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Author Topic: 70cm Beam  (Read 3593 times)
KB3EGW
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Posts: 2




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« on: December 24, 2000, 12:55:04 PM »

I am trying to find plans to build a simple 70cm beam.  I want to mount it below my Cushcraft 13B2.  Does anyone know if it is possible to modify the Radioshack FM antenna design to do 70cm instead of 2m, and if so how?
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WB6BYU
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Posts: 13482




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« Reply #1 on: January 02, 2001, 01:03:16 PM »

I recommend the "Quagi" designs by K6YNB (now N6NB) which
appear in the ARRL antenna books and perhaps the Handbook.
These are a good combination of good performance and ease of
construction.
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WB2WIK
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Posts: 20636




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« Reply #2 on: February 02, 2001, 05:54:32 PM »

Sorry for such a delayed response, just spotted your query.  If it's not too late to be helpful: The R-S TV antennas are not worth modifying for 70cm.  Just about everything that could possibly be wrong, is wrong, and it would be faster and easier to start from scratch.  The N6NB Quagi designs cited by Dale earlier are totally excellent, cheap, lightweight and very easy to build.  Although Wayne shows plexiglas and shaved 1x2" pine for suitable boom material, bamboo works great also (anything strong, straight and non-conductive) for the 70cm Quagi.  One of the great advantages of this design is it has no matching section to create mistuning or loss; it uses a 1-wavelength (approx) directly-fed wire loop as the driven element, period.  No other parts involved in the feed system, which is perfect for 70cm, where nearly all materials begin to get lossy.  If you build the 70cm Quagi, it might get you excited enough to want to build the 8 element 144 MHz version as well.  Properly built and adjusted, that 8 element design has more gain, and a cleaner pattern, than the Cushcraft 13B2 -- all while weighing less and being much less likely to become detuned by weather!  Good luck & have fun.
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