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Projects Portable antenna selection

Antennas / Decision Researched

One antenna, every band,
without touching it

The requirement was narrow and worth stating plainly: erect one portable antenna once, then change bands from the radio. No moving coil clips, no adjusting whip lengths, no opening links, no putting up a different antenna for every frequency. Budget $375, feeding an Icom IC-706MkII at up to 100 W SSB on HF.

Radio
Icom IC-706MkII
Budget
$375 maximum
Power
Up to 100 W SSB, ~50 W for some work
Wanted
Regional NVIS and long-haul DX
Band change
Electronic, from the radio
Use
POTA, field, emergency

Why this is hard

The central problem

NVIS and DX want opposite geometry. A low horizontal radiator produces predominantly high-angle radiation, which is what regional coverage wants. A vertical, a high sloper, or anything with a substantial vertical component produces more low-angle radiation, which is what reaches distance.

RADIATION ANGLE, NVIS AGAINST DX ELEVATION PATTERNS PLOTTED K4DIA REF 0 dB AT OUTER RING TYPE ILLUSTRATIVE -3 -6 -10 0 30 60 90 120 150 180 NVIS ELEVATION ANGLE, DEGREES A low horizontal radiator. Energy leaves near the vertical and returns close in. -3 -6 -10 0 30 60 90 120 150 180 DX ELEVATION ANGLE, DEGREES A vertical, a sloper, or a strong vertical component. Energy leaves at a low angle and travels. PLOT NOTES: 1. Pattern shapes are drawn to compare geometry. They are not modelled results and carry no gain figures. 2. Rings are relative, 0 dB at the outer circle down to -20 dB at the centre. Ground is at 0 and 180 degrees. 3. No single fixed portable antenna is optimal for both cases at once.
No fixed portable antenna is optimal for both at once. What works is a single inverted-L or sloping wire that produces a mixture of angles, or a modular system whose geometry changes when the mission changes rather than when the frequency does.
Note

A tuner changes the impedance presented to the transmitter. It does not make an electrically short antenna efficient, it does not replace missing radiator length, and it does not guarantee a useful radiation pattern. A low SWR reading is not proof of good radiation.

Four candidates

What was considered

Published figures
Sources at the foot

Buddipole

Conflicts with the requirement

A manually adjusted loaded dipole and vertical system. Genuinely good at what it does, which is not this.

Published

  • 7 to 54 MHz continuous, plus 144 to 148 MHz
  • 40 through 6 m, plus 2 m
  • About 16 ft extended, about 22 in packed
  • QRP through 250 W
  • About $279 basic, about $459 deluxe

For

  • Highly modular, compact packed
  • Dipole, asymmetric dipole or vertical
  • Includes 2 m
  • No DC power, no radio-specific interface
  • The basic antenna stays within budget if a suitable support is already to hand

Against

  • Band changes mean moving clips and adjusting whips
  • An analyzer is strongly recommended for repeatable setup
  • Standard coverage starts at 40 m
  • 80 m needs optional low-band parts and is compromised
  • Deluxe package is over budget

Icom AH-4

Closest fit

A weather-resistant automatic tuner made to live at the antenna feedpoint, controlled natively by the 706.

Published

  • 3.5 to 54 MHz with a wire at least 7 m / 23 ft
  • 7 to 54 MHz with the optional AH-2b whip
  • 120 W PEP maximum input, 50 ohm input impedance
  • Tunes in about 2 to 3 s, 15 s worst case
  • 45 memories
  • 13.8 VDC, under 1 A
  • 6.77 x 2.80 x 9.06 in, about 2.65 lb

For

  • Native control from the 706 tuner connector
  • Hold the radio's TUNER button and it goes
  • Mounted at the feedpoint, minimising loss in a mismatched coaxial feed line
  • Takes a long wire directly
  • Made to sit outdoors

Against

  • No official 160 m
  • No 2 m
  • Needs coax plus the Icom four-conductor control cable
  • Control cable run limited to about 10 m / 32.8 ft, using the proper shielded extension and matching coax
  • It is a tuner: wire, counterpoise, support and cable still needed

LDG AT-200ProII

Best tuner, wrong place

A general purpose automatic desk or go-box tuner that sits beside the radio and feeds a coax-fed antenna.

