Elecraft AX1 antenna

| octubre 3, 2018

Elecraft AX1 antenna

The Elecraft AX1 is a compact telescoping whip that disassembles into two 6” (15 cm) pieces, so it’ll fit into small “grab & go” bags… or your back pocket. A two-position switch selects 20 m (resonant) or 17/15 m (compatible with a low-loss match via an antenna tuner on both bands).

The AX1 is ideal for pedestrian mobile, “stealth” operation, or whenever dipoles, verticals, long wires, and other full-size antennas cannot be erected. It can be used in three ways:

  • HT-style (shown here with an Elecraft KX2 all-mode, 8010 meter transceiver)
  • On a table-top with a right-angle BNC adapter and an AXB1 whip bipod
  • Mounted on a tripod or other support using an AXT1 tripod adapter
Elecraft AX1 antennaFOR BEST RESULTS, USE THE AX1 WITH AN ATU

(automatic antenna tuner). The ATU will handle variations in terrain, radial length, height, body capacitance, etc.

All Elecraft transceivers have optional wide-range internal ATUs that are fully compatible with the AX1. An external ATU such an Elecraft T1 may also be used.

Caution
  • The AX1 is not intended for vehicle-mounted use or for permanent outdoor installations.
  • To avoid damage to the telescoping whip, keep it collapsed when not in use.
  • Always use at least one radial (included). This improves transmit signal radiation by up to 20 dB, and reduces the risk of getting an RF burn from the mic, key, or chassis at higher power levels.

NOTE: All BNC plugs have some “play.” It’s normal for the whip to tilt slightly when attached directly to a transceiver.

Elecraft AX1 Specifications

Resonant

Frequencies

20 m (~14 MHz) and 17/15 m (~19 MHz). Resonant frequencies may vary +/- 300 kHz or more due to variations in terrain, antenna height, body capacitance, and length of radial(s).
Supplied Radial Wire 13 feet (3.3 m) long. Wire has preinstalled lug for transceiver attachment.
Max. Power 30 Watts. If RFI symptoms are observed, reduce power or move antenna farther from the transceiver.
Construction Corrosion-resistant whip and hardware; Lexan outer tube; high-Q inductors using #20 AWG high-temp enamel wire.
Dimensions Whip: 6” (15 cm) collapsed, 45” (115 cm) extended. Base: 6” (15 cm) x 0.75” (19 mm) dia.
Weight 3.8 oz. (107 g) including supplied counterpoise wire.

Elecraft AX1 antennaElecraft AX1 Setup

  • Thread the whip into the base, then fully extend it.
  • Plug the AX1 into your transceiver’s BNC jack for HT-style operation. For right-angle use with an AXB1. For use with a camera tripod and an AXT1.
  • Select the 20 or 17 m switch position on the AX1 as shown at left. Use the 17 m position for 15 m. (An ATU is always required for 17 and 15 m use.)

ATTACH AT LEAST ONE COUNTERPOISE WIRE (or radial) to your transceiver’s ground screw. Otherwise, your transmit signal will be as much as 20 dB weaker (4 to 5 S-units). A 13’ (3.3 m) insulated wire with a solder lug at one end is supplied with the AX1. When using a KX2 or KX3, secure the solder lug to the rig at the thumb screw closest to the antenna jack. (An option for the KX2 is to use a mini-banana plug, e.g. Elecraft KX2GNDPLUG, with the quick-release ground jack on the left side panel.)

  • Match the antenna to the transceiver using an ATU or with manual length adjustments as described below.

Using an ATU

The resonant frequency of any short whip can be affected by many factors. Pedestrian mobile operation complicates the issue because of changes in terrain and in the location of the radio relative to the operator. An ATU can compensate, eliminating tedious whip or radial length adjustments.

To match using an ATU: Tap the ATU tuning switch on the radio or tuner. If you’re using a K3S / K3 / KX3 / KX2, tapping the tune switch a second time may result in a better match.

Manual Adjustment

Non-ATU operation is possible on 20 meters where the AX1 is near resonance.

To adjust antenna length manually: Check the SWR at both the low and high end of the desired band. If SWR is higher at the low end of the band, lengthen the radial. If SWR is higher at the high end of the band, shorten the radial or reduce the length of the telescoping whip.

NOTE: In cases where it is difficult to achieve a low SWR (< 3:1), transmitting may still be possible at reduced power. Elecraft transceivers can be safely used at high SWR.

Operating Tips

•    At QRP power levels, CW and certain data modes (including FT8) will have an advantage over SSB.

