[TowerTalk] Re: Yagi's
art unwin
aunwin@fgi.net
Tue, 06 Feb 2001 11:37:30 -0600
At 05:47 PM 2/5/01 -0500, you wrote:
>Art,
>
>I'd like to see your element lengths to check them on my modeling program.
>13 elements on a 1 wavelength boom is quite an aluminum antler! Can you
>send me the data?
Well hi Joe,
Thank you so much for stopping by, I delayed in reading it because of some
inner fears which now appear to be unfounded.
I have visited G3SEK pages many times on
long boom antennas which features your impressive past
ventures in this particular area.
I noted the many plots with' split' forward lobes which are not for HF
discussion together with the formula that defines gain that include the
number of directors which also presents a window to me that I have never
considered before but gave me cause to consider in this long ongoing project.
With respect to "aluminum antler "
In normal thinking that is what one would expect. But it is not so.
If the thread had continued or others showed interest and got involved
I think I would have surprised a few people in how in how I stepped back
and reevaluated antenna construction on my own terms.
With out heed to preconceived barriers in the light of present
day materials combined with my enginnering past and consideration
of known problems that can occur when turning a so called 'flywheel' .
But that can be shared another day !
I will readily supply the info requested in a separate E mail
Frankly I have been astonished by the 'on the air' abilities of
this type of antenna and am gratified that you are taking a' look see.'
I also would be very happy to supply photo,s of construction, raising
procedures and antenna up and material pictures together with any
pattern data and personal experiences over the years with this particular
animal.
My original intent with this material was to write it up but I have since
lost interest and thus have no need.
Last week we had an ice storm and my ideas came thru just great!
I didn,t welcome the test but it removed a great concern from my mind
Email info to follow with requested data.
Your enquiry has given me great joy even tho my expectations are low.
Art Unwin KB9MZ
Note additional comment below
>
>My 1 to 1.1 wavelength 50 Ohm Yagi antennas designs (no matching required)
>use one reflector and 5 to 6 directors.
>
>In the August 1977 Ham Radio Magazine I wrote up the Trigonal reflector (3
>reflectors) used by the NBS antennas. Later I found with computer modeling
>that it decreased efficiency and moved the rear lobes to another plane!
>Also, the NBS lengths turned out to be incorrect so I redesigned same (had
>to lengthen them) and then designed what became the Cushcraft 2-meter
>BOOMER antenna line.
>
>I now have better and cleaner Yagi designs and no longer find a need for 3
>reflectors....providing.... that you properly design the director structure
>(spacing and element length).
>Great I also went down the triagonal path and frankly I found it overated
in it,s abilities but it does show how extra elements can help in other ways
other than gain e.t.c. by providing reasonable impedances to continue the
pursuit
of a "better antenna" instead of a folded feeder (dipole)
It all depends what target you are aiming for in final use.
>In the Winter 1998 issue of Communications Quarterly I gave some tips and a
>great 4 element Yagi with a 50 Ohm feed.
>
>73,
>
>Joe, W1JR
>
>
>
>At 12:31 PM 2/5/01 -0600, you wrote:
>>At 10:27 PM 2/4/01 -0500, you wrote:
>> >Hi Art,
>> >
>> >You made the claim yagis can't have more than 20-25 dB F/B or
>> >F/R, and that is not factual. My 40 meter antenna is an example,
>> >and I'm sure there are countless others.
>>
>> I did ?
>> I used the word " can't" ?
>>
>> I wish you had specifically mentioned that sooner.
>>
>>Ofcourse, that is completely incorrect as a single statement on it,s own
>>I am bemused that no one took me to task other than you
>>
>>
>> >As a matter of fact with two driven elements in a phased array, I
>> >can get a null that for all practical purposes goes to zero.
>>
>>
>>True Tom but for amateur antennas you would be foolish to purchase
>>an antenna based on one statistic, let's keep apples to apples
>>and keep to the theme of the thread or it becomes just a bunch
>>random words or statistics.
>>
>> >stations do that all the time, to protect other stations.
>>
>>Oh I,m sure you are correct.I've heard of zero reception when
>> in 'spitting' distance of the antenna. But that is with verticals!
>>I don,t think you can extrapolate those experiences and relate
>>them to Yagi's. But since you have brought it forward I am
>>interested in hearing more about that particular yagi,
>>it sure sounds unique and raises interesting questions
>>
>> >If you doubt my antenna or other three element yagis can have that
>> >null depth, I can e-mail you an Eznec file showing they do.
>>
>>Oh theres no doubt that any antenna can get a spot rejection
>>of high levels but if I remember correctly I stated a particular
>>rejectionb in association with it's accompanying high
>>REAR REJECTION figures.
>> Surely you recocognise the difference. You focussed on the
>>spot rejection null and choose to ignore the other salient information
>>when you brought forward your massive 3 element beam and moderate
>>rejection point figures.
>> This choice of manipulating supplied statistics
>>and ignoring others distorts the debate, and that was why another poster
>>made mention of it. Ofcourse every body knows that the the antenna
>>you brought forward has very poor REAR rejection rates across the band,
>>even more so when you look at the spot frequency you stated.
