>
>At 11:47 AM 2/4/01 -0500, you wrote:
>>> No, but I wonder how they relate to F/R bandwidth, gain bandwidth and
>>> SWR bandwidth. A lot of work has been done to get all three of these
>>> in reasonable balance, and I don't recall any 3-element solutions that
>>> have actually yielded 50-dB F/R over anything like an entire band,
>>> much less in combination with acceptable SWR bandwidth and a fairly
>>> flat gain curve in the range expected for such antennas.
>
Tom ,
You didn,t answer the above questionS! And they were very good questions
and very pertinent to the main theme of this thread
In a forum, standing on a box with an 'OH yayyy"
like Andy Capp just doesn,t cut it.
You made your points about what can,t be done and then walked away.
I know of no company that has succeeded that wallows in what can,t be done
but I know of many successes by those who probe the known boundaries and build
upon it,s successes.
Getting back to the subject posed by Peter ,which was your big 3 element
antenna.
What is the FRONT to REAR? What are the other specs?
Is it desirable and if not, what can you say that will contribute to make
it desirable.
Shurely it isn,t just that deep null that you are heavily enphasising.
He also asked some other relavent questions but you turned a deaf ear. Why ?
This is a Forum not a chat group !
What are your expectations for a good antenna and is it attainable
by the masses? To just yawn and say 'forget yagi,s.' suggests that you have
no more to contribute. Surely that isn,t so. If it is why are you here?
Let me help you to become more positive
I would like a yagi to have 'good'flat front to rear across the band. The
same goes
for flat gain and a flat realistic drive impedance The antenna I posed
with 3 reflectors meets that target or goes along way towards that end.
This antenna came up
as a response to a post regarding extra reflecters and their physical length
and we are certainly along way from that theme.
I am not flaunting it,you entered the thread and responded with your
huge 3 element beam for 40 or was it 80. It sounds like a terrific
eye opener but without specifics and overall relevance it really
screws up the thread.Where exactly are you coming from?
Does your 3 element yagi meet all YOUR goals with respect to performance
across
the band.
Are there some areas YOU 'wish' you could improve upon, putting
aside heavy emphasis on known resons why it CANNOT be done ?
If you would answer Peter,s direct questions
we could have a more positive idea of your disposition to this thread
and where you are coming from, as a predator or a contributor.
Be positive, answer Peter,s questions so we can get back on track
Have a happy day
Art Unwin KB9MZ
>
>
>
> want truly wide-band performance...forget a Uda-yagi
>>antenna. Its primary advantage is simplicity, not bandwidth or
>>performance.
>>
>>In a purely endfire array drive all the elements with cross-fire
>>phasing, and use transmission lines or simulated transmission
>>lines instead of lumped components.
>>
>>If the physical shape or style of array is not critical, then use a
>>broadside antenna with a non-resonant reflector system (like a
>>screen or grid of wires).
>>
>>You can get octaves of bandwidth using either method.
>>
>>For Ham use, a simple yagi or array of yagis is plenty good. I live
>>in a rural area with very few buildings or uncontrolled metallic
>>objects around my antennas. Even in my very open environment,
>>ionospheric scattering and multi-path limits useful antenna null
>>depth to perhaps 20 or 30 dB. If you shut the door more than that,
>>it does no good. You still hear the backscattered signals from the
>>rear.
>>
>>Unless the antenna occupies a large physical area in terms of the
>>wavelength, it is impossible to remove radiation from a substantial
>>area.
>>
>>Adding elements without increasing occupied area, in an attempt
>>to force a wide null area with a physically small antenna, quickly
>>causes the element currents to become excessive. The elements
>>have destructive interference even in the desired directions, so the
>>array "fights itself".
>>
>>This is called "superdirectivity" in antenna textbooks, and is readily
>>discussed with appropriate warnings about high Q, low efficiency,
>>and critical operation.
>>
>>BTW, don't confuse an engineering discussion of superdirectivity
>>with the amateur radio term "superdirective" used in antenna ads.
>>The recent term is borrowed from some article in a Ham magazine
>>(I think it was Comm Quarterly) as sales fluff.
>>
>>There is no free lunch...and there are very few cheap meals worth
>>having.
>>73, Tom W8JI
>>w8ji@contesting.com
>>
>>--
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>>
>>
>>
>
>
>
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