To: <towertalk@contesting.com>
>Date: Wed, 07 Feb 2001 20:23:06 -0500
>To: art unwin <aunwin@fgi.net>
>From: Joe Reisert <jreisert@jlc.net>
>Subject: Re: [TowerTalk] Re: Yagi's
>
>Hi Art,
>
>Thanks for the AO file on your antenna. I decided to see what you had for
>your Super Yagi. I put your file into the AOP program by K6STI. It took
>time to get it running but fixed those problems quickly.
>
>I originally thought the extra reflectors you were using were off axis but
>I now see from the view plot they are on the same boom just further behind
>the first reflector.
>
>Here are my first observations on your antenna. The pattern is superb as
>you said. My programs says the gain is 15.42 dBi (yes I know what DBi's
>and dBd's are and the difference!). I prefer to use dBi as I do EME
>designs. On my AOP program the entire rear (90-270 degrees) is at least 45
>dB down. I doubt you'd hear any weak signals of the rear! It reminds me of
>some of the techniques used by K6STI. He has published some incredibly
>clean designs. However, many of Brian's designs are narrow band and often
>have very low impedances (less than 20 Ohms). I measured your impedance at
>23.3 +j 3.3 Ohms.
>
>Next, I decided to look at some of my own 50 Ohm direct fed Yagi designs
>and found a 6 element design that has a 1.0 wavelength boom like yours so
>it was a good one to do a quick comparison on performance. It has a single
>reflector and 4 directors. The gain is about 11.5 dBi in free space.
>Although I didn't test your design in free space, I estimate it's about 10
>dBi or so under the same conditions, about 1-1.5 dB less gain than my
>simple 6 element design.
>
>Then I tried to see what would happen to your design if the rear 2
>reflectors were removed. This would show how much, if any, the extra
>reflectors helped. The gain and impedance were almost exactly the same but
>the rear lobes were now just over 30 dB below the main beam. Still not to
>shabby.
>
>Without any optimization, I set up my simple 6-element Yagi with a direct
>50 Ohm feed at the same height of your antenna. Remember, this antenna was
>really not fully optimized and was only designed in free space.
>Regardless, it had a gain of about 16.57 dBi, over 1.2 dB more than your
>design. However, the rear lobes were about 25-30 dB down, but still not
>too shabby!
>
>As a quick summary, the design you have proposed is quite unique but it
>requires LOTS of aluminum, over twice that of my simple 6-element Yagi.
>While your design has an excellent front-to-rear (90-270 degrees) pattern,
>that comes at a cost in gain of over 1.0 dB from the much simpler design
>which still has a respectable front-to-rear ratio.
>
>73,
>
>Joe, W1JR
>:
>>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
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>> >> >
>> >> >
>> >> >
>> >>
>> >>
>> >>--
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>> >>Submissions: towertalk@contesting.com
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>> >
>> >
>> >
>>
>>
>>--
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