DX Commander Signature 18 Nebula eXtreme HF Multi-Band Vertical Antennas

DX Commander Signature 18 Nebula eXtreme HF Multi-Band Vertical Antennas are an excellent choice for DX performance and general operations. Efficiently resonant on every HF band of operation, featuring wide SWR bandwidth and low take-off angle, the Signature 18 covers the Amateur bands 80 to 6 meters. DX Commander vertical antennas are based on the same principles as a fan dipole, with several vertical wire elements of various resonant lengths connected to a common feedpoint. The wire elements and support ropes are arranged with spacer plates around the non-conductive fiberglass mast. When installed with an appropriate radial system, the Signature 18 achieves efficient quarter-wave vertical performance with natural resonance and low SWR on every band, without the need for traps, coils or antenna tuners. Band-hopping DXing and simultaneous multi-band multiplexed operations are supported. The Signature 18 antenna is rated at 1500W SSB/CW, 400W FT8 and other digital modes.

This massive antenna is unrivalled by any other antenna on the market and stands at a massive 59 feet tall! The advantage of the eXtreme Nebula over the standard Classic or the Signature 12.4 is that the 80m element is fully vertical and top loaded via a small linear loaded section for fine tuning, giving you better night-time DX capability. Further, you also have the option of running 60m as a full quarter wave or the 20m element as a three quarter wavelength for improved gain. Because the antenna is almost resonant regardless of where you tune, the eXtreme Nebula is a fabulous shortwave antenna, achieving amazing listening results with broadcast, weather fax, RTTY, etc. across the spectrum.

The 12-section, thick-walled telescoping mast measures 59 ft. (18m) tall and weighs in at a hefty 13 lbs. (6kg). The base of the mast includes a larger DX Commander screw cap with screw threads large enough to accept the ground plate with ease. The top of the mast has a plastic loop that can be used to assist with fitting the 80m element before a foldback (optional).

Order your Signature 18 Nebula eXtreme HF Multi-Band Vertical Antennas from DX Engineering and get on the air!

NOTE: To achieve full extension of the mast, you will most likely require the help of an additional person to help to grasp and twist each section to achieve maximum heigh, it will require a strong twist and pull. This is a heavy system with thick-walled fiberglass. It is not necessary to achieve “full” height, the only element the full height helps with is the 80m band, which is tuned by folding the element back on itself.

This kit may NOT be suitable for a first-time kit-builder. Your appreciation for the scale and size needs to be fully understood. It is strongly advised that you complete a risk assessment before you start the build by calculating where this antenna will be installed so that in case of an accident, it will not damage property or cause injury to users or bystanders.

DX Commander Signature 18 Nebula eXtreme Features and Specifications

Alloy Plates: Aircraft-quality 5251 alloy, laser cut in England before deburring to give that “hammered” look, which eliminates sharp edges and provides a nice finish.

Spreader Plates: Marine-grade high-density polyethylene sheet material from USA, charcoal-gray, UV and environmentally stabilized to withstand the harshest of marine and high RF conditions. Spreader Plates are machine cut in England to DX Commander specifications.

Stay-Up Kit: Band style clamps, that keep the antenna mast sections extended, are molded in England in a black PA66 Nylon. Supplied in Hex or Wing Nut version depending on antenna model.

Shock-Cord: Marine grade shock-cord, with a UV and RF stable Dyneema woven exterior.

Spade Connectors: Kits include large spade connectors for best performance under tension.

Hardware: All nuts, bolts and washers are stainless steel.

Coaxial Connector: UHF female SO-239 coaxial connector, nickel plated brass with PTFE dielectric.

Fiberglass Poles: Made to DX Commander specifications in a spiral wound fiber, high-quality epoxy and paint finish.

DX10 Wire: Made in England for DX Commander, DX10 wire has an outstanding reputation for both strength and in particular, extreme flexibility. The insulation is “arctic grade” and still flexible down to -40° F. Originally designed for military use, this insulation is particularly strong but highly flexible and the stranded annealed copper wire is approximately 19 AWG and is made from 24 strands of 0.008 in. (0.2mm) wire.

