What we say about the antenna (click here)
Does it need planning permission? (click here)
What Force 12 say about the antenna..........
The need for efficient vertical antennas has been evident for many years and, as a result of customer requests, the Force 12 ZR-3 was developed several years ago. This small, 6' tall antenna is an effective 20-15-10 meter vertical dipole and needs no radials. The ZR design has been provided to commercial customers for many years with excellent success; however, it is expensive to build and somewhat difficult to install. A new design was needed with the same efficiency, easier assembly, tuning and installation. The result is the SIGMA design. "Sigma" is the Greek mathematical symbol meaning "the sum of" and the SIGMA series is truly the sum of years of experience, designs and testing. Not all ideas were successful, but that is the manner of research.
The Sigma 5 is a true Vertical Dipole, covering 20-17-15-12-10 Meters - It has NO Traps, and is >90% Efficient all bands. Rated at 1,200 w PEP SSB, 700w CW.
At 9' tall, with an 18" Base Post it's the answer to neighbour and planning problems. There are NO Radials, and SWR's are - <1.8:1 on 17-10m, >300 kHz on 20 mtrs. It comes in 2' Sections for easy shipping, and DX-pedition use. Free Standing, 7 Pounds weight. Simple Assembly - NO Tools - Pre-tuned
This is a brand new, high performance vertical for the 20-17-15-12-10 meter bands. The SIGMA-5 is the answer for an efficient, non-trapped, low profile, lightweight vertical. The SIGMA-5 follows in the footsteps of the SIGMA-40 and SIGMA-40XP single band 40 meter antennas, which were first in the SIGMA line - the result of 4 years of research, testing and development, including DX competitions with "Team Vertical" and several DXpeditions. If Force 12 knew how to make it better, they would do it! The only thing to enhance a SIGMA antenna is to place it adjacent to salt water.
What WE have to say about it.........
30 August we had delivery of our first Sigma-5. We have always taken a cautious approach with small antennas, believing that only the most careful electronic and physical design would allow them to perform well. That's why we ordered just one rather than a quantity. This particular antenna was already sold to a customer, so we were only able to test it for a couple of days. We are now going to order another ten. Read on............!
The antenna arrived in a small carton, certainly small enough to fit in the boot of any car, or indeed to be packed into a suitcase and taken on a plane. It's also quite light at only around 7 lbs weight. Here's a picture of all the parts. The white thing to the right of the picture is a one-foot (30cm) ruler.
The antenna was next assembled, without having first read the instructions (I always like to do that!). It went together in just 15 minutes, no tools being required. Each tubing section fitted into the next easily, everything being fastened together with stainless screws and wing-nuts. A short pigtail with a female UHF connector (SO239) was provided for the feedline, and 50ft of control cable and a remote switch comes for bandswitching the antenna.
Here is a picture of the assembled antenna - Father, and son helping
The need to switch the antenna is a small price to pay for avoiding traps and other things that go wrong. Also, the full length of the antenna is in use on all bands, instead of the trap method of wasting most of the antenna length on the higher frequencies. There are no radials, and a bucket of old bricks was used as a temporary base for it. It was a very easy installation, and very fast. Just the job for portable HF (and before you ask - yes, someone in the USA already has one mounted on his car!)
Although many cusomters ask us if it is beneficial to mount the Sigma up high on a mast or tower, the advice from Force 12 is that the antenna will work no better than at ground level, indeed the vertical angle of radiation is likely to increase if the antenna is at a height. Because of this our Sigma 5 was positioned about 20 ft away from a two-storey brick house, with the lowest part of the bottom element just 1 foot off the ground. The feeder and control lines were led off at a 45 degree angle and then run along the ground to the shack. Several comparison antennas were available -
Large (24ft boom) triband yagi at 110 ft
2-element full sized 18 MHz yagi at 50 ft
HyGain 12-AVQ trapped vertical antenna -14ft long, at ground level. We have used this one on DX-Peditions and it is a known OK performer.
