Two Antennas from Moonraker
PW editor Don G3XTT tries out two versatile antennas from Moonraker.
Antennas are an endless source of fascination and experimentation for radio amateurs and I am not one to turn down an opportunity to try out some alternatives, especially as I no longer have my tower and multiband beam.
So, I was more than happy when Chris Taylor of Moonraker offered me not one but two antennas for review. Both are sold as multiband wire antennas suitable for both home and portable use. One is a well proven design dating, believe it or not, from 1936, while the other is an amateur radio version of what is described as a ‘civilian military systems’ antenna.
The W3EDP
Let’s start with the familiar one, the socalled W3EDP antenna. The first description of it appeared in the ARRL publication QST of March 1936 in the Experimenter section under the title An Unorthodox Antenna. It was written by Yardley Beers W3AWH about the experiments that his friend HJ Seigel W3EDP had undertaken.
The W3EDP antenna is a development of the early Zeppelin or Zepp antennas that were used before the Second World War. They obtained their name from the fact that end-fed wires were required for use on Zeppelin airships.
The original W3EDP configuration is shown in Fig. 1. The antenna was designed for the then amateur bands of 160, 80, 40, 20 and 10m. There was, of course, no software available to W3EDP to design the antenna so the design was very much a case of ‘cut and see’. And it would feed directly from the pi-tank of a valve transmitter, which was able to handle a wide range of impedances.
Although the 84ft radiating element remained the same for all bands, W3EDP found that the 17ft counterpoise worked well on most bands while on 20m, a length of 6½ft seemed to work best.
The modern take on the W3EDP antenna, designed to work with the current crop of solid-state transmitters, is shown in Fig. 2. It’s sufficiently different that it probably shouldn’t be described as a W3EDP antenna at all, but it retains this designation in all the literature.
In essence, the W3EDP is simply an endfed wire antenna, with the length chosen as a suitable compromise for the various bands and, in the modern version, with the twin-wire feeder and balun or more accurately a Unun (unbalanced to unbalanced transformer) acting to transform the what would otherwise be a high end impedance to something that the rig can handle (albeit, through an ATU).
The Moonraker W3EDP
Which takes us nicely to the W3EDP as sold by Moonraker. The photo, Fig. 3, shows what arrives: a 67ft length of Flexweave wire for the top (horizontal) section, a 17ft length of 300Ω twin-feeder (air spaced) for the vertical part and a 4:1 balun to match to the coaxial feeder. The antenna is rated for 400W.
The description on the Moonraker website is fairly sparse - Works well on 80m and 40m, Length: 67ft, Requires ATU. On the paperwork that comes with the antenna, there is a little more: 80-10m with a good quality
ATU, the ribbon feeder must be hung in free space or mounted on a non-metallic mast, ideal for the smaller garden and great for portable operations.
In my case, I put up two 20ft fibreglass poles to support the antenna. This leaves the balun a convenient couple of feet above ground, which makes it very simple to connect the feeder.
The problem with any compromise antenna (and using a single length of wire on several bands is bound to lead to compromise, albeit it makes for a simple all-band solution) is that the impedance at the feedpoint will vary from band to band. This means that the feeder will not be seeing 50Ω and will act as a transformer, the transformation between feedpoint and shack end depending on the length of feeder. Hence the need for an ATU (ideally, the ATU
would be at the feedpoint but that’s inconvenient for most situations, unless you have a remotely-controlled ATU). To illustrate the impact of this, Fig. 4 shows a plot of SWR as measured at the base of the antenna and Fig. 5 the same frequency range as measured in my shack at the end of maybe 50ft or so of coax. So, it doesn’t really make sense to show a table of SWR – it depends on how long your feeder run is.
In my case, I generally like to run with resonant antennas and my IC-7610 doesn’t like to tune an SWR above about 3:1. However, my Elecraft K3 can manage SWRs of up to 10:1 and, even better, I have an Elecraft KAT500 tuner, which, with the Elecraft KPA500 amplifier, allows me to run 400W out into SWRs of, again, up to 10:1.
So, running with my Elecraft setup and playing in the LZ DX Contest in November, I was able to put the antenna through its paces and work all over Europe and beyond with no difficulty. Incidentally, and I have written about this before, if you are restricted antenna-wise, I see no reason not to make up for it by using as much power as our licence allows and it’s good that the Moonraker W3EDP is rated at up to 400W.