Published

  • 1.8 to 54 MHz
  • 250 W SSB, 200 W CW, 150 W FT8, 125 W other digital, 100 W on 6 m
  • About 6 to 1,000 ohms, to 4,000 with the optional 4:1 balun
  • Two antenna outputs, 4,000 memories total, 2,000 for each output
  • 0.2 to 15 s full tune, about 0.2 s from memory
  • 9.5 x 7 x 2.25 in, about 2.5 lb, 11 to 16 VDC at up to 1 A

For

  • Official 160 through 6 m
  • Higher power and digital ratings than the AH-4
  • Two switchable antenna outputs
  • Forward, reflected and SWR displays
  • The optional IC-PAC cable connects to an Icom AH-3 or AH-4 compatible tuner port, supplies control and DC, and LDG lists the IC-706 as supported

Against

  • Not weather resistant
  • Lives beside the radio, not at the feedpoint
  • Feeding a highly mismatched antenna through coax, it protects the transmitter while the coax still sees high SWR and the extra loss
  • Includes no antenna
  • Random wire and open line need external matching hardware

LDG RT/RC-100

If 160 m matters

LDG's answer to the AH-4: a remote tuner at the feedpoint, powered and controlled over the coax itself.

Published

  • 1.8 to 54 MHz
  • 125 W SSB peak, 100 W CW, 75 W FT8, 50 W other digital, 50 W on 6 m
  • About 4 to 800 ohms, to 3,200 with the optional 4:1 balun
  • Over 2,000 memories
  • RT-100 about 1.25 lb, weather resistant but not immersible
  • About $299.99 observed

For

  • Feedpoint mounting keeps the loss off the coax
  • Official 160 through 6 m
  • No outdoor control cable: power and control ride the coax
  • Brand agnostic
  • Fits within the budget when combined with inexpensive wire and hardware

Against

  • Long wire or balanced feed may need an external balun or unun
  • No native AH-4 style control through the 706 tuner port
  • Lower digital power limits than the AT-200ProII
  • Still no 2 m
  • A short radiator stays inefficient on 160 m however good the match

Side by side

The decision table

RequirementBuddipoleIcom AH-4LDG AT-200ProIILDG RT/RC-100
Within $375 as offered or usedYesYesYesYes, about $300 new
Includes a radiatorYesNoNoNo
No physical adjustment between HF bandsNoYesWith a suitable antennaWith a suitable antenna
Remote feedpoint tuningNoYesStation sideYes
Native IC-706 controlNoYesWith IC-PACUses the RC-100 controller
160 m tuner coverageNoNoYesYes
80 m coverageOptional, compromisedYes, with 23 ft or more of wireYesYes
6 m coverageYesYesYesYes
2 m coverageYesNoNoNo
Weather resistantThe antenna itselfYesNoYes
Best roleCompact adjustable antenna706 remote wire couplerShack and go-box tunerUniversal remote tuner

The antenna itself

One wire, put up once

For either the AH-4 or the RT/RC-100: a single 55 to 70 ft wire as an inverted-L. Up the mast first, then out. Remote tuner at the bottom, counterpoise on the ground, and the far end kept away from anywhere a person can reach it.

ONE WIRE INVERTED L ELEVATION, 80 TO 6 M DRAWN K4DIA SCALE NONE REV A SHEET 1 OF 1 23 TO 30 FT 30 TO 40 FT, LEVEL OR SLOPING DOWN 55 TO 70 FT OF WIRE IN TOTAL TUNER COAX RADIO 1 2 3 ITEM DESCRIPTION 1 End insulator. Keep this end clear of people and paths. 2 Counterpoise, 50 to 100 ft of wire on or just above the ground. 3 Remote tuner at the feedpoint. NOTES: 1. Erected once. Bands are changed electronically at the radio. 2. Lengths are the recommended range, not a cut list.
Erected once, then retuned electronically when the band changes. That is the whole point of the arrangement.

