You can improve mag-mount whip antenna’s performance by following three simple steps. Each step is independent of other and gives good improvement. All 3 together will be better, but first one (metal plate/food-can) is more important.
- Placing it over a metallic (preferably iron/steel) plate or food-can
- Un-screw the whip and use a thin copper or steel wire of length shown in photo below
- Try different location of antenna. Generally placing antenna near an outer window or outer wall improves reception.
Thin wire, such as wires of a scrap Network Cable RJ45, are suitable for making the DIY whip shown in above photos