[TowerTalk] lightning bolt quads
k2xx at swva.net
Thu Apr 20 19:43:17 EDT 2006
Lew McCoy also reported on the 10/20M interaction in a CQ product review
article on the LB quad about 10 years ago. Based on my personal
experience, separate feedlines with 1/4 wave links between the driven
elements and the switch terminals are the best way to go.
FWIW, I modeled and constructed a two element, two band quad for
30/40M. The feed impedances were indeed around 100 ohms, but I
deliberately was aiming for that impedance in the model so I could use
1/4 wavelength 72 ohm matching sections to match 50 ohm feedline.
Jim Jarvis wrote:
>Like Jim, below, I also asked Mike at Lightning Bolt about the
>feed system, and got a similar response.
>However, there MUST be an interaction between the 10 and 20m
>elements. A 2 wave loop emits in exactly the opposite fashion
>as a 1 wavelength loop. The result is that the 20m element fills
>in nulls on 10. What tends to limit that effect is that the 20m element
>is seriously mismatched, so very little actual current flows in it.
>Mike denied that this was even a factor. Cebik says it is.
>I was seriously considering separate feeds for my 2 el lightning bolt,
>fed with 1/4w lines to a central switch. (don't forget to use ferrites
>to decouple the feedlines from switch common). Upon further consideration,
>I donated the antenna to the red cross and bought an lpda.
>Incidentally, I also had the 4 el. add-on kit. It's a monster antenna,
>which I am quite sure plays extremely well. Remember how big it is,
>when planning the tower site. Trees can be a problem.
>Date: Thu, 20 Apr 2006 06:43:26 -0500
>From: Jim Rhodes <k0xu at iowadsl.net>
>Subject: Re: [TowerTalk] Lightning Bolt Quad
>To: "denis coolican" <coolican at telus.net>, <towertalk at contesting.com>
>Message-ID: <188.8.131.52.0.20060420063739.01f7aef0 at iowadsl.net>
>Content-Type: text/plain; charset="us-ascii"; format=flowed
>I asked the Lightning Bolt guy about that once and he got very
>defensive about his feed system. Said the tuning would be all off and
>he wouldn't be responsible. Others have said the opposite, that
>quarter wave lengths to a switch were needed. I am sure there are
>many opinions on this.
>At 12:02 AM 4/20/2006, denis coolican wrote:
>>This four element Lightning Bolt Quad covers 20, 17, 15, 12 and 10
>>meters. It is fed by a common balum. (one input PL259 and 5 output
>>pairs of conductors)
>>Does anyone know what type of balum this is and what would be the
>>replacement for it?
>>I imagine the driven elements for each band has an impedance of
>>about 80 to 100 ohms. The feed into the balum is 50 ohms.
>>If a person provides a 2:1 balum for each feed, would the unused
>>balums be terminated in 50 ohms or left open?
>>Any more thoughts on this antenna?
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