Conclusions
The Moonraker W3EDP antenna is certainly not unique to them – anyone can build one of these, albeit with the purchase of a suitable balun/unun. But the benefit is that the Moonraker version comes with the wires ready terminated, an end insulator, indeed all you need other than supports (fibreglass fishing poles are fine). And a single support would be fine for portable operation, with the top run out as a ‘sloper’.
This is a lightweight antenna that does, indeed, lend itself to portable operation. I was a bit worried that damp might get into the balun but Chris assures me the toroid is enclosed in potting compound so that shouldn’t be an issue.
I would also, to be on the safe side, advise against running 400W of CW or data modes into the antenna – a different situation to running 400W PEP on SSB.
The Moonraker W3EDP antenna sells for £49.99, which certainly won’t break the bank.
The Alpha J-Pole Sr
The description for this unusual antenna says “The Alpha J-Pole Sr Antenna is only 60ft in length. The unique design characteristics of this 10-160m HF J-Pole antenna enable it to approach resonance on the major HF bands (10/12/15/17/20/40/80m), all of which presents an SWR that is low enough for external tuners to achieve a near perfect match, including 160m.
“Configuration: End-fed configurable as Sloped or Horizontal
“Frequency Coverage: 1.8-29.7 MHz (16010m). An external tuner is needed for a few bands.
“Power Rating: 500W PEP SSB (200W CW or 50W Digital).
“An optimum installation would be where the antenna is deployed as a sloper with the high (feedpoint) end at 30ft or higher and the low end at 10ft or higher. We do not recommend installing this antenna as a Vertical due to users experiencing high noise (RFI) and unpredictable radiation patterns due to proximity of coax, which also allows for common mode feedback to increase”.
In Use
This antenna intrigued (and continues to intrigue!) me, if only because it’s not at all clear how it works, although it claims to draw on experience from wideband military antenna systems. It basically consists (see photo, Fig. 6) of two lengths of wire in parallel, one of 60ft and one somewhat shorter, connected separately to output terminals of what can only be described as a ‘black box’ (because I have no idea what is inside it). Actually, it’s described as a balun but that doesn’t explain the two (non-balanced) outputs.
The ‘black box’ is fed directly with coax and it is recommended that the feedpoint is elevated but the remainder of the configuration is down to the user (depending on what supports are available, what sort of QSOs you want to make – local, DX, etc – and so on).
In my case, I hung the antenna between the same two 20ft poles I had used for the W3EDP antenna, feeding the coax into the ‘black box’ at the top of the nearest pole. A check of SWR at the shack end showed
nulls on pretty much every amateur band, a result I wasn’t really expecting because I had assumed this was some sort of wideband antenna. The curve can be seen in Fig. 7. The actual SWR varied from 1.5:1 on 20m to 2.6:1 on the 12m band. Bear in mind this was measured at the shack end this time (because the feedpoint was inaccessible once installed), so includes any transformation effect from the feeder. What this meant was that my IC-7610 would happily work into it on all bands. The same, unfortunately, wasn’t true of my Expert linear amplifier (which is only really happy with SWRs of 2:1 or less) but, as before, reverting to my Elecraft line-up enabled me to run full power on all bands.
Again, and still during the LZ DX Contest, I was able to work very successfully throughout Europe and beyond (for example, into the US and Canada).
This antenna is significantly more expensive than the Moonraker W3EDP, at £199.99, but ‘felt’ to me to be more substantial and better suited to home station use.
Summary
The antennas reviewed are just two from the wide range available from Moonraker (see below). Both gave acceptable results and, in a sense, both are similar in that the radiating element is 60ft or so of wire. It can be argued that the only substantive difference is the way that wire is fed and matched. But the main differences are in the construction and the J-Pole is significantly more substantial than the W3EDP, which presumably accounts for much of the difference in price. Personally, I would think in terms of the J-Pole as a long-term homestation antenna, while the W3EDP would serve well for portable operations.
Incidentally, I hadn’t really looked at the antenna pages on the Moonraker website before. I was blown away by the enormous selection of antennas that they stock and sell. There really does seem to be something for all bands and all purposes – you just need to work hard on finding the right one for you! www.moonraker.eu http://AlphaAntenna.com