Antennas & feedlines
The antenna system usually matters more than the radio. It has to suit the band, the space you have, the mount, and the feed line — and a connector that screws on only proves mechanical fit.
Common antenna types
Starting points, not recommendations. Performance depends on height, surroundings, and the ground or counterpoise.
| Type | Typical use | What to check |
|---|---|---|
| Half-wave dipole | Single-band HF; the reference antenna for dBd | Length for the band, height above ground, center support, feed-line choke or balun |
| Fan / trap / multiband dipole | Several HF bands on one feed line | Element interaction, trap power rating, which bands actually match |
| End-fed half-wave (EFHW) | Portable and limited-space HF | Matching transformer power rating, counterpoise or coax length, common-mode current |
| Vertical (ground-mounted or elevated) | Low-angle HF, small footprint | Radial system — a vertical is only as good as its ground or radials |
| Mobile whip (NMO, magnet, lip mount) | VHF/UHF and HF mobile | Ground plane under the mount, bonding, cable route, weather sealing |
| Base collinear / J-pole | Local VHF/UHF FM and repeaters | Height and clearance, feed-line loss at UHF, lightning protection |
| Yagi / beam | Directional gain on HF, VHF/UHF weak signal, satellites | Rotator, mast and tower loads, polarization for the mode |
Gain changes the pattern
Gain is a comparison of radiation in a direction, not power created by the antenna.
dBi uses an isotropic reference; dBd uses a half-wave dipole. For the same direction and conditions, 0 dBd is approximately 2.15 dBi, so check which one a listing uses before comparing numbers.
More vertical gain means a flatter, narrower elevation pattern. That can help on flat ground and hurt in hills, near buildings, or when the other station is above you.
Feed-line loss needs a calculation
Frequency, cable type, length, and connectors determine the result.
Use the cable manufacturer's attenuation figure at the operating frequency, scale it to the actual run length, and add connector or adapter losses. The same cable loses far more at 440 MHz than at 7 MHz, so a run that is fine for HF can waste most of a UHF signal.
- High SWR on a lossy line adds more loss than the matched figure suggests.
- Larger low-loss cable helps long runs but needs matching connectors, bend radius, and strain relief.
- Use outdoor-rated cable, seal exterior connectors, and plan bonding and lightning protection at the entry point.
| Cable Type | Impedance & OD | Loss @ 10 MHz (HF) | Loss @ 50 MHz (6m) | Loss @ 146 MHz (2m) | Loss @ 440 MHz (70cm) | Best Application |
|---|---|---|---|---|---|---|
| RG-58 | 50 Ω · 0.195 in | 1.4 dB | 3.3 dB | 6.1 dB | 11.2 dB | Short patch cables, QRP portable field lines (< 25 ft). Highly lossy at UHF. |
| RG-8X (Mini-8) | 50 Ω · 0.242 in | 1.0 dB | 2.5 dB | 4.5 dB | 8.4 dB | Flexible mobile runs, portable HF operations, general shack jumpers. |
| LMR-240 | 50 Ω · 0.240 in | 0.8 dB | 1.8 dB | 3.0 dB | 5.3 dB | Double-shielded low loss for vehicle VHF/UHF installs and portable setups. |
| LMR-400 | 50 Ω · 0.405 in | 0.4 dB | 0.9 dB | 1.5 dB | 2.7 dB | Standard base station feedline for long runs to towers, beams, and VHF/UHF antennas. |
| 450 Ω Ladder Line | 450 Ω window line | < 0.1 dB | 0.2 dB | 0.4 dB | 0.9 dB | Balanced multi-band HF center-fed doublets tuned with an antenna tuner. Negligible SWR loss. |
Loss figures are approximate dB per 100 feet (30.5 meters) into a matched 50-ohm load at 68°F (20°C). In this table the loss at 440 MHz is roughly 7 to 9 times the 10 MHz figure.
What Part 97 says about antennas
Short, and mostly about structures and safety.
- Structures more than 200 feet (60.96 m) above ground, or near a public-use airport, must be notified to the FAA and registered with the FCC under Part 17 (§97.15(a)).
- State and local regulation must reasonably accommodate amateur communications and be the minimum practicable regulation — the PRB-1 rule (§97.15(b)). It does not override private covenants or HOA rules.
- Antenna Gain vs. Power Ceilings: On bands governed by peak envelope power (§ 97.313(b)), transmitter power is measured at the output terminals into the feedline—antenna gain does not count against your 1,500 W or 200 W PEP limit. In contrast, on 60 m (§ 97.313(i), 100 W ERP on the channels and 9.15 W ERP in the segment), 630 m (§ 97.313(l), 5 W EIRP) and 2,200 m (§ 97.313(k), 1 W EIRP), power is capped as radiated field strength, requiring antenna gain to be deducted from transmitter wattage.
- Before transmitting, the licensee must make sure the station meets the FCC RF exposure rules (§97.13(c)). Antenna height, distance from people, power, and duty cycle all feed that evaluation.
Antenna construction notes, field deployments, and measurement write-ups are documented in the journal.