Exploring the Diamond 144S-5 & A144S-10 Antennas
Richard Constantine G3UGF reports on using two lightweight portable antennas for the 2m band.
Isuppose everyone likes to re-live their youth at some time or other and I’m no exception. In the pre-computer logging, hybrid radio, valve amplifier and heavyduty petrol generator days (real radio) I was a keen /P, VHF/UHF contester with my local club.
In 2019, I planned to re-visit my youth as a solo operator. The PW 2m low power contest seemed an ideal re-introduction, as I could still use paper logging, QRP and it’s a ‘no ADIF file required’ contest. How that dates me!
Aiming to operate locally at around 400m ASL in Yorkshire, I figured that I didn’t need a huge antenna as in days of old. All I was looking for was something with reasonable gain that I could raise myself as, once an antenna is a couple of wavelengths high, it’s not really subject to much degrading ground effect anymore.
Add to that the increased range of horizontal polarisation with its small, contour hugging, over the horizon benefit, plus SSB and I figured that I should be able to make a reasonable fist of things with something relatively simple.
Antenna choice: A144S-5 vs A144S-10
Casting around, the Diamond A144S-5, 5-element Yagi seemed to fit the bill, regardless that at today’s prices, circa £50.00, it costs as much now as my now long gone, Cushcraft 19 element Super Boomer!
Note: From here on, most information in this article also applies to the Diamond 10-element version, unless explained.
The 5-element arrived nicely packed, with the 9mm capped, hollow, tubing elements already in their insulated mounting saddles, on the 20mm diameter boom. No chance of getting it wrong, I thought. All I had to do was slacken the mounting wing nuts, swivel the elements 45°, re-tighten and ensure that the pre-marked centres of the elements aligned in the centre of the boom saddles nice and foolproof… well, almost.
Surprisingly light, at a total weight of 700 grams, and 950cm in length, there was going to be no issue with mounting or raising this antenna on mast sizes up to 35mm (1.5in) diameter plus, it came complete with an appropriate bright metal, through the boom, U-shaped, mast clamp. The boom being conveniently pre-drilled for both horizontal or vertical mounting.
The slightly larger diameter driven element, so as to maximise the radiating surface area, was separately packed and mounted easily on to the boom. The central connector box has a locating lug that sits into a pre-drilled hole in the boom, to ensure it’s correctly spaced, doesn’t twist out of alignment and the whole thing is secured by a captive wing bolt, already on the boom. Diamond say assembly time is three minutes and that to my mind is a conservative estimate. A backpacker could easily do it in that, in a hailstorm.
More on the Construction
All of the ancillary steel metalwork is plated. Thankfully not like the old cast alloy, saddles and wing nuts I remember of the long-gone J-Beam days, when they were the only antenna game in town.
While plated components might eventually rust, and need silicon grease or other protection for a permanent installation, at least the Diamond nuts won’t oxidise, fracture, or simply powder to dust.
I was thankful that assembly proved to be intuitive as the 5-element paperwork supplied was in Japanese. The later 10 element version thankfully arrived with both English and Japanese documentation.
Looking at the construction, I wondered why the power rating was limited to 50W carrier maximum, and what could be inside the sealed connector box. Logically, it was too small for a T-match, the driven element wasn’t a folded design and both halves of the element were a DC short. It had to be a 1:1 balun match. As it’s a weather sealed and riveted box, I wasn’t for opening it.
Oddly, the reflector element appeared visually shorter than the driven element when design convention dictates that it should be around 5% longer. Most puzzling.
Fig .1: Polar diagrams for the two antennas, both singly and when bayed. Photo 1: A144S10 on painter’s pole + van. Photo 2: A sky view of the 10 ele. Photo 3: Close up view of the 10 ele mast mount and joint clamp. Photo 4: The 5 element antenna.
