[TowerTalk] 160 meter antenna question

[i4jmy@iol.it]

A top loaded vertical is actually a vertical antenna when the function 
of its loading structure is that to only lenghten (electrically) the 
antenna and not to radiate. An inverted L antenna with reasonable 
symilar proportions between the vertical and the horizontal leg doesn't 
differ much by a quarter wavelenght radiator because the top loading 
structure is actually "collapsed" in a single wire and doesn't exactly 
behave like a top loaded antenna. The result of such antenna type is 
infact a current distribution that's still quite resembling that of a 
linear radiator and leads a certain part of the horizontal (slant) 
portion to radiate significantely.
Since horizontal and vertical polarized fields "live" their own 
separate lifes, from the transmitting point the horizontal portion of 
the antenna doesn't contribute anyway much in any case to the radiated 
field at low angles, radiationd that stay a matter of the vertical 
portion. While receiving, instead, the story is different because the 
high angle signals, whose the horizontal wire responds well, add to the 
others on the way to the receiver and may hide what's a "low angle" but 
not strong enough to "win" over.
Concerning what's to use as loading device, best is always capacitive 
and becomes the only possibility when the required amount of loading is 
big and efficiency must be good.
If the required loading is small, then a coil can be placed anywere 
(i.e. confortably at base, may be integrated as a part of a step up 
impedance autotransformer)without affecting much the overall efficiency.
When the loading amount is big, anywere the coil is placed there's no 
real way to minimize its losses.
When the loading is neither big or small, the best approach is to load 
capacitively as much as it is possible and to leave the coil the 
function of cancelling the residual reactance and resonate the 
antenna.   

73,
Mauri I4JMY
> ---------- Initial message -----------
> 
> From    : owner-towertalk@contesting.com
> To    
ontesting.com>, "Tom K Osborne" <w7why@juno.com>
> Cc      : 
> Date    : Mon, 5 Jun 2000 08:26:21 -0500
> Subject : Re: [TowerTalk] 160 meter antenna question
> 
> 
> Actually when installed over many 1/4 wave long radials, there is not 
much
> improvement beyond a 1/8 wave radiator(70 ft or so). How you top load 
it is
> of little importance as long as the current node remains at the 
bottom of
> the antenna. I would prefer to use a top coil and single top wire for
> simplicity. As far as "balancing" the top hat, I don't know it it 
would
> improve the pattern or not. My gut feeling is that there is so little
> current in it, that it won't matter much ( not scientific ).
> 
> Geo>K0FF
> -----Original Message-----
> From: Tom K Osborne <w7why@juno.com>
> To: towertalk@contesting.com <towertalk@contesting.com>
> Date: Sunday, June 04, 2000 7:15 PM
> Subject: [TowerTalk] 160 meter antenna question
> 
> 
> >
> >
> >Hi TT'ians
> >
> >What is the difference between a 90 foot vertical with 35 foot
> >horizontal wire (inverted "L") and a 90 foot vertical with 4 35
> >foot wires (top loaded vertical)?  Will either of them work
> >better than the other?  TIA and 73
> >Tom W7WHY




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