Topband: re 2 wire BOG antenna update

[Charles Moizeau]

Bruce,
"...in my area, the most stable earth moisture is at grass/vegetation root level..."

Are you are in fact saying that to be "stable", that is to say, remain the same day in, day out, a "BOG" needs to be evenly sunk to about not more than one inch below the perceived surface?

73,

Charles, W2SH
 

> From: k1fz at myfairpoint.net
> To: k2av.guy at gmail.com; topband at contesting.com
> Date: Mon, 9 May 2016 23:27:24 -0400
> Subject: Topband: re  2 wire BOG antenna update
> 
>  
> A  measurement of My 2 wire directional BOG antenna,  with  calculations for measuring over shoulder high dense thorn bushes in two places, came in at 176 feet
> I could see the wire atop soil level a few places  to stay on track  along the way. 
>  
> Optimum length will vary from location to location with earth conductivity, moisture content. 
>  
> I have a  more simplistic view of the BOG process.  The velocity factor drops as the wire comes in contact with more damp/wet earth. Earth being the other half of 
> capacity to the wire.    I am finding, in my area, the most stable earth moisture is at grass/vegetation root level. 
>  
> Stability is important as the great front to back pattern is only at its resonant frequency. 
> If anyone has missed IV3PRK's research at HC1PF please go to my bogantennanotes, and.see the IV3PRK links...... .my page address is below 
>  
>  
> We need to stop thinking "Beverage" when we talk about 'this' antenna. Any ideas for a name change?
>  
>  
> 73
> Bruce-K1FZ
> http://www.qsl.net/k1fz/bogantennanotes/index.html
>  
>  
>  
> 
>       The pattern is essentially under the influence of several items: 1) the
> electrical length [physical length times velocity factor (VF)], 2)
> interference between the speed of incoming RF in the air and the speed of
> already received RF on the beverage wire and 3) the proximity loss of the
> earth moving the antenna toward a self-terminating behavior. 
> 
> In a regular beverage, the VF of a beverage over deer antler height is .95
> or higher. This "normal" beverage plays based on its *electrical* length,
> just as does one buried or laying on the ground, but it's fairly constant
> and that small reduction in the VF is already in the beverage design
> length. 
> 
> So it's not so much that the design changes as ground is closer, the
> constant *physical* length no longer produces the beverage's design
> *electrical* length. 
> 
> Once you get within a few inches of the ground, the VF starts to decrease
> massively. This reduction continues until the wire is buried. Since this VF
> has been measured from 0.45 to 0.8 in various circumstances, a design
> length for 6 feet in the air will be cut in half by the time the wire is
> buried. Then the difference in speed of incoming RF and RF on the wire to
> the feedpoint will produce effects not in play on a regular beverage. 
> 
> At this point the antenna needs to be accurately modeled in order to
> evaluate the changes in effect. Effective termination resistance is now the
> self-termination resistance plus the physical end termination resistance. 
> Plus, modeling demonstrates that some improvement can be made with simple
> grounding of the far end, or even no termination at all. These last two
> indicate that the standard beverage procedure of terminating for least SWR
> looking into the wire no longer produces best pattern. It really ain't a
> beverage at all in these circumstances. Assuming it still is a beverage and
> caluculating accordingly often produces the "doesn't work worth a d*mn"
> outcome. The antenna must be designed for ground low velocity factor
> conditions. 
> 
> Once very close to, or on, or buried in the ground, ground moisture changes
> will vary performance. Those who have put BOGs down in the woods discover
> that an accumulating layer of wet, rotting leaves over the wire, often to
> four or six inches of leaf layer on top can completely detune what used to
> be a decently performing BOG, rendering it nearly deaf. Woods BOGs need to
> be laid on top of the leaves, and pulled up out of the leaves from time to
> time during the contest season. 
> 
> Lawn BOGs should be lightly buried to start with, dropping the wire into a
> blade cut just barely into the dirt, and the lawn over top kept mowed. Even
> then, the wire needs to be checked annually for *electrical* length when
> the soil is damp and the wire length adjusted as needed. For this it's
> useful to retain a center connection, which is shorted and weather-proofed
> for normal operation. 
> 
> BOGs are cranky RX antennas in the best of times, and one needs to
> disconnect from Beverage thinking when dealing with them. 
> 
> 73, Guy K2AV
> 
> _________________
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