CB base antennas — Sirio
Sirio Thunder 27 no ground plane
Compact 25–29 MHz base antenna, loaded helical 1/4 λ dipole, 2.15 dBi, 100 W, SO-239
The Sirio Thunder 27 is a compact base station antenna for 25–29 MHz, designed to work without a ground plane. It is suitable for a balcony or a fixed installation with little space.
Key features
No radials
No ground plane required.
Compact
Loaded helical dipole.
5 MHz bandwidth
With SWR ≤ 2.
Specifications
| Type | Loaded 1/4 λ helical dipole |
| Frequency | 25–29 MHz |
| Impedance | 50 Ω |
| Radiation | Omnidirectional (360°) |
| Polarization | Linear vertical |
| Gain | 0 dBd · 2.15 dBi |
| Bandwidth | 5000 kHz (SWR ≤ 2) |
| SWR at resonance | ≤ 1.5 |
| Maximum power | 100 W CW continuous · 300 W CW for short periods |
| Feed | Direct, at the base |
| Connector | UHF female (SO-239) |
HamRadioShop | Base antennas