>>ie F/B plus corresponding F/Rear (they should go together)
>>
>>
>> >I made no extraordinary gain, null depth, or bandwidth claims. My
>> >antennas work like most other antennas in the world.
>>
>>Regarding the example that you provided I agree that you did not imply
>>extraordinary features but to focus on one statistic to make a point
>>while ignoring others is good for gottchas but has no place in a
>>serious discussion
>>
>> >
>> > > 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.
>> >
>> >As I understand this, you are saying you have an antenna (with
>> >three reflectors) that meets the goal of being very broadbanded by
>> >virtue of having three reflectors.
>>
>>Yes, that is a correct interpretation except I would not go the
>> extra step by adding " by virtue".
>>
>> >It appears you are saying it has a deep wide rear null (more than
>> >50 dB?) at useful angles, a flat and modest driving impedance
>> >across "the band" (whatever band that is), and as I recall it has
>> >comparable or more gain than other antennas the same physical
>> >size (I believe you mentioned that in a prior post).
>>
>>Yes. In it's basic form that is what I stated tho it came up initially
>>as a response to a poster who focussed on multi reflectors of long physical
>>length My response being that my antenna has three reflectors each
>>with a physical length less than the driven element, but yes
>>I stand by the statement .What are you leading up to?.
>>
>>
>> >Many people would love to have an antenna like that!
>> >
>> >I can't deliver one, it is far beyond my technical skills and meager
>> >understanding of antennas.
>>
>>
>>I don't believe that for one moment Tom!
>>You may take issue as to the value of the priorities taken
>>for such a design which would be a debate of it's own.
>> You have already raised the value of emphasis placed on
>>any rejection figures because of the occurance of "back scatter"
>>Some would prefer to compromise in other areas.(no free lunch)
>>
>>
>> >> 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 ?
>> >
>> >It does everything I expect it to do, which is nearly all it can do
>> >according to theory.
>>
>>Well no one is advocating new break thu's in theory, just a reexamination
>>on how we approach things and a reevaluation of prior sacred cows.
>>A past post talked of selsyns and prop pitch rotators a 50 year old
>>association
>>made before cheap real time cameras were available.
>>The first part of this thread suggested that reflectors were always longer
>>than the driven element and this is not ALWAYS so.
>>
>>Let me get back to the antennas where you imply that the extrordinary
>>skills required
>>are beyond you. I think you are being modest here.
>>
>>In this thread I suggested an antenna that could be termed a combination
>>or interlacing of three antennas. One would be designed for the lower
portion
>>of the band, another for the center and another for the upper portion .
>>When these are interlaced for a single antenna with a single driver on a
>>single
>>boom you have a high density element array with three reflectors.
>> Not really that hard to do, go with the flow Tom and hold off with the"
>>butts."
>>Since you mentioned computor programs it suggests you somewhat embrace
>>the idea and accuracy of simulations.(when done correctly ofcourse)
>>The following computor stats (just the stats maam, just the stats)
>>shows what one should expect from such an aproach
>>
>>Yagi, < 1 WL boom,13 elements 3 of which are reflectors at 65 feet.
>>
>>FREQ GAIN F/B F/B are generally also the 'Worst Case'
>>28.0 15.56 25.6 lobe rejection figures except for
>>28.1 15.67 31.69 portions of the band where F/B really
>>28.2 15.75 37.31 escalates
>>28.3 15.82 42.54 This antenna provides a natural 50 ohm
>>28.4 15.87 47.07 impedance and allows good SWR across
>>28.5 15.92 48.18 the band.
>>28.6 15.93 35.28 Feed line is placed in a metal tube
>>28.7 16.0 44.34 parallel to the boom to prevent near field
>>28.8 16.03 39.46 distortions
>>28.9 16.07 35.81
>>
>> If you compare the above with the Hygain antenna improvement/modification
>>article in the Handbook 17 th edition for a 1 WL boom I think you will agree
>>that my statements are basically correct (no nitpicking !)
>>The antenna pattern is clean with 54 degrees half power with
>>with no side lobes at the front.
>>
>>So that's where I am coming from Tom, It is a bit long but should put the
>>whole thread in context plus figures(meat) to substantiate what I am saying.
>>
>>Best Regards
>>Art Unwin KB9MZ
>>
>>
>> >73, Tom W8JI
>> >w8ji@contesting.com
>> >
>> >--
>> >FAQ on WWW: http://www.contesting.com/FAQ/towertalk
>> >Submissions: towertalk@contesting.com
>> >Administrative requests: towertalk-REQUEST@contesting.com
>> >Problems: owner-towertalk@contesting.com
>> >
>> >
>> >
>>
>>
>>--
>>FAQ on WWW: http://www.contesting.com/FAQ/towertalk
>>Submissions: towertalk@contesting.com
>>Administrative requests: towertalk-REQUEST@contesting.com
>>Problems: owner-towertalk@contesting.com
>
>
>
--
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com