[TowerTalk] InnovAntennas contact info

[Joe Subich, W4TV]

> If these antennas have been so extensively modeled and optimized,
> there should be a clear comparison available that would tell us
> whether the difference warrants the hype.

Do just a little literature search for yourself rather than expect
that UPS will deliver a box of books customized for your skepticism.
There have been dozens of patterns posted on Justin's personal web
site over the last couple years as well as journals in the area and
web sites of other antenna developers.  The data is out there but
nobody is going to spoon feed the skeptics.

73,

    ... Joe, W4TV


On 3/20/2013 1:52 PM, David Gilbert wrote:
>
> I am perfectly willing to accept that a loop fed array (LFA) lends
> itself to some advantages for optimizing performance.  What gripes me is
> that whatever advantages there may be are described in purely marketing
> terms with zero quantified comparisons.  Where is the data that supports
> any of this??  If these antennas have been so extensively modeled and
> optimized, there should be a clear comparison available that would tell
> us whether the difference warrants the hype.
>
> That's all I ask ...
>
> 73,
> Dave   AB7E
>
>
>
> On 3/20/2013 10:36 AM, Ian White wrote:
>>> On 3/19/2013 11:10 AM, Joe Subich, W4TV wrote:
>>>> They give the designer additional degrees of freedom with which to
>>>> control input impedance and side lobe structure.
>>> I was with you until you said "side lobe structure." I don't claim to
>> know much a
>>> bout the design of Yagis, but I'm under the impression that pattern is
>> largely
>>> determined by the tuning and spacing of parasitic elements. Am I wrong?
>>>
>>> 73, Jim K9YC
>> The radiation pattern of a Yagi is determined by ALL of the elements,
>> including the driven element itself.
>>
>> As a volunteer editor for the German-English VHF/UHF magazine DUBUS, I
>> worked on several of the original articles by Justin Johnson, G0KSC,
>> that first introduced the LFA (Loop Fed Array) and I have watched with
>> interest as the concept has developed. Recent years have seen a big leap
>> forward in Yagi design, and the LFA has played a major part in this.
>>
>> G0KSC's original design work was aimed at extreme weak-signal
>> applications such as moonbounce and terrestrial VHF/UHF DX, where the
>> ultimate signal/noise ratio is often spoiled by the pickup of noise from
>> minor lobes of existing long Yagi designs. Suppression of minor lobes to
>> levels of -20 to -30dB requires very precise cancellation between the
>> radiation contributions from all of the Yagi elements summed together;
>> and at this level of detail, broad generalizations don't work any more.
>> Progress can only be made by very careful computer modeling and
>> optimization - and by questioning all the old assumptions about what
>> makes "a good Yagi".
>>
>> To cut the story short, G0KSC found that a horizontal open-loop feed
>> allowed a Yagi to designed with an excellent combination of
>> characteristics: high gain (for the boom length employed), minor lobe
>> suppression of at least 20-30dB, a 50-ohm feedpoint impedance, and broad
>> bandwidth in two quite different respects - not only a good VSWR
>> bandwidth but also a good "pattern bandwidth", meaning that the
>> radiation pattern remains relatively stable across a wide frequency
>> range.
>>
>> As W4TV says, the loop feed gives additional degrees of freedom in the
>> design. It seems to open the door into a particularly favorable area of
>> parameter space, where several good performance characteristics come
>> together and computer optimization can offer some very useful practical
>> designs.
>>
>> Of course these computer-optimized designs then needed to be proved in
>> practice - and to be fair, I think they now have been. The InnovAntennas
>> company has been built on the good reputation of the LFA designs among
>> moonbouncers and experienced VHF/UHF DXers, who have tried the antennas
>> and measured reduced levels of noise pickup from the rear and side lobes
>> compared to their previous arrays.
>>
>> Now here's where the story becomes even more interesting. While
>> continuing to develop the LFA concept, G0KSC also revisited other more
>> conventional Yagi designs that had been written off 50 years ago as
>> 'evolutionary dead ends' - in particular, some designs with a very low
>> feedpoint impedance around 12.5 ohms. Guess what? With modern
>> optimization techniques, these conventional straight-element Yagis can
>> deliver very similar sidelobe suppression to the LFA.
>> Spurred on by that discovery, other designers such as YU7EF, DK7ZB and
>> G4CQM joined the charge and began to create their own designs using
>> conventional straight elements, with similar good results.
>>
>> The latest development area seems to be in bent driven elements, such
>> the C-shaped 'OP-DES' concept of G0KSC and the V-shaped elements
>> favoured by some other designers. Once again these specially shaped
>> driven elements are giving the designer some extra degrees of freedom to
>> optimize the overall performance.
>>
>> We now know that many different types of Yagi design can be optimized to
>> give excellent suppression of minor lobes across a good bandwidth... at
>> least within a computer optimization environment. The real
>> differentiators are probably much more practical: ease of translation
>> from the computer design into real hardware without loss of performance,
>> ease of feeding from 50 ohms and of course a dependable mechanical
>> design.
>>
>> Every contributor deserves credit for these new developments in Yagi
>> design, and in particular everyone else gives credit to YU7EF. But it's
>> also fair to say that G0KSC has led the charge with his innovative
>> designs and prodigious work rate, and has raised the bar for everyone
>> else to match.
>>
>>
>> 73 from Ian GM3SEK
>>
>>
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