[Fwd: LF: Multiple Tuned Vertical - Example]

[Andre' Kesteloot]

Soegiono, Gamal wrote:

> Hello all
>
> While compiling an article about the german LW-BC transmitter
> site "Donebach", I come acros some interesting facts about the
> first antenna system which was in use there from 1967 through
> 1970 - a multiple tuned vertical, based on the design principle
> of Ernst F.W. Alexanderson.
>
> Four steel lattice masts, height 200m, cross section 2m by 2m
> are aligned in a star figure. All mast are isolated from ground
> at their bases. Each mast has its individual burried radial
> system consisting of 100 radials 200m each. The radials are
> made of zinc plated steel "tape" (30mm by 3mm approx.) burried
> half a meter below ground level. The total length burried
> calculates as 80km (nowadays system 2*60*360m=43.2 km).
>
> The mast feeding the antenna system is placed in the center of
> a triangle.
> >From center 330m to zero degrees is placed the first,
> >From center 330m to 120 degrees is placed the second,
> >From center 330m to 240 degrees is placed the third periferal mast.
>
> A top load is spun from the central mast to each of the periferal
> masts. Each of the three toploads comprise 10 "wires" spaced by 1m
> making a rectangle 10m by 330m (there is no means to connect one
> periferal mast to the other directly, only via central mast).
>
> Operating frequency that time was 151.0 kHz (1987m WL).
> The base of the central mast is fed by a T-Network
> (base)series L1, shunt C, series L2(coax).
> The bases of the three periferal mast are connected via
> L3 to ground.
>
> The approximate Reactances are:
> X(L1)=j157 Ohms
> X(L2)=j60 Ohms
> X(L3)=j94 Ohms
> X(C)=-j60 Ohms
>
> The head designer of the first Donebach antenna system
> Dr. Heinz Graziadei claimes the efficiency of the antenna
> system to reach 95% (the two mast system in use nowadays is
> said to have an efficiency of 88%).
>
> -----------------------------------------------------
> Hi there down under in ZL:
> -----------------------------------------------------
> It is said that in Paengatoa (New Zealand) we may find
> (if still existing) a 100% copy of the Donebach-1 Antenna System.
> Perhaps you can check that unconfirmed info and take pictures ??
> -----------------------------------------------------
>
> Using a very simplified model (top load modeled by one wire only
> having 2m equivalent diameter, all masts modeled as wires 2m in
> diameter) of the antenna, defining Ground as perfect, wire losses
> as zero (to obtain the radiation resistance only) using a test
> version of ELNEC I get the following numbers:
>
> Rfeedpoint (Rrad) is about 118 Ohms
> current in central mast (base/top) 1.00A/0.62A
> current in all periferal masts (base/top) 1.02A/0.65A
>
> -----------------------------------------------------
> Historical add-on:
> -----------------------------------------------------
> >From 1967-1970 the LW-BC transmitter site Donebach
> (49N39, 09E11) was allowed to use 250 kW transmitter
> (HF output power) and an omnidirectional radiation
> pattern in azimuth on the assigned frequency of 151 kHz.
>
> The Romanian LW-BC station in Brasov (45N43, 25E36) used the same
> frequency with 2000 kW transmitter and omnidirectional
> radiation pattern in azimuth. There are even more stations
> sharing the same allocated frequency but their ground distances
> to Donebach are at least twice as much as in between Donebach and
> Brasov.
>
> The ground distance in between latter sites is about 1300 km
> and was assumed sufficient to provide protection of each stations
> intended coverage area - a false assumption. Receiption of
> Brasov Program in the intended coverage area of Brasov was
> systematically "jammed" by the Donebach Program - WHY ???
>
> The Donebach site is at 510m above sea level, an area of 2 sqkm
> with level variations below 10m. The site, in the middle of the little
> mountain area of "Odenwald", formerely was a marshland. During
> WW2 there was an attempt to install an airfield there. The terrain
> was drained and leveled to some extend. The site nowadays is still
> marshy, i.e. you get wet shoes when walking around, except for
> the hottest summer season. Ground conductivity approximates
> three milliSiemens. There is a virtually unobstacled "free-shot" to
> the horizon in any direction.
>
> I do not have details of the Brasov site, all I heared, the ground
> conductivity is "very bad", perhaps caused by the porous carbon
> type of ground.
>
> The Donebach site therefore has an natural benefit over the
> Brasov site. Rating the excellent Donebach-1 Antenna System
> it is easy to understand, why the 250kW classed Donebach site
> could outperform the 2MW classed site in Brasov in it's
> own coverage area !!
>
> As a temporary countermeasure, Donebach reduced power to 120kW
> and 60kW without much help for the Brasov coverage area. In 1970
> the service in Donebach was stopped (Mainflingen took over temporarily)
> in order to convert the omnidirectional Donebach-1 Antenna System into
> a 2 mast directional antenna system (Donebach-2 Antenna System).
>
> This did not help either, as two of the former masts were re-used at
> their original location, the relative distance (330m) was insufficient to
> provide the required cardioide azimuth pattern with a deep enough
> Null in direction to Brasov.
>
> The final solution was to completely redesign the antenna system
> (went in operation Oct 1982) to what we know today as the
> Donebach-3 Antenna System (see my recent "profile").
> -----------------------------------------------------
>
> 73 de Gamal