SWR: The Signature 18 can deliver a curve with the 1.5:1 SWR points beyond most band edges, except 80m and 10m which has a 2:1 bandwidth of around 300kHz. On 40m, 30m, 20m, 17m, 15m and 12m, band edges are better than 1.5:1, with the best SWR typically at 1.1:1. Each band is adjustable to achieve the lowest SWR at either CW, FT8 or SSB frequencies.

NOTE: DX Commander antenna kits now include improved HCL EZ-Clamps and Dyneema Shock Cord instead of Carabiners.

* User assembly is required.

All DX Commander Signature 18 Nebula eXtreme Antenna kits come with everything you need (except for guying stakes):

• Signature 18 Telescopic Mast - 59 ft. (18m) Extended Height - Mast base - 2.87 in. (73mm)

• The DX Commander Ground Plate - 0.128 in. (3mm) thick laser cut 5251 alloy, with the mounting hole for the included SO239 assembly and 15 pre-tapped holes for ground radials. Use up to 4 radial wires per connector and you can double up on spade connectors to achieve a mind blowing 120 radials.

• The Driven Plate - 0.128 in. (3mm) thick laser cut 5251 alloy, laser cut with holes spacings to allow a selection of elements, as required. Choose 2 elements for say 80m and 60m. Perhaps a low-band special, say 80m, 60m and 40m. Perhaps an equidistant 4-hole pattern built into the template for folks who only want to run 4-elements, perhaps 80m, 40m, 30m and 20m. And finally, for those brave enough, run all six elements to give you the whole orchestra from 80m through to 6m.

• The kit comes with five 0.494 (10mm) thick plastic plates. The 4 lower plates are a massive 7.087 (180mm) in diameter. Each of the plates have a different hole pattern to fit snugly on the pole at just the right point. All the plates can be used as a guying point should the user want to protect their investment from severe weather. The fifth plate, near the top is 2.953 in. (75mm) in diameter and allows for a connection point for the 80m fold-over as well as the 60m spreader or 20m as a 5/8 element.

• 5 marine-grade high-density polyethylene Guy Plates and Spreader Plates

• 328 ft. (100m) 0.089 in. (2mm) Mastrant guying cable to allow builders to guy their antenna at three heights with a radius of 5m – 7m depending on area available.

• 3 - 328 ft. (100m) Spools of DX10 Antenna Wire

• SO-239 Coaxial Connector Assembly

• Selection of Spade Connectors

• HCL EZ-Clamps

• Marlow Marine Dyneema Shock-Cord

• Glue Lined Shrink-Wrap

• Stainless Steel Hardware

• Full HCL Stay Up Kit

• Guying and Shock-Cord - 32.80 ft. (10m) 550 Paracord

Signature 18 Nebula eXtreme FAQ

1. What is the gain improvement with the Nebula?

Improvement is on 80m, being almost full-sized – and the addition of 60m.

2. Why would one purchase the Nebula over the Multi-band 80m-6m HF Antenna or Signature 12.4?

Clean (not inverted L like the Classic or loaded like the Signature 12.4 ). Strong. Adds 60m.

3. Would the Nebula support 160m as an inverted L or with a loading coil at the base?

It would support 160m with very light-weight wire at around the 15m point, assuming that point was guyed too. Loading coils would destroy the other bands (experience)

4. Does the Nebula require two people to lower it to the ground?

Go slow and be careful. Safety is very important. DX Commander has experience of raising and lowering many masts. If in doubt, have a watcher to see what is happening behind you. As it comes down, there can be a lot of guy wire dropping around and you don’t want people tripping.

5. Which antenna would be better in high winds and heavy snow?

All of them. It so happens the original Classic has a reputation for holding up very well however like all these things, if you really do have a storm brewing, best to lower it. Interestingly, there’s one Classic that spent all winter under 6-feet of snow and it worked the whole time and came out the other side! The Signature series poles 9, 12.4 and 18m poles) are MUCH heavier than the Classic range. Most poles are known to have survived 80mph winds (dependent on wind gusts and other factors).