Provided with permission from Mr. Steve Nichols, Author of Stealth Antennas published by
Radio Society of Great Britain.
New antenna designs don’t come along too often. The spiral-coiled TAK-tenna is unusual in that although it is new, its design harks back to the early days of wireless.
Look at any old photographs of radio equipment from the early 1900s and you will see a lot of spiral coils – even inventor Nikola Tesla used them for the primary winding on his famous high-voltage coils.
The TAK-tenna is a dipole with each quarter wavelength radiating element made of a spirally-wound coil of wire. This was the principle behind Bill Petlowany’s (K6NO) design in the March 1998 edition of Worldradio. Less well known, but the most important person, is the original inventor A. R. Brown who patented his spiral version in 1969.
Stephen Tetorka, WA2TAK (hence the antenna’s name) in New Jersey, USA, is the developer of the newest version and he has a patent pending with improvements to previous designs.
The use of spiral radiating elements means the antenna can be made much smaller than the “full-stretch” wire dipole for the same frequency. To give you an idea, the 40m TAK-tenna version, as tested, has a boom length of only 30 inches and weighed 5lb. To put that in perspective, a full-size half wave dipole for 40m is 66 feet long. So the TAK-tenna is physically only 4 % of the size of a half-wave wire dipole.
There are TAK-tennas available for all HF bands from 80-10 M.
The 40m version can be used as a multiband antenna on 30, 20, 15, and 10 meters with a suitable ATU. There are many customer reviews on eHam.net giving TAK-tenna performance reports. Some operators use balanced line with low cable attenuation loss for off-resonance performance, in place of using a lengthy coax run to minimise power loss in the transmission line. Maximum performance is obtained when the TAK-tenna is resonated just as to be expected with the traditional wire version as resonance provides maximum efficiency for power transfer and it also provides more ‘user friendly’ impedance values when operated off-resonance in multiband operation.
Assembly is fairly straightforward. You insert the four coil supports into the boom ends and secure them with black mil-spec UV resistant locking cable ties. Pre-cut notches on the supports ensure proper wire spacing and the neat spiral shape. You then add the mast mounting hardware and mounting screws for the coax connections and feed wires. You also need to solder the tags and two crocodile clips to the two wires and ( unsupplied ) coax. The complete assembly took around an hour and it was ready for testing.
Once you have completed assembly you use the crocodile clips to pick the suggested tapping points on the spiral for the intended resonant frequency of your choice. The resonating process involves moving the crocodile clips to tapping points around the spiral until you get resonance at your desired frequency. The clips are removed and the wire ends soldered to the spirals once it is resonated. Some users resonate with a rig at low power and its SWR meter to locate the resonant frequency although using an antenna analyser makes this process much easier.
The end result in my case at the low height was a minimum SWR of 1.1:1 at 7.080 MHz with maxima of 3:1 at 7.000 MHz and 2.2:1 at 7.200 MHz. I could have moved the resonant point higher or lower, but as most UK operations appear to be below 7.100 MHz this was deemed OK.
I connected the coax to my Icom IC7400 to see how the TAK-tenna 40 performed. Conditions were not good in the middle of the day in July. The solar flux was 66, the A index 9 and the K index 1 and many Europeans were worked on 40m with 50-100W on SSB and CW. Compared with a W3EDP 85 ft end fed inverted L and 40m half-wave dipole signals were generally down 1-3 S points.
Raising the antenna height makes a difference for any antenna. At the manufacturer’s recommended height of 20 feet many signals on the horizontally orientated TAK-tenna were within one S point of the reference antennas. The resonant point moved higher in frequency as the antenna was raised and the tapping points had to be adjusted. The feedpoint capacitive impedance changes with the antenna’s height above ground due to capacitance-to-ground effect.
The loss of 1-3 S points is not all doom and gloom. On 40m at night there were many S9+20db signals that were a still a perfect copy at S9+10 on the TAK-tenna. In the IOTA contest many “59/599” reports were exchanged, although that doesn’t count for much!
In one QSO, Ike, DM3ML in Dresden, said that the TAK-tenna was 1 S-point down compared with the end-fed. Another good point is that noise levels were also down on the TAK-tenna – S5 on average versus S8 on the end-fed, which made for easier listening.
TAK-tenna recommends a statistical sample of at least 30 QSOs over a period of several weeks to assess performance under varying band and propagation conditions, and taking into account the antenna’s directivity and changing antenna patterns as more lobes are generated in a dipole as the frequency increases.
As one happy TAK-tenna user put it: “It works at 13 ft, better at 25ft, and is really awesome at 45ft! Imagine getting it up to 60ft? All with 100 watts.” TAK-tenna reports, maximum signal report is achieved when the cold spiral (the one connected to the coax shield) is pointing to the receiving station with reference to the boom centre.
Depending upon the specific site characteristics, vertical orientation may provided better results. It gives a lower angle signal suitable for DX, although mounting height is a factor. The instructions also state that you might be able to null local interference and peak signals by rotating the TAK-tenna directivity, although this wasn’t tried.
On the TAK-tenna web page there is an installation photograph of Vince Grgic’s, S52CC, TAK-tenna 40 jutting from his third floor balcony. With the MFJ-949E it tunes fine on eight bands from 80 through 10 M. Using the Yaesu FT-450 transceiver he has logged over 925 QSOs and 118 DXCC entities from 5 continents, some of them even in serious pile-ups.
I tried the TAK-tenna 40 mounted vertically at about 20 feet. The average noise level was higher (S6 against S5 when horizontal) but received signal strengths were generally only
1 S point lower than the reference antennas and sometimes equal. GB5FI on Flatholm Island was preparing for the IOTA contest and gave me 59 on the end-fed and 58 on the TAK-tenna. In his words: “The end-fed has the slight edge.” On CW some Europeans were equal to or 1 S–point stronger on the TAK-tenna.
At the time of writing, TAK-tenna has been in business three years and has maintained a customer satisfaction score on eHam.net of 4.7/5 - a 94% rating. That says a lot.
The TAK-tenna is a unique and useful antenna that would suit hams with little or no space for a full-size 40m antenna. Is it a compromise? Yes, signals were generally lower than on either full-size 66-foot half-wave antennas or an 85ft end fed, but then the TAK-tenna is only one sixtieth of a wavelength long on 40 M. And then, try rotating a wire either 66 or 85 ft long!
If you don’t have the room for a full-size 40m wire antenna ( or even if you do ) it will get you on the air with satisfying results.