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Author Topic: Lowering SWR on one band of tri-band beam  (Read 782 times)
NZ5N
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« on: June 26, 2013, 12:32:46 PM »

Hi,

I have got an old Cushcraft A4S tribander.  It is working on all 3 bands.  The low SWR point on 10 and 20 is 1.3:1 but on 15 it is 1.8:1.  I had to shorten the driven element from the factory specs by a few inches, apparently because the prior owner had 8" leads extending from a Hy-Gain BN-86 balun, see http://qsl.net/nz5n/Hygain%20balun.jpg (the BN-86 manual says to keep the leads as short as possible to avoid lowering the frequency).  I thought about shortening the leads but the antenna is working quite well as is on 20 and 10 so I decided not to mess with it.

Any thoughts on how to lower the SWR on 15, without messing up 10 and 20?  I'm only able to cover a small portion of 15 before the SWR rises above 2:1.

73, Bill NZ5N     
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WD8KNI
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« Reply #1 on: June 26, 2013, 07:54:53 PM »

You didn't mention what height the beam is mounted at.  As the height goes up and down so does the SWR on each band, not proportional on each band.  I would shorten the leads to specification, reset to beam to factory specifications, and understand what is going on with height?   Make sure you are using the measurements for CW or Phone the portion you choose from the manual.  If you still have problem adjust the portions of the beam that need it for what you want.  Since you said the beam was old, make sure the traps don't have critters inside them..  that is the primary cause of problems..  Fred/wd8kni
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