•    To improve signal strength, elevate the AX1 above ground by standing or using a tripod. When operating outdoors, seek high ground, or an area with a downslope in a preferred direction. Such a slope may act as a reflector. Indoors, extend the telescoping whip outside a window if at all possible, and allow the counterpoise wire to hang outside the window as well. Use a balcony if available.

•    When operating pedestrian mobile (/PM), let the counterpoise wire trail out behind you. As terrain changes, SWR may fluctuate during transmit. An ATU, if available, can compensate; tap the ATU tune button if SWR is high.

•    Try operating during contests when there’s lots of activity (most weekends). Contest stations often have high-gain antennas, benefitting both ends of a QSO.

•    Rather than call CQ, try answering strong stations who are calling CQ or just completing a contact. A strong signal is often an indication that propagation is excellent in that direction.

•    Tune slowly, especially when listening for weak signals.

As an example, SOTA (Summits On The Air) portable stations can often be found between 14058 and 14063 kHz, but they may be very weak.

QRP operation with a short whip can be both rewarding and challenging.

For times when conditions are poor, we recommend also carrying a lightweight wire antenna. A simple random-length antenna can be made from two 25’ (7.5 m) lengths of #26 “Silky” (thewireman.com). Toss one wire into a tree and lay the other on the ground, or into a second tree. Attach the wires to the transceiver via a BNC-to-binding post adapter, such as our model BNC-BP. Elecraft ATUs will usually match this efficient antenna on 40 through 10 m.

Elecraft AX1 antennaAXB1 Whip Bipod

A whip antenna used with a right-angle BNC may tip over due to wind load. To stabilize a whip in light to moderate winds, an AXB1 bipod can be used as described below.

 

To use the AXB1:


•    Attach a right-angle BNC adapter (Elecraft BNC-RA or equivalent) to the antenna.

•    Snap the AXB1’s plastic clip firmly onto the knurled part of the AX1’s BNC connector as shown by the upper arrow at left.

Caution: To detach the plastic clip from the antenna, do not snap it back off, as this can stress the connector. Instead, slide the connector back through the clip by pushing firmly on the BNC adapter where indicated by the lower arrow.

•    Adjust AXB1 leg angle and height as needed.

•    In strong winds, orient the rig so the antenna is facing into the wind, or strap the AXB1 to the surface. Holes are provided in the legs.

•    Firmly tighten the AXB1’s thumb screw.

   For storage or transport, fold the legs of the AXB1 together. An AX1, AXB1 and KX2 will all fit in an Elecraft CS40 or ES40 bag.

NOTE: The legs of the AXB1 may not be in electrical contact with the whip’s BNC connector, so they should not be used as a radial wire attachment point.

 

Elecraft AX1 antennaAXT1 Tripod Adapter

Elevating a whip antenna using a tripod may improve effectiveness on both transmit and receive. An AXT 1 adapter will work with most camera tripods having a 1/4-20 threaded mount. Any lightweight whip with a BNC connector may be used.

To use the AXT1:

•    Secure the AXT 1 to the tripod’s threaded mount as shown below.

•    Attach the AX1 (or other BNC-base whip) to one of the adapter’s BNC connectors.

•    Attach a length of 50-ohm coax to the adapter’s other BNC connector. Use a short, high-quality cable to minimize loss. An ATU or manual antenna length adjustments may be required.

•    Attach at least one counterpoise wire to either the transceiver, as described on page 3, or directly to the AXTTs aluminum bracket. Holes are provided for this purpose. (Transmit efficiency may be improved by using two or more counterpoise wires.)

•    Bracket holes can also be used for guying, or with other attachment hardware (user-supplied).

(Tripod not included.)

Counterpoise Wires

The counterpoise (or radial) wire supplied with the AX1 is usable on all three covered bands (20, 17, and 15 meters). The two inductors in the base unit have been adjusted to provide resonance close to the 20 meter band with this radial length. Adding more radials may yield improved results on one or more bands.

During pedestrian-mobile operation, a single “dragged counterpoise” wire is typically used to minimize the risk of snagging or other hazards. Optimal length for a dragged counterpoise varies with many factors, but the length most often used is:

L (ft) = 185 / F, or L (m) = 56 / F (F in MHz).

A good starting point for elevated radials (e.g., using the AX1 with a tall tripod or mast) is a full quarter wavelength:

L (ft) = 234 / F, or L (m) = 71.3 / F.

Radial length adjustments to achieve resonance can be tedious. An antenna analyzer is recommended.

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