Initial Evaluation
During my evaluation of both this and later its big brother the 10-element, I noted a number of queries and contacted Diamond in Japan. They responded both quickly and courteously, as is the Japanese way. I engaged with one of their design engineers who confirmed that the driven element is indeed balun matched as this produces reliable and repeatable results for users. Despite appearances, the driven element is physically shorter than the reflector as the two halves of the driven element are separated by the balun. The balun match dictating the power handling.
The closely mounted first director is also helpful in matching to 50Ω over the natural 75Ω impedance of a dipole. Bandwidth is indeed excellent for UK use.
Having some concerns about the use of plastic-type element saddles and the possibility of de-nature of the material, I enquired about the antenna’s longevity. I was advised that the materials should be good for around ten years of use, subject to the usual weather caveats. Hmm… “What about climate change”, I hear you say.
Well, what amateur doesn’t change his or her mind about their antennas in ten years?
As always. the use of a shiny metal, average quality, low cost, SO239 socket concerns me when it really should be a silver plated, PTFE, N type at both VHF and UHF for low loss, best performance and weatherproofing. Unfortunately, changing the socket isn’t really practical unless you are determined, due to the mounting and sealed nature of the box.
In the design of the both the 5 and 10 element versions, provision has been made for horizontal stacking and vertical baying of these antennas.
Not so common in the UK but popular in some other countries, baying two antennas typically provides around 2.5dBi of gain. Diamond produces cables and bracketry for this purpose and there’s some guidance on the leaflet supplied. I can’t confirm that kits are available in the UK as UK importers tend to cherry pick what sells - can’t blame them.
Stacking and Baying
Baying antennas particularly for vertically polarised FM use increases wind and head loading on masts.
For interest, look at the 3dB point polar diagrams in the plot, Fig. 1. The beamwidth and available gain makes for an interesting comparison between 2 x 5 element bayed or a single 10-element. In some locations the former may prove a better bet, especially if you factor in the bird’s eye view from the mast and the surrounding take off. For my purposes as a mainly portable operator, the single 10-element version of the antenna, gives the same claimed gain figure as the bayed antennas, despite the increase in wasted energy in larger side lobes.
Real Gain. dBi or dBd?
This brings me to the thorny topic of gain. I grew up learning that gain should be referenced to a dipole of the same frequency in free space or, a vertical quarter wave and radial/grounding system and noted as ‘dBd.’ Decibel gain over a dipole is a reference to a real-world antenna, used as a baseline for measurement.
The 80’s CB boom brought with it the need for makers to out-claim each other in terms of gain as a selling feature and there were some outrageous claims. Gain figures claimed in ‘dBi’, that is Decibel gain over an isotropic radiator, look bigger and sell better! In truth there is no more real gain, it’s like Fahrenheit and Celsius, but dBi is where we are now. Diamond’s single, 5 elements is rated at 9.1dBi and the 10 elements at 11.5dBi.
While the more director elements you add and the longer the boom becomes, gain increases but the beamwidth decreases, making the pointed direction more critical. Here again a look at the polar diagrams is quite revealing. For contesting, narrower beamwidth is both a blessing and a curse. Yes, you have more signal gain but, the longer the antenna, the more times you have to re-direct it, when all you want is
enough signal for a quick exchange, not a hifi report. This is yet another consideration if choosing an antenna for /P and contesting. You need to always consider the logistics of mast requirements, wind and weather etc, especially if you are on your own.
Adding directors and extending the boom is perhaps where the magic happens. Experimenting, playing with the dimensions and judiciously arranging the distances between elements can result in improved gain and with it a small increase in performance. Of course, creating a one-off is not the same as manufacturing a production model with guaranteed and repeatable gain figures, time after time.
Practical Comparisons
Returning to conventional theory and accepted wisdom, I expected to find the director elements decreasing in size towards the front, by around 5% per element, hence why they arrived pre-mounted on the boom etc.
This is true for the 5-element version and the front director is wider spaced from the fourth to maximise gain. It’s more than easy to think that the 10-element version must simply be the same antenna with five more elements added. Not so. They are, to some extent, different designs.
