17-FOOT VS. 25-FOOT
WHIP ANTENNAS

When you operate portable for Parks on the Air (POTA), camping or field days, a telescoping vertical antenna is one of the simplest and most versatile options. “Chameleon-style” here just means a telescoping whip you lengthen or shorten to change bands, mounted on a base with a few radial wires.

Whips in 17-foot and 25-foot lengths make band changes easy: extend or collapse the sections. But how far should you extend the whip for each band? This guide gives approximate starting lengths from 80 meters through 6 meters, plus practical advice for the field.

Understanding Antenna Length

A quarter-wave vertical is about one-quarter of a wavelength tall. You can estimate its length with:

Length in feet = 234 ÷ Frequency in MHz

This is a useful starting point for a simple, directly fed quarter-wave vertical with a suitable radial or counterpoise system. The real resonant length changes with antenna construction, radial layout, soil and nearby objects.

Approximate Vertical Antenna Tuning Chart

This chart applies to either a 17-foot or 25-foot telescoping whip when adjusted to the length shown.

* The 80-, 60- and 40-meter quarter-wave lengths are longer than both whip sizes. Those bands need a loading coil or matching arrangement, or a different antenna.

About 60 meters: it isn’t a full band like the others. In the U.S. it’s a narrow allocation near 5.3–5.4 MHz with its own rules, so check the current band plan before you transmit. The chart uses 5.357 MHz, a common operating frequency.

The 17-Foot Vertical Antenna

The 17-foot whip is an excellent portable choice, especially on 20 meters and up. At about 16.5 feet it’s near a quarter wavelength on 20 meters. Collapse sections to move to 17, 15, 12, 10 and 6 meters.

Recommended starting lengths:

• 20m — 16.5 feet
• 17m — 12.9 feet
• 15m — 11 feet
• 12m — 9.4 feet
• 10m — 8.2 feet
• 6m — 4.7 feet

For 30, 40, 60 or 80 meters you need extra loading or a suitable matching system, and performance depends on the whole antenna system.

The 25-Foot Vertical Antenna

The 25-foot whip adds flexibility, especially if you want 30 meters. At about 23.1 feet it approaches quarter-wave resonance on 30 meters without a loading coil in a typical installation, and it can still be shortened for the higher bands.

Recommended starting lengths:

• 30m — 23.1 feet
• 20m — 16.5 feet
• 17m — 12.9 feet
• 15m — 11 feet
• 12m — 9.4 feet
• 10m — 8.2 feet
• 6m — 4.7 feet

The longer whip is also handy for experimenting with a loaded 40 meters. But a longer whip doesn’t automatically mean better performance on every band.

Operating on 40, 60 and 80 Meters

A full quarter-wave vertical on 40 meters is about 32.5 feet, and 60 and 80 meters are longer still. Both whips are shorter than that, so the lower bands generally need loading coils, matching equipment or another antenna arrangement.

A well-designed loading system can make a shortened antenna resonant, but losses and lower radiation resistance reduce efficiency.

Operating on 6 Meters

The 6-meter band — the Magic Band — is exciting for portable operators. At about 50.1 MHz a quarter-wave vertical is only 4 feet 8 inches. Both whips can be shortened to about that length, if their sections collapse that far.

Because 6 meters is a high-frequency band, small length changes noticeably shift the resonant frequency. Check that the whip, mounting hardware and any matching parts are suitable for 50 MHz. With favorable propagation such as sporadic-E, six meters can deliver surprisingly long-distance contacts, and it’s good for local ones too.

Don’t Forget the Radials

For a conventional quarter-wave vertical, the radial or counterpoise system is extremely important. Radials give the return-current path and affect feedpoint impedance, ground losses and efficiency.

Portable operators often lay several wires on the ground connected to the antenna base. No single arrangement is best everywhere, and the number, length and placement of radials change the tuning. For repeatable results, use the same radial layout each time.

How to Tune Your Vertical in the Field

1. Select the band you intend to operate.
2. Extend or collapse the whip to the approximate length in the chart.
3. Install your radials or counterpoise.
4. Connect an antenna analyzer or SWR meter.
5. Check the resonant frequency and SWR.
6. If resonance is below your desired frequency, shorten the whip slightly.
7. If resonance is above your desired frequency, lengthen the whip slightly.
8. Repeat until the antenna is tuned for your operating frequency.

These steps apply to a simple resonant whip. If you use a loading coil, transformer or other matching network, follow the manufacturer’s instructions.

Why Your Results May Be Different

The numbers here are approximate. Tuning depends on:

• Ground conductivity and moisture
• Radial length and quantity
• Antenna mounting height
• Nearby trees, vehicles and metal structures
• Whip diameter and construction
• Feedline routing and common-mode currents
• Loading coils, transformers and matching networks

A whip that tunes perfectly at one park may need adjusting at the next. Some whips also can’t collapse to every length in the chart, so check the minimum and maximum usable lengths for your model.