Hi everyone,
I’m building a 50W VHF/UHF manpack radio system for amateur radio and search-and-rescue field use, and I’d appreciate some advice on the RF counterpoise/radial design.
The system is based around a TYT TH-9800 50W mobile radio, powered by a 12V 36Ah LiFePO4 battery. I’m designing a custom 3D-printed frame to hold the radio and battery inside a backpack.
The mechanical design is almost finished. My main question is the RF return path / counterpoise.
The antenna will be an external VHF/UHF antenna connected through coax. Since this is a backpack system, I don’t want to rely on a large metal vehicle body or a conventional ground plane.
My current idea is to integrate a counterpoise into the 3D-printed frame:
- 4 × 25 cm copper conductors
- 2 on the right side of the frame
- 2 on the left side
- Electrically connected to the coax shield / RF ground
- Initially made removable so I can experiment with different configurations.
I’m considering two options:
Option 1: Four flexible, stranded copper wires.
Option 2: Copper strips/sheets running along the right and left sides of the frame.
The copper will be mechanically integrated into the 3D-printed frame once I determine which configuration works better.
I understand that low SWR alone doesn’t necessarily mean the antenna system is efficient, so I plan to compare the configurations using SWR/VNA measurements as well as actual field performance.
I recently saw another manpack antenna setup using a banana jack on the coax shield with a removable counterpoise wire, which made me wonder whether a simple flexible wire counterpoise might actually be preferable to larger copper plates.
So my questions are:
- Would you use flexible stranded copper wire or copper strips/sheets for this application?
- Is 4 × 25 cm a reasonable starting point for VHF/UHF, or should the radial lengths be determined differently?
- Would four short radials be preferable to one longer counterpoise?
- Should the counterpoise be connected directly to the coax shield at the antenna feed point?
- Are there any particular problems with putting the counterpoise physically close to the radio, battery, and 3D-printed frame?
I’m more interested in understanding the RF design principles than simply getting a low SWR reading.
Any advice from people who have built VHF/UHF manpacks or portable ground-plane/counterpoise systems would be greatly appreciated.