temporary HF stations
  • Compact low-band installations
  • DX field operation
  • HOA-conscious portable setups

Direct Fit with Gabil Antenna Systems

The GRA-UR90-CF uses the Japanese M10 × 1.0P antenna interface used throughout selected Gabil antenna systems.
Directly compatible with:
  • GRA-7350T
  • GRA-7350TC
  • GRA-RPG
  • GRA-AT330T
  • GRA-AT330TC
  • Compatible Gabil M10 × 1.0P antenna systems
For additional installation options, a Gabil M10 × 1.0P to 3/8"-24 adapter can provide mechanical compatibility with suitable 3/8"-24 antenna systems.
Always install the GRA-UR90-CF on the radiator / top-loading side of the antenna system.

Product Specifications

Model: GRA-UR90-CF
Product Type: HF Capacity Hat / Top Loading Accessory
Rated Power: 400 W
Weight: Approx. 5.3 oz (150 g)
Expanded Size: Approx. 37.8 × 37.8 × 41.7 in (96 × 96 × 106 cm)
Packed Length: Approx. 21.9 in (55.5 cm)
Interface: M10 × 1.0P
Main Structure: Japanese Toray Carbon Fiber
Configuration: Six-Rib Umbrella Structure
Recommended Use: Portable HF Top Loading
 

Important

The GRA-UR90-CF is not a standalone antenna.
It is designed as a capacity hat / top-loading accessory and must be used with a compatible antenna system.
It is not designed to function as an RF counterpoise, artificial ground, ground plane, or radial system.
After installing the GRA-UR90-CF, always retune the antenna and verify SWR before transmitting.

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