[TowerTalk] Re: Beverage boxes

[n4kg@juno.com]

Interesting information Tom.

For years, I worked JA's listening on my 400 ft SSE 
unterminated Beverage.  Then I built a bi-directional 525 ft 
antenna and found that it heard as well to the SSE as the 
400 ft Beverage, but I picked up 4 to 6 dB to JA, confirming 
your predictions.

Most of my RX antenna feedlines all run on the ground.  
Does that help minimize pickup?

de Tom  N4KG


On Tue, 19 Sep 2000  "Tom Rauch" <w8ji@contesting.com> writes:
> 
> > I know, the purists will tell me that I am compromising
> > my performance.  Hey, I don't even terminate my Beverages.
> > I still hear plenty of DX on the Beverages that I can't copy
> > on my transmit antennas.  Results?  Only need A5, BS7, P5
> > on 40M,  and only need ~16 countries on 80M.  160 could
> > be better (have 240+ countries). 10 or more acres would help.
> 
> Hi Tom,
> 
> The difference between terminating and not terminating a Beverage 
> has progressively less effect as frequency is increased. That's 
> because ground losses below the antenna and radiation from the 
> antenna tends to "self-terminate" the antenna as it is longer and 
> longer in terms of wavelength.
> 
> With my 500 foot long antennas on 160 meters here, about 30% of 
> the current is lost by the time the far end is reached. That's about 
> 
> half the power, or 3 dB one-way loss. That means the antenna has 
> almost 4 or 5 dB F/B with no termination!
> 
> The longer the antenna in wavelengths, the more the antenna "self-
> terminates" along its length.
> 
> On 160 meters, if noise is primarily coming from the backfire 
> direction, termination can improve S/N ratio by 10 dB or more. If 
> noise is evenly distributed around the antenna termination will 
> improve S/N by a couple dB. If noise primarily comes from the 
> direction of the signal termination will make no difference.
> 
> If you use a poor ground system on the Beverage, such as a few 
> ground rods, the feedline shield can "pump" the ground rod up and 
> down in potential with noise and signals picked up by the feedline 
> shield or conducted along the outside of the shield from the house.
> 
> That's why I use isolation transformers with a two turn primary and 
> five turn secondary on a 73 mix binocular core to feed my 
> Beverages. Autotransformers connect the shield directly to the 
> Beverage ground system, not always a good idea since the 
> feedline can be a big "antenna" when the ground system at the 
> Beverage is less-than-perfect.
> 
> I also use connectors, primarily so I can service the antenna and 
> test the antenna. A shielded box is a waste of time, however. As 
> are "Faraday shields" and sloping feedpoints.
>  
> 
> 73, Tom W8JI
> w8ji@contesting.com
> 
>

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