Commentary from the Founder
KA1PM
Below you will find a collection of writings from Tennadyne’s founder, Chuck Brainard (KA1PM). We offer these details for historical preservation, and to share some of the efforts that went into developing these superb designs.
While we continue to adhere to the overall design specifications, we also reserve the right to “improve” on the original features or components thru modern manufacturing practices and materials. Still 100% Made in America, each system is hand fabricated in our shop in Collinsville, Oklahoma. Using CNC technology we have been able to replicate some system components, however this is an expensive proposition as machinery cost and required shop space outweighs the benefit in most cases, therefore we continue to hand fabricate using original fixtures and tooling. It’s a slow process by today’s standards, but these methods ensure that we keep our costs in check while producing the consistent quality and performance that our customers have come to expect.
Chuck obviously had a deep understanding of LPDA design, far more than I expect to match. However, my background in manufacturing and product development ensures that we will continue to carry the torch for this long running brand, delivering high-quality and durable systems to users in the field.
I hope you can appreciate these writings, and the value that they have brought to our product line.
73, Mark (K5YAC)
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Specialized Design
Since 1986, Tennadyne has specialized in the design and manufacture of the broad-band Log-Periodic Dipole Array antenna, from 1.8MHz to 3.0GHZ, supplying these antennas to Commercial, Military and
Amateur Radio interests worldwide (since 1990).
Here at Tennadyne, we have used our antenna test range (not just a computer program that may or may not adequately address our subject) to enable us to thoroughly understand our product, all antennas under test are referenced against pertinent 1/2-wave dipoles. From this work, we have developed our own extensive and proprietary LPDA antenna design program.
“It’s as good as the stacked 3-element custom made mono-band yagis that I was using. It was a snap to assemble and install. Hugo (big hurricane) didn’t touch it.” – KE4FW, Al Pace [T10]
It’s a fact, nature is constantly trying to dismantle your antenna installation. Sometimes it’s a sledge-hammer blow like a major ice or windstorm. Most of the time, it’s a much less obvious… a simple and subtle, long-term dismantling involving water, corrosion, UV degradation and vibration. To counter this process as well as anyone can, Tennadyne antennas are ruggedly built, heavy-duty, top-quality beams consisting of high-strength, heavy-wall, seamless 6061-T6 alloy aluminum tubing and all stainless steel hardware. The tubes of our elements telescope one-part-to-another with a nominal fit of .0045″, and the elements fit into the precision machined booms with a .002″-.003″ tolerance. It’s proven, Tennadyne antennas take it through all kinds of weather and environments with little maintenance.
All are rated to 100 MPH!
– – – – –
HURRICANE GEORGES – FALL 1998
VP2EE reported sustained winds of 150mph with gusts to 180. Her T6 suffered MINOR bending and was easily straightened.
WP4W reported sustained winds of 130 MPH with 145 MPH gusts. His T10 suffered NO DAMAGE.
– – – – –
“I constantly get comments of “Strongest G on the band” or “outstanding EU signal.” Thanks for developing such a clever design and an antenna that really provides excellent value. I thought I was happy with the TH7, but the T10 is by far the best I have used.” – G3MLO, Peter Weatherall [T10]
An LPDA antenna is a frequency-independent device with unsurpassed frequency bandwidth and agility with close to equal performance at any point within its design parameters. Each of our LPDA elements is not only virtually 100% efficient, it also closely matches the 377 ohms impedance of free space, a further contribution to its efficiency. The real-world performance capabilities of an LPDA antenna are equaled or bettered by only perfectly designed, constructed and matched mono-band antennas of comparable or larger size.
MONO-BANDERS v. LOG-PERIODICS! – ONE BAND v. MANY BANDS!
“Many contacts were made “dead band.” Greatest advantage… being able to hear ’em.” – NØTM, Paul Flint [T10]
Tennadyne LPDAs use a double boom, one above the other, that perform a double duty. They act as (1) a constant impedance transformer, providing a constant impedance match between the very high impedance of the LPDA elements and your 50-52 ohm feedline. They also (2) provide a rigid fore-to-aft structure much like a truss, giving very strong mechanical support to the antenna elements. Overall, this boom structure is exceptionally strong! Each boom is precision machined so that the elements pass directly through, maintaining a constant impedance transformation!
This double boom is one of the things that distinguishes Tennadyne LPs from those of other manufacturers, and there’s more to it than meets the eye. In the Transmission Lines section of the ARRL Antenna Book, the text states…
“In installing parallel-wire line….the line should be kept away from other conductors, including downspouts, metal window frames, flashing, etc., by a distance of two to three times the line spacing. Conductors that are very close to the line will be coupled to it to some degree, and the effect is that of placing an additional load
across the line at the point where the coupling occurs. Reflections take place from this coupled “load”, raising the SWR. The effect is at its worst when one wire is closer than the other to the external conductor. In such a case one wire carries a heavier load than the other, with the result that the line currents are no longer equal. The line then becomes unbalanced.”
Every LP on the market must use a form of the open-wire line as a feedline within the antenna structure itself,
whether it is actually made of wire or, in the case of Tennadyne LPs, the booms themselves. Imagine, if you will, what happens when you run this feedline, from one end of the antenna to the other, only inches away from the grounded boom of the antenna. A clear reason why Tennadyne LPs are superior….by design.
