Here’s a clear, color-schematic of a Delta Loop VHF antenna for ~145 MHz, showing all critical dimensions and construction details. This version is based on the original design by F6KFT (see article on f6kft.free.fr).
A Delta Loop VHF antenna is a triangular loop antenna, often used for VHF-bands because it can provide good gain, relatively simple construction, and a clean radiation pattern. The loop in this case has one side horizontal (A), and the other two sloping downwards (sides B and C) to a feed point near the bottom. A coaxial cable feeds the loop, via a small connector.
In VHF, the delta loop’s broad bandwidth, low noise reception, and relatively simple construction make it attractive for amateur radio operators and experimenters.
Dimensions & Parts (for 145 MHz)
- A (top horizontal side): ~ 480 mm
- BC (sum of the two sloping sides B + C): ~ 790 mm
- D (vertical offset from feed point to reference line): ~ 20 mm
- Additional small spacing of 15 mm at the connector region, for mechanical or insulating clearance
These are exact values for 145 MHz as per the diagram. If you design for another frequency, scale proportionally (wavelength × factor).
Construction Details
- The loop is triangular (“delta”) in shape.
- The feed point is at the bottom vertex, using a connector block.
- A coaxial cable carries the signal from the feed point: the inner conductor connects to one leg of the loop, and the outer conductor (shield) to the other.
- Proper spacing (15 mm) at the connector helps prevent electrical contact or arcing, especially if this is outdoors and exposed to elements.
Why Choose a Delta Loop?
- Flexibility: Mount horizontally for horizontal polarization or vertically for vertical polarization.
- Low Noise: Particularly in urban environments, loops tend to pick up less man-made noise than verticals.
- Improved DX: Broadside radiation pattern and low angle of radiation can improve long-distance VHF contacts.
This design is derived from F6KFT, article 183 on http://f6kft.free.fr/spip.php?article183&lang=en — many thanks for the detailed original layout and measurements.
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