What to expect from it, band by band

80 m
The horizontal part gives high-angle regional coverage, the vertical part contributes some lower angle.
40 m
A useful mixture of regional and longer haul.
30 to 10 m
An increasingly complicated multi-lobe pattern, still useful portable.
6 m
It may tune, but a dedicated 6 m radiator gives a more predictable pattern.
160 m
An LDG tuner may match 55 to 70 ft of wire, but it stays electrically short and inefficient. More wire and a better return path help materially.

This is a compromise antenna. It will not equal a low full-size NVIS dipole and a full-size quarter-wave DX vertical at the same time. What it buys is operational agility.

How each one is actually wired up

Practical configurations

AH-4, for 80 through 6 m

The recommended arrangement.

  1. Icom AH-4 at the antenna.
  2. 55 to 70 ft insulated radiator wire.
  3. 23 to 30 ft fiberglass support, or a suitable tree.
  4. Counterpoise totalling about 50 to 100 ft.
  5. 50 ohm coax back to the radio.
  6. Icom four-conductor shielded control cable to the TUNER socket.
  7. Change frequency, hold TUNER, transmit once it tunes.

AT-200ProII, as a go-box tuner

Bigger footprint, more capability.

  1. About an 88 ft non-resonant doublet: two 44 ft legs.
  2. Parallel transmission line from the center.
  3. External 4:1 balun at the tuner.
  4. AT-200ProII beside the radio.
  5. Optional LDG IC-PAC cable to the 706.
  6. Once up, it stays up while the tuner retunes electronically.

RT/RC-100, when 160 m matters

One coax does everything.

  1. RT-100 at the feedpoint.
  2. RC-100 controller and bias tee beside the radio.
  3. One coax carries RF, DC and control.
  4. External balun or unun chosen for the documented configuration.
  5. The longest practical inverted-L or sloping wire, over 70 ft if 160 m is the goal.

The band none of them cover

Two meters

Neither the AH-4 nor either LDG tuner covers 2 m. The Buddipole can be configured for it, but that means changing its arrangement, which is the thing this whole exercise was trying to avoid.

The 706 has a separate VHF/UHF antenna port, so the least disruptive answer is a small dedicated 2 m antenna left permanently connected: a roll-up J-pole, a quarter-wave whip, or a small magnetic mount.

Asking one radiator to cover 1.8 MHz through 148 MHz efficiently is a frequency ratio above 80 to 1. A separate compact VHF antenna is the better answer technically and operationally.

The answer

Recommendation

In order
For the stated requirement

  1. 01

    Icom AH-4

    For 80 through 6 m and the strongest integration with the 706. One 55 to 70 ft inverted-L. Tunes at the feedpoint, weather resistant, no physical adjustment when the band changes.

  2. 02

    LDG RT/RC-100

    If official 160 m tuner coverage matters. Longest practical inverted-L or sloping wire with the right external matching, and the remote feedpoint placement, still inside budget.

  3. 03

    LDG AT-200ProII

    If a versatile indoor or go-box tuner is also wanted. Most tuner power, the displays, two antenna outputs, official 160 through 6 m. Pair it with a deliberately chosen broadband antenna.

  4. 04

    Buddipole

    Only if compact mechanical modularity and native 2 m outweigh automatic band changes. A capable antenna that needs the most physical fiddling as the band moves.

Before you transmit

Operating notes

  • Start tuning and testing at reduced power.
  • Do not transmit while anyone can touch the radiator, the counterpoise, the tuner output, or the wire ends.
  • High RF voltage exists at the far end of an end-fed or inverted-L wire.
  • Keep antennas and supports well away from overhead electrical conductors.
  • Check current FCC band privileges and RF exposure requirements for where you are operating.
  • Observe the maker's mode-specific power limits, especially for FT8 and other high duty cycle digital modes.
  • A low SWR match does not prove good radiation efficiency.

Prices and availability change. Confirm the included cables, accessories, condition and return policy before buying new or used. Figures above are the published ones as found during research, not measurements.

Sources