Provided with permission from Mr. Steve Nichols, Author of Stealth
Antennas published by
Radio Society of Great Britain.
The TAK-tenna
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.
END