A 6 Meter Antenna
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VK4ZJB
A 6 Meter Antenna
Possibly I hope to obtain some clarification here, without "buying an argument". Re a 6 meter 5 element hairpin matched yagi described in a respected American publication: Not wishing to be involved with the theoretical aspect of the "Hairpin" conjugate reactances, etc which are easily normalised using negative numbers, and a Smith's Chart, I seem baffled by the following: This "yagi" by inherent design, now has a "Director", as well as reflector (Of course LONGER than the driven element.) the REFLECTOR, that is...Several VK4's have constructed this unit, all to encounter great difficulty getting the VSWR below 1.4 if that. How can this design work with an effective reflector in FRONT of the d.E.? Also, during another discussion along the same lines, I Was swamped with the reply "It worked for me"---so will a dipole in ANY respectable Es session. Sensible comments sought please, of the technical aspect, and/or personal experience. No, I never constructed one. I had a bad enough let down, (along with the same comments from ZL) with a 6m LPY but different publisher. The old 5/5 from the same source, albeit 1972, got well over DXCC here on 6---You DON'T need to assume you cannot find good yagis described, but hairpin match---no thanks. 73 John VK4ZJB.
Re: A 6 Meter Antenna
John,
Yagi design has come a long way in the last 30 years.
Have a look at these web sites for some newer designs:
http://www.yu7ef.com/
http://www.qsl.net/d/dk7zb//start1.htm
http://www.g0ksc.co.uk/
At 5 elements, you could even use the classic DL6WU designs, using the software from VK5DJ:
http://www.vk5dj.com/
You can then build it with the material that you can obtain. And most of the computer optimised designs are not a lot different in gain, but some claim cleaner patterns with lower side & rear lobes.
Also look for the DJ9BV 6 element design that was in DUBUS some time ago. I built one of them, and it worked fine until I took it down. Boom length is 6 m.
There lots of other hits on the net, but the above seem to be reproducible.
Good luck,
Peter VK3PF
Yagi design has come a long way in the last 30 years.
Have a look at these web sites for some newer designs:
http://www.yu7ef.com/
http://www.qsl.net/d/dk7zb//start1.htm
http://www.g0ksc.co.uk/
At 5 elements, you could even use the classic DL6WU designs, using the software from VK5DJ:
http://www.vk5dj.com/
You can then build it with the material that you can obtain. And most of the computer optimised designs are not a lot different in gain, but some claim cleaner patterns with lower side & rear lobes.
Also look for the DJ9BV 6 element design that was in DUBUS some time ago. I built one of them, and it worked fine until I took it down. Boom length is 6 m.
There lots of other hits on the net, but the above seem to be reproducible.
Good luck,
Peter VK3PF
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VK4ZJB
Re: A 6 Meter Antenna
Tnx Peter, It's just that such a monumental disaster "got through the works" hi, best wishes, John. 
Re: A 6 Meter Antenna
John,
These days, I always plug the dimensions into EZNEC and look at the likely gain, impedance and pattern shape - firstly in free space, and then at the planned height above ground. You should get a good feel for the expected performance of the antenna. EZNEC is easy to use (see the recent article in AR) and there is a free version which should work fine for a single Yagi http://www.eznec.com/.
Yes, there are lots of people out there making claims about antennas and publishing/republishing old designs without having investigated the antennas critically.
Another useful source of information are the LB Cebik (SK) pages http://www.cebik.com/. If you have not done so, you will need to register (free) - it takes a couple of steps and waiting for email confirmations. The look for the "Tales and Technicals: A Little History and a Lot of Antennas" link once logged in. There is limited material specifically in 6 m Yagis, but it is easy to scale from 10 m or 2 m, especially when using EZNEC.
Good luck.
Peter VK3PF
These days, I always plug the dimensions into EZNEC and look at the likely gain, impedance and pattern shape - firstly in free space, and then at the planned height above ground. You should get a good feel for the expected performance of the antenna. EZNEC is easy to use (see the recent article in AR) and there is a free version which should work fine for a single Yagi http://www.eznec.com/.
Yes, there are lots of people out there making claims about antennas and publishing/republishing old designs without having investigated the antennas critically.
Another useful source of information are the LB Cebik (SK) pages http://www.cebik.com/. If you have not done so, you will need to register (free) - it takes a couple of steps and waiting for email confirmations. The look for the "Tales and Technicals: A Little History and a Lot of Antennas" link once logged in. There is limited material specifically in 6 m Yagis, but it is easy to scale from 10 m or 2 m, especially when using EZNEC.
Good luck.
Peter VK3PF
Re: A 6 Meter Antenna
Hi John
I built such a yagi Jan last year and had a similar battle to achieve a match. The answer was to make the DE a bit longer (I tapped out the ends and fitted a SS bolt giving about 10-15mm more length each end.
The next trick was much more inductance so I attached 2 parallel wires about a foot long at the feedpoint and a slider made from 2 terminals from a chock block bridged with a copper strap. Moved the slider up and down and when fairly well out got a perfect match
I think the DE was designed short to look quite capacitive at the feed point and the bigger L made it work. The original hairpin didnt make it for me.
Good luck, Terry ZL4TAE
I built such a yagi Jan last year and had a similar battle to achieve a match. The answer was to make the DE a bit longer (I tapped out the ends and fitted a SS bolt giving about 10-15mm more length each end.
The next trick was much more inductance so I attached 2 parallel wires about a foot long at the feedpoint and a slider made from 2 terminals from a chock block bridged with a copper strap. Moved the slider up and down and when fairly well out got a perfect match
I think the DE was designed short to look quite capacitive at the feed point and the bigger L made it work. The original hairpin didnt make it for me.
Good luck, Terry ZL4TAE
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VK4ZJB
Re: A 6 Meter Antenna
Thanks for the reply Terry--- no I don't intend making one, just that a few mates had your dramas---the gamma match with a 30.0 Pf doorknob (NPO) and the gamma section adjusted gives a flat VSWR every time---the figure quoted as 7 Pf per meter of wavelength for the gamma cap is out too---5 Pf is spot on. It's a great general reading book, but when they make a boo-boo it can be a beauty---I still don't understand how that yagi can work (It doesn't) with a first director LONGER than the D.E.---Still it is but one of their reinventions of the wheel, hi. As said, their 1972 5 Ele. gamma works a treat.---However now I'm buying an argument, hi. Thanks again for yout input, Terry, Much Appreciated. Best Wishes, John.