“I am pleased with the performance of the T6; it allows me to move through the 20, 17, 15, 12 and 10-meter bands with the simple press of a button.” – K9LA, Carl Luetzelschwab [T6]
“In all cases, the RX and TX signals were stronger with the Log-Periodic (at 60 feet) than with the 4-element 15M beam (Mono-Band Yagi at 90 feet) into Europe, Asia and Africa.” – WB2WVC, Bob Johnson [T8]
“My Mosley TA53M never showed anywhere near this kind of F:B Ratio. At this point I am absolutely convinced that I have made a dramatic improvement over the Mosley.” – K2CA, Tom Eyring [T8]
Antenna Facts & Comparisons
“Best overall antenna performance appears to occur at an antenna height of about 1.5 wavelengths. On the other hand, heights over 3 wavelengths are most likely too high.” – W2PV
We recommend that Tennadyne antennas be positioned no lower than about .55-wavelength high at the lowest operating frequency. That’s around 38ft as a minimum for models covering the 20-meter band.
“F:B Ratio is as good or better than you claim and I find phenomenal nulls 90-degrees from the heading. This is a marked improvement over the trap tri-bander that I was using.” – WØAP, John McKinney [T8]
Free-Space Reference Antennas
“Conceptually, one can use free-space (fictitious) reference antennas, even though the real antenna is used over earth or ground. This has the difficulty, however, that one cannot experimentally make or use any of the reference antennas. Furthermore, the gain of an antenna referred to a free-space standard (dBi), even though quite correct, gives a value which is unnaturally high for most technical users.” – W2PV
Large Mono-Band Antennas v. The Log-Periodic Dipole Array
We all drool over the very large arrays on multiple towers that some hams have installed. This comparison of mono-band Yagis & Quads v. the wideband Log-Periodic Dipole Array will attempt to show what kind of differences really exist between various antennas. We did not include interlaced and multiband Yagis & Quads or antennas with traps.
In the following discussion, the net gain figures are the product of the actual gain of the array factored by its percent of
efficiency. For instance, any 20m antenna having a gain of 5.0dBd and a radiation resistance of 15-ohms will have an efficiency of about 83.3%, thus lowering the real world gain to 4.206dBd. In all of the following examples, the
comparison, + or – dB, is referenced to the Tennadyne T10 LPDA, on only 20m.
Yes, there are several mono-band antennas out there that have a little more gain than the Tennadyne T10, but you’ll need five of them to equal the T10 in frequency coverage. Would your ears notice the difference? Stacking and phasing a pair of T10s, or any identical antennas on the same tower, one at 110ft and the other at 70ft, realizes a gain of 2.6dB.
Multiple Antennas on the Same Mast
I’m often asked how much spacing is required when placing dissimilar antennas onto the same mast with one of our LPs. The following should help to explain my standard, “A minimum of 1/10 of a wavelength at the lowest operating frequency” reply, which is generally followed by my, “more is better.” With this, you can calculate your own requirements, the object is to keep adjacent antennas, of the same polarity, and their Effective Apertures, away from and out of the Effective Apertures of other antennas. You must consider the Effective Apertures of all antennas under study, the spacing requirement is cumulative.
The EFFECTIVE APERTURE (Area) of an antenna is calculated by: A = Wavelength2 G/4pi (All calculations are in feet)
A = Effective Aperture, or Area
G = Power multiplier (NOT dB) (Example: A +5.0 dBd antenna = Inverse Log of 5.0/10 = 3.16 = G)
Therefore, on 20M: A = 69.252 x 3.16/12.566 = 1206 = A
The radius of this Effective Aperture is then determined by: A/4.189 = r3 = 1206/4.189 = 287.9 = r3
Therefore, the Radius (r) of Effective Aperture in this illustration is: r = 6.6 feet
EXAMPLE: We want to stack one of those loaded 40M beams 10 feet above our 5.0 dB 20M antenna. Advertising aside, the reality gain of the 40M, loaded beam is in the area of 2 dB, which gives us a Power Gain of 1.58.
Therefore, on 40M: A = 137.32 x 1.58/12.566 = 2370
The radius is then: 2370/4.189 = 565.8 = r3 = r of 8.3 feet
The total stacking space thus required is 6.6 + 8.3 ft = 14.9 feet
Four stacked T12 LPDAs at K1KW
Dr. James L. Lawson
1927-1993
Since there has been mention of W2PV in our analysis and discussion, we felt it prudent to provide a brief introduction for those who aren’t aware of his contribution to wireless communications.
Dr. James Lawson was a retired physicist and planner for the General Electric Company, where he was R&D Manager of Research and Development Planning for the company during the 1970s. His efforts contributed to the development of radar, nuclear-particle accelerators and general electronics. He was also involved in helping to develop an advanced form of atom smasher, known as a non-ferromagnetic synchrotron, that was utilized to study the effects of high-energy radiation in nuclear research. He also directed work in integrated circuitry, solid-state physics, military communications systems and computer science.
An avid Amateur Radio operator, Dr. Lawson won several competitions (radio contests) using his highly custom and well-equipped station that included many large and self-designed antenna systems. Publications include a series of articles in Ham Radio magazine (1979-80) and he authored “Yagi Antenna Design”, published by ARRL in 1986.
W2PV – SK (1993)