I think this is a wording issue. We all understand the difference between VF in the transmission line and VF in free space. What caused difficulty was the term "arriving at". I took this to mean "at the antenna" not free space, as there's no need to mention the antenna if the desired meaning was "free space". Chuck
> From: [email protected] > To: [email protected]; [email protected]; [email protected] > Subject: Re: Topband: BOG question > Date: Thu, 1 Oct 2015 18:57:09 -0400 > > > I believe there is a large influence of height above ground on VF. > > From a theoretical basis, this has been "known" since Wise's classic paper > > "Propagation Of High Frequency Currents In Ground Return Circuits" (1934). > > This was experimentally verified in the Litva and Rook report from the CRC > > (Canada), and compared with theoretical results. > > These guys didn't extend their calculations to right-on-the-ground > > antennas. The attached (if it gets through the server) is from a > > spreadsheet of mine based on the Wise equations. The influence of height > > on VF is very very pronounced. > > Chuck > > Frank is absolutely correct in what he said. > > The velocity factor decrease in the Beverage has nothing to do with the > arriving wave velocity that affects the required phasing spacing. The wire > looks longer because the earth slows the wave ***in the wire's transmission > line mode***. The required spacing and stagger is set by the wave, not the > wire. It is the same in a BOG, a normal Beverage, or in a vertical. > > The broadside spacing, to increase directivity a useful amount, has to be up > around 1/2 wave or more. The end-fire or echelon spacing has to be the same > as a normal Beverage, or vertical, to have useful directivity increase. > > The only thing the earth does is slow the velocity in the transmission line > formed by the wire and earth image. The antenna cannot be a long as a > regular Beverage because of the slowed propagation in that "transmission > line". It is little different than loading the wire with any lossy > dielectric. > > While the antenna is limited to less length because of velocity factor in > the wire's transmission line mode, the fact it is a BOG has no bearing on > the wave velocity, or the required spacing or stagger. > > 73 Tom > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