Tests commenced with VSWR measurements. The Force 12 specifications were met in full, ie, the coverage was below 2:1 throughout the range of all bands except for 20m, where 300 KHz was below 2:1 (The 300 KHz may be adjusted within the band). Typically the VSWR was below 1.5:1 on most of the bands. High power tests were made with 500W RF output and no problems were noted. Tom Schiller at Force 12 told me that field units were happily being used at the USA 1500W pep level, with no burn-ups or breakdowns.
A series of on -air tests then took place. In all cases the Sigma5 obtained better reports both transmit and receive on 20-15-10m than the 12-AVQ. Usually the difference was about one to two s-units.
Although it does not mean a great deal (often a test of conditions rather than the antenna) the following countries were worked in some limited operating time one afternoon and the next morning with 100W and the Sigma 5. At this stage of the sunspot cycle there is not much going on on 12 and 10m, which explains the lack of contacts. Even with the beams there was very little activity to be found on those bands. All stations worked were CALLED with 100W and the Sigma before making comparative tests with the other antennas.
10m PY7ZZ gave 57
12m YB9BON, 9E0S (Eritrea) gave 599, RZ9MYL gave 57.
15m PY7ZZ, EA8FO, TA2MW, W's gave reports varying from S6 to S9
17m OD5/OK1MU, VK3DOU 5Z4TT, ZD7BG,several W's including one W6. Reports from 579 to 59(9)
20m JA7EYL, VK4FWH, W's. Reports from 569 to 59(9)
Notable moments..... Breaking a pile up for 5Z4TT on 17m and working him first call!.........VK4FWH giving 57 for the Sigma on 20m and only (!) 59 for the 3 ele yagi at 110 ft. ZD7BG giving 569 for the Sigma and 579 for the 2el yagi at 50ft on 17m. Indeed it was with great regret that the antenna was handed over to a customer this Saturday.....
Comments....
- During the period of testing the British Summer definitely ended with deluges of cold rain. The performance of the Sigma-5 was entirely unaffected by it.
- I wanted to optimise the 20m SWR (factory set to bottom at 14220) to 14100 to reflect my CW interests. This was easy, and involved a simple adjustment to the aerial.
- There were several times during the testing when the big HF beams were entirely useless as rain static raised the S-meter to S9 plus 40dB for minutes at a time. Signals were still clearly copiable on the Sigma-5
- Harmonics are suppressed as the antenna switching results in monoband performance, with no trapped sections resonant at harmonic frequencies.
- Unlike conventional unbalanced verticals (fed against radials or a counterpoise system) the Sigma-5 is a true vertical dipole, balanced, with ferrite balun, to assist in suppressing feedline radiation - often the cause of TVI from vertical antennas.
User Report from experienced DXer Bob McHenry G3NSM.
Yesterday I decided to see how long it would take me to Work All Continents
on all three bands, 10, 15, 20 during the CQWW CW contest using the Sigma. It took almost exactly two hours to make the eighteen contacts necessary. I could have done it more quickly if I hadn't picked out some difficult ones and had to wait my turn in the pile-ups. Here is what I worked. 14 VK4DX, 9M6NA, XT2DX, HC8N, W6XR, YT1BB 21 VK8AV, EX8O, XT2DX, PJ2T, J3A, IK6SNQ 28 VK6PZ, VU2PAI, ZD8Z, PT5T, VP5G, S53EO I used maximum legal power with the Sigma at ground level. Conditions were not particularly good because there was a severe geomagnetic storm in progress. Three WACs in a single two hour period isn't bad in the circumstances and suggests that the Sigma is a really effective little antenna.
And the best news
The Sigma-5 is normally £349.95 / €560.00. Please ring us now to place an order.
UK Planning Consent (many ask!)
Despite the opinions of many self-appointed experts, the UK planning rules are quite clear. Any structure higher than 3 metres above ground level (10ft) needs planning consent. The Sigma 5 (with the supplied base) is 10ft 6" tall. We haven't tried shortening the base by 6" to bring it within the magic 10ft (the buyer of the antenna would not like us to do that!), but it is unlikely the performance will be affected. Besides, we defy anyone to tell the difference between 10ft and 10ft 6" over a garden wall. We aren't aware of any other multiband vertical antenna that will meet this size requirement and still radiate efficiently, so the Sigma-5 is truly the solution to the impossible QTH / crazy planners problem.