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Nebula xTreme DX Commander 18m Antenna Kit
See Unified user guide here: https://www.m0mcx.co.uk/dx-commander-user-guides/
Building on the success of the original DX Commander Classic, we have launched the giant 18m eXtreme which delivers all HF bands from 80m through 6m (and 4m as it happens) in a vertical package with a price/performance curve, unrivalled by any other antenna on the market that will achieve fast and instant band-hopping.
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 world-wide 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.
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 accept the ground plate with ease. Base of the pole is 73mm. The top of the pole has a plastic loop to attach the 80m element.
Conversion kit
The box of components includes the following:
The DX Commander Ground Plate in 3mm thick laser cut 5251 alloy, with the hole for SO239 assembly (supplied) 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 up to 240 radials.
Stay Up Kit is via our new PA66 Nylon Clamps with 8mm Hex Clamps.
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. Perhaps 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.
The kit comes with five x 10mm thick natural UHMWPE plates. The 4 main plates are a massive 180mm in diameter and thick too. Each of the plates have different hole patterns to fit snugly on the pole at just the right point. All the 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.
100m arctic-grade DX10 is included in the kit and a further TWO reels of Tri-Rated Radial Wire..
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 on 14MHz).
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 stainless clamps and clear PVC tubing.
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 a long length of upgraded Marlow marine shock-cord. These attach your elements to the various spreaders (via the shock cord).
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 5/8 (actually a 3/4 wave).
It should be noted that depending on how the linear loading is arranged, you can achieve a perfect tune on the 11m and the 10m bands too (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, we 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 delivering around 2-3dB of extra gain.
The fourth mandatory element, would be a 20m quarter wave. Alternatively, we 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 (although with a very good ground, the difference between the two is probably negligable).
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.
For 4m band (70MHz) users, again that is also resonant with useful gain reported by users of the Classic.
Even 2m band is normally 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.
PHOTOGRAPHS
The photos in this gallery have only three (3) UHMWPE plates. This was my prototype. The production system has 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. See note below.
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 system with thick-walled fiberglass.
FAQ
1. What is the gain improvement with the Nebula?
Nothing apart from 80m really. And in that case, possibly 2-3dB. And of course, addition of 60m.
2. Why would one purchase the Nebula over the Multi-band 80m-6m HF Antenna?
Bragging rights! 🙂 Clean (not inverted L like the Classic). Strong.
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. Loading coils would cock-up the other bands (experience)
4. Does the Nebula require two people to lower it to the ground?
I did everything myself – but I have experience of raising and lowering many masts in my time. I would say one person is safe. 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 up.
5. Is there a video we can view showing the raising/lowering of the Nebula?
Previous videos were not very good. We will do another one soon.
6. 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 take it down. 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 (9.5, 12.4 and 18m poles) are MUCH heavier than the Classic range.
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.
NOTE: Tested at 1,600W key-down for 65 seconds on 14MHz
SHIPPING:
Note, this is a LONG pole which means shipping is a little more than we would like.