Topband: Folded Marconi Antenna

[Herb Schoenbohm]

Kevin Nathan wrote:

>I would then go out an electrical quarter wave calculated for the particular type of line I was using and would tie the two sides together.  I would then tie the far end together so that the short section of twin lead tied together at either end acted as a voltage cap.
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>I have tried to find descriptions of this antenna on the internet without much success.  I find the antenna but they don't mention where to tie the ends together and one description actually says that if you put it up as an inverted L, you actually need to make it shorter but it doesn't give any idea of how much shorter it ought to be. 
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>Kevin,
>

A version of the folded back marconic top exists in a US Military 
handbook but with only the far end tied together.  The total length of 
the flat top (with one end of the two wires connected and a single 
connection to the vertical downlead on the other end is 1/8 wave because 
the total distance traveled is a 1/4 wave on the top section alone.  450 
ohm ladder line is actually better than twin lead as the top section 
since the voltages are quite high at the open ended portion.  The 
military version uses open wire line with spacers but there is no 
reason, depending on power levels why  ladder line would not work.  This 
portion of the antena is d3eisng to cancel radiation from the flat top 
concentrate more  radiation on the vertical portion. This will actually 
benifit your lower angle take off for working DX on topband and 80 
meters,depending on the design frequency.

Good Luck


Herb Schoenbohm, KV4FZ

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