I must confess I had considered homebrewing an add-on of my own to the five elements. Now I’m glad I didn’t. I might have wasted many hours fooling myself, struggling to achieve better gain figures.
The 10-element version has a split boom that neatly joins by means of a slotted, plated steel, over tube. Thoughtfully, you don’t actually have to remove the through-theboom jointing bolt and wing nut to fit the two together. All that’s needed is to slacken the bolt enough for the two halves of the boom to snugly and accurately join, before tightening. There’s little chance of losing the bolt and wing nut in the long grass as someone has actually thought this through. Full marks Diamond!
Considering the 10-elements, eight of the directors are the same size. The reason given being that not only does this make production more straightforward but also has band/ beamwidth benefits while maintaining the claimed gain figure. It wasn’t a problem. Like the smaller version, directors 9 and 10 on the larger antenna are slightly wider spaced. Overall, the A144S-10 is 1.2 m long and weighs a mere 1.2kg.
An unconventional looking feature is that elements 4 and 5, located either side of the mast mounting U bolt and not to be confused with the boom jointing tube, are much closer together. At 12.5cm apart they are typically only half as far apart as the other directors. I will leave you to work out the fractions of a wavelength maths on this one.
I’m assuming that it takes care of interference from the supporting mast while presumably maintaining the overall impedance and performance.
Final Scores
Having satisfied my curiosity concerning the designs the real-world test was to be the PW2m contest. In 2019 there were 72 entries. My result, 18th place, not bad for just 5 elements on a short ‘painters’ pole.’
This year, the extra five directors and revised design of the A144S-10 made possible an additional 11 contacts plus, most importantly, three additional, distant bonus squares. Of course, band conditions may take some credit, when measured against others’ scores.
Final scores were published in last month’s issue. My score improved by around 40% thanks to those extra few contacts and vital squares, gaining me 11th place overall- result! I think of contesting as being a little like golf. It’s always nice to win. It’s unlikely but I’m really trying to improve my handicap.
On reflection, perhaps the next move in 2022 is to forego my original ideas and increase the antenna height after all, so as to just to see a little further beyond the horizon.
Final Ratings and Impressions
In today’s marketplace both antennas offer the user cost-effective, straightforward, nofrills assembly, reasonable gain and most creditable performance. They are lightweight and well designed. Bandwidth on both models is excellent and has been factored into the design by making use of the balun matching and the clever element dimensions and spacing. This makes them ideal for use right across the UK band. The trade-off being the limited power handling.
These antennas are not aimed at the dedicated QRO operator. The target market being the sub-100W PEP and 50W FM, average user.
The makers claim a lifespan of 10 years for all of the components but I still have some reservations, without additional protective measures.
As for the final scorecard. The A144S-5 is for me a 5-star portable antenna, for hill-topping, SOTA and casual /P use, no question.
The 144S-10 is a great antenna for the money and scores much the same as the 5, when used in the same settings. Hopefully, I’ve demonstrated it has much to recommend it over the smaller version
However, for long term fixed station use, particularly in an exposed location and if the user is contemplating running high powers, now or in the longer term, perhaps an alternative is a consideration, albeit at higher cost. In this potential scenario my star rating drops to 4 overall.
Diamond antennas are available from a number of UK sources, typical cost at time of press (from PW advertiser Moonraker), 5-element circa. £50.00 and 10-element £80.00.
A Footnote from History
The name Yagi is really a misnomer. The antenna should be called a, Yagi-Uda (or maybe the other way around). Firstly, the subject of work at the Imperial University of Japan by both Shintaro Uda and Hidetsugu Yagi. Shintaro-Uda published a theoretical paper in 1926. However, the patent was filed by Yagi in his own name and later became the property of the Marconi company. Largely overlooked in Japan until WW2. Following the fall of Singapore, it was realised that airborne radar antennas of this design were being used by the British and Americans. Search the web on this topic. It makes for fascinating reading.