Nebula xTreme DX Commander 18m Antenna Kit

Nebula xTreme DX Commander 18m Antenna Kit

Building on the success of the original DX Commander Classic, I am proud to launch the 18m eXtreme which delivers all HF bands from 80m through 6m (and 4m) in a vertical package with a price/performance curve, unrivalled by any other antenna on the market that will achieve more DX, great reception and instant band-hopping.

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For 2 x VFO radios, you can use this same antenna on two bands at the same time, tuned and ready. There are no control wires, no moving parts – and no circuitry to go wrong.

The eXtreme Nebula kit is shipped in two boxes, 1) the very large eXtreme DXC telescopic pole, which extends to around 17.5m in length and 2) the kit of parts. Worldwide shipping.

18m Telescopic Pole

Weighing in at a hefty 6kg, this 12-section telescopic thick-walled pole is genuinely a monster. The base has the customary DX Commander screw cap, albeit MUCH bigger than the 10m Classic. The screw threads are large enough to easily accept the ground plate with ease. Base of the pole is 73mm. The top of the pole has an optional plastic loop (in the box) which users may use to attach the 80m element through. Glue not provided but any super-glue will work.

Conversion kit

The box of components includes the following:

The DX Commander Ground Plate in 3mm thick laser cut 5251 alloy, with the SO239 tab machine bent to 90 degrees and 15 holes, pre-tapped for ground lugs. Use up to 8 radial wires per fork connector and you could even double up on fork connectors to deliver a mind blowing 240 radials.

The Driven Plate, again in 3mm 5251 alloy, laser cut with holes spacings to allow a selection of elements, as required. Choose 2 elements for say 80m and 60m. Choose a triangular pattern for a low-band special, say 80m, 60m and 40m. Perhaps an equidistant 4-hole pattern in-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.

ground arrangement

The kit comes with five x 10mm thick natural UHMWPE plates. The 4 main plates are a massive 180mm in diameter. Each of the plates have different hole sizes to fit snugly on the pole at just the right point and all plates can be used as guying points, should the user want to protect their investment from even the stormiest of weather. The fifth plate, near the top is 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.

400m (1,300 feet) arctic-grade DX10 is included in the kit in four reels of 100m. This antenna wire works well as both elements and radials. Made in the UK for DX Commander, DX10 is made from 24 strands of pure copper 0.2mm wire, with a reputation for accepting 1,500W key down (tested for 65 seconds at 1,600W).

100m 2mm Mastrant guying cable is also included in the kit to allow builders to guy their antenna at three heights with a radius of 5m. Guy stakes need to be sourced locally.

The stay up kit is delivered in the form of 12 x stainless hose-clamps and 10mm ID neoprene rubber tubing which is UV stable. The hose clamps start at 70mm and reduce in size to the smallest.

22 stainless nuts, washers and wing nuts together with a large selection of fork connectors are also included. These are the same as used on the DXC Classic along with 1m length of double-walled, glue-lined heat shrink to protect element ends, fork connectors and the various mechanical loops to keep your elements taut.

Further, we are including 4m of Marlow marine shock-cord and professional shock-cord end-clasps. These attach your elements to the various spreaders.

BANDS

The advantage of the eXtreme Nebula over the standard classic is that your 80m element is fully vertical, not an inverted L giving you better DX capability. Further, you also have the option of running 60m as a quarter wave too or a 20m element as a 58th.

It should be noted that the 80m element will also give you a perfect tune on the 11m and the 10m bands as a 1 and ¾ wave. There is extremely useful gain on these bands, achieving 6dB better DX gain (5 to 10 degrees above horizon) over a quarter wave.

With 4-elements still to go, I recommend you fit 40m as a quarter wave in the same configuration as the Classic. That means cutting your element long and folding back the top which allows for a slightly linear loaded 15m element too.

The fourth mandatory element, in my opinion, would be a 20m quarter wave. Alternatively, I have tested this as a 20m 5/8th using the “foldback” (as 40m and 15m) method however SWR was not better then 1.6:1. For a tube amplifier or users with ATU buttons on their radio, go for it. If you want to run flat SWR curves, cut a quarter wave element here instead. There is very little difference in reality, it would just be very cool run a 5/8th on 20m.

That leaves two elements to populate the Driven Plate:

17m band is nearly catered for by the 80m element, delivering almost a 5/8th here however you will probably find the SWR is a little higher than ideal at around 2.5:1 because the resonance is about 500kHz above the band. You would need a dedicated quarter wave to run flat SWR curves alternatively, you could dispense with that and use the ATU function on your radio. For transistor amplifier QRO users unless you are comfortable with an outboard ATU, you would be better off with a dedicated quarter wave here.

Assuming you now have 80m, 60m, 40m, 20m, 15m and 11m/10m covered your last option is the 6th element. 30m band is obviously a fantastic CW and FT8 band and would be my choice – else the only “gap” you have is 12m. It should be noted that SWR on 12m is not too bad, around 2.5:1. My recommendation would be to cut your 12m losses and go down the 30m route.

Finally, bonus bands. 40m element will give you a perfect tune at around 50.150 and 30m element will give you another SWR curve-dip for the your FM portions of the 6m band.

For 4m band (70MHz) users, again that is also resonant with useful gain reported by users of the Classic.

Even 2m band is resonant(!). There are various videos on YouTube of folks opening repeaters 30-miles away using their HF Classic. I have never tested 70cms.

SHORTWAVE LISTENING

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. Enjoy!

I am releasing 40 kits for dispatch at end October 2020 at a special introductory price of £465. It is likely the next batch will have to have a price increase.

As I type this, I have not written the user guide. Be assured, you will get a cut-chart and full user-guide with your order.

PHOTOGRAPHS

The photos in this gallery have only three (3) UHMWPE plates. This was my prototype. The production system will have 5 plates with ideal guying positions shown in the graphic.

I used a home-brew tilt-over mast base which was fun to build. However, it is quite feasible to do this without. The procedure will be detailed in the user guide.

NOTE: To achieve full extension of the pole, you will most likely require the help of an additional person to grasp and twist each section with you to achieve maximum height overall. It will require a strong pull. This is a heavy systemwith thick-walled fiberglass.

Note #2: The 18m poles are currently NOT available individually due to low stock levels. These will be on-sale early next year (2021).

DISCLAIMER: This kit is probably NOT suitable for a first-time kit-builder. Your appreciation of the scale and size needs to be fully understood. I advise strongly that you make a risk assesment before you start the build by calculating where on your land this will sit – and further that in case of any accident, it will not damage property or cause injury to bystanders or users alike.

DELIVERY:

  • All International and EU deliveries will utilise FedEx at £95 (for both boxes).
  • For UK deliveries, I will be using ParcelForce at £55.
Price: £565.00£465.00
 
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