The G5RV antenna has been discussed for decades, so there’s little point repeating the theory behind it. Instead, this project focuses on something less common — adapting the classic G5RV concept for operation on the 2 meter amateur radio band around 145 MHz.
The idea started as a simple experiment. I wanted an antenna that could be packed easily, carried onto a hill, and assembled in minutes for portable VHF testing. The dimensions of this version make that surprisingly practical.
Unlike many multiband antennas, the G5RV antenna 2 meters is not designed as a conventional half-wave dipole on its highest operating frequency. In this configuration, the antenna behaves as a 3λ/2 center-fed system. That detail changes the matching requirements and makes the feed section especially important.
G5RV Antenna : Matching Section and Feed Line
For operation on 145 MHz, the matching section uses a 360 mm length of standard 300 ohm TV twin lead. The black perforated type with cut-out windows is preferred because it generally produces more stable electrical characteristics and lower losses.
If ordinary solid TV twin lead is used, the shortening factor must be taken into account. Depending on the cable type, the factor typically falls between 0.8 and 0.9. Ignoring this correction shifts resonance noticeably at VHF frequencies.
The twin lead acts as a 1:1 impedance transformer. It allows direct connection to either a 75 ohm balanced line or coaxial cable in the 50 to 80 ohm range while still maintaining an acceptable standing wave ratio.
To match properly with a 50 ohm coaxial cable, the feed point should be placed approximately 34 to 36 mm from the shorted end of the twin lead section. Small adjustments in this area can noticeably affect the final SWR.
Antenna Dimensions
The prototype used a 360 mm matching section simply because no longer piece of twin lead was available at the time. With that configuration, each dipole arm measured 1,050 mm.
A different arrangement is also possible. Using a quarter-wave matching section of approximately 430 mm changes the required dipole arm length to around 980 mm.
The antenna was designed specifically for 145 MHz, with dimensions calculated from the standard formula for a 3λ/2 radiator system.
Measured Performance
Field tests produced encouraging results. A standing wave ratio of 1.1:1 was measured at 144.3 MHz, while the SWR increased to approximately 2:1 at 145 MHz. For a lightweight experimental antenna, that performance was more than acceptable.
Measured gain appeared to be around 3 dB, although some variation was observed between horizontal and vertical polarization. That behavior isn’t unusual at VHF, especially with portable installations where antenna height and surrounding terrain can influence results.
An interesting compromise arrangement was also tested with one dipole arm mounted vertically and the other horizontally. The antenna remained usable, though the gain dropped closer to the level normally associated with a Slim-Jim antenna.
Practical Notes from Testing
One thing became obvious during portable operation: simplicity matters. This antenna folds easily, weighs very little, and requires only basic materials that most radio amateurs already have in the workshop.
The feed system is also forgiving enough for experimentation. Small adjustments to the twin lead length or feed point spacing can help fine-tune resonance for local operating preferences. That flexibility makes the design attractive for field use, emergency setups, or casual hilltop operation.
While this version of the VHF G5RV antenna won’t replace a dedicated high-gain VHF antenna, it offers a surprisingly effective alternative for operators who enjoy experimenting beyond conventional designs.
According to Alexander Karakaptan, UY5ON, the concept demonstrates that even well-known HF antenna ideas can still produce interesting results when adapted creatively for VHF use.
Related Posts
- 5/4 Wave VHF Antenna for 145 MHz Using 450-Ohm Ladder Line
- 3-Element Yagi antenna for 70cm UHF band
- FM Bazooka Antenna for Superior FM Radio Reception (88–108 MHz)
- Slim-Jim Antenna for FM Broadcast Band reception (88–108 MHz)
- Understanding the Bazooka Coaxial Dipole Antenna Design
- Stacked 5/8-wave VHF Antenna for 146 MHz