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[TowerTalk] low band receiving antennas options

 To: [TowerTalk] low band receiving antennas options W8JI@contesting.com (Tom Rauch) Mon, 14 Jan 2002 06:45:24 -0500
 ```Hi Rick, > bands. Now if I did my math right this works out to about 301 ft which > I understand is considered a short Beverage and short Beverages don't > work well. Now I think I could get 2 of these short Beverages in Cone of silence lengths have little advantage for receiving S/N over other lengths, unless you happen to have noise that is concentrated in the null area. Odds are you will never know the difference if you use those lengths or not. Short Beverages are sometimes better than nothing, but to offer substantial performance improvements they MUST be terminated and they must be somewhat close to 1 wl long or longer **electrical*** length. The electrical length is ALWAYS longer than the physical length in wavelengths. At my QTH, the velocity factor of Beverages is about .9 or less, so a 500 foot Beverage looks 500/.9 or 555 feet long or slightly longer electrically. You can see detailed discussion of how directivity influences receiving on my web page, www.w8ji.com > behind the house running NE/SW and NW/SE If I made them bi-directional > I would be covering most of the DX areas from my QTH ( TX). I hope you mean reversible, and not bi-directional! You give up around 3 dB of S/N ratio with an unterminated beverage if noise is evenly distributed around the antenna on a shorter Beverage, and more if the noise comes from what would have been a null. In addition, they never receive as well off the feedpoint end even if you do not terminate them. Beverages tend to "self-terminate" because of losses in the antenna and earth below the antenna, so there is always some F/B even when unterminated. > Is this a bad idea? Would I be better putting up a K9AY loop? K9AY loops function as two short phased verticals, except there is some additional response at high angles from the horizontal component of the sloped wires. Because two phased verticals aren't all that directive other than a deep null off the back, they (and other antennas like the K9AY loop) have limited signal-to-noise advantage. The exception is when unwanted signals or noise primarily comes from the null area. Of course if that is all the room someone has, any directivity is better than none! Because of the limited directivity of a Flag, EWE, Pennant, or K9AY loop, even a modest length Beverage is generally much better. You can model it using the guidelines on my web page for determining receiving directivity factor if you have Eznec for Windows, or another program that calculates average gain. > Since I own the land they will be on and it is not being used for > anything I could leave these up year round. I haven't yet gone out > there and measured the area yet but looking at the map that came with > my deed it looks do able if I slant them across the property but not > actually having them cross each other. It does NOT hurt to have Beverages cross, as long as they are separated by a few feet near the crossing point. It does hurt to have the ends near each other. By the way, there is no need to slope the ends downward as some suggest. Sloping the ends does nothing to reduce vertical pickup, if it did the K9AY loop and Flag antennas would not work! You also might use the Binocular cores I suggest on my Web page. It only takes SEVEN turns of wire to make a good transformer, not 20 or 30 like the wrong type of core requires. With the correct core the transformers work better and are much easier to wind. 73, Tom W8JI W8JI@contesting.com ________________________________________________________________________ Where do you get ICE bandpass filters & beverage matching boxes? The same place that pays for the hosting of this list: The eHam Store. Order online at http://store.eham.net. ----------------------------------------------------------------------- ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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