[TowerTalk] [800 M longwire] Basic question...

[K4SAV]

Is it "written" someplace that he has to use the entire span for the active
antenna???


No, but I have already tried reducing wire length to see if this was a 
possiblity.  A shorter wire results in less lobes which does make the 
antenna less frequency sensitive, but it reduces the gain in the lobes.  
Like so many other things in antenna design, it is difficult to find a 
free lunch.  There may be some other things, like you mentioned, extra 
wires etc, that will make a difference, but I haven't investigated any 
of those yet.

Increasing antenna height will also make the antenna less frequency 
sensitive, as well as increase the gain by a large amount, but 
mechanical considerations limit this.

Note: Some of these nulls tend to get filled in, because of 
nonlinearities of the surroundings, but they do so by subtracting some 
gain from the lobes.

Actually, placing a verticle over salt water will produce significantly 
more gain, plus have a predictable pattern, compared to building this 
antenna with 17 gauge wire at low height.  A vertical over salt water is 
a dynamite antenna and hard to beat. .. except maybe by TWO verticals 
over salt water. 

Jerry, K4SAV


Bgsalesmel at cs.com wrote:

>Message: 7
>Date: Thu, 13 Oct 2005 10:54:17 -0500
>From: K4SAV <RadioIR at charter.net>
>Subject: Re: [TowerTalk] Wire Size for 800 meter longwire
>To: towertalk at contesting.com
>Message-ID: <434E8329.4010704 at charter.net>
>Content-Type: text/plain; charset=us-ascii; format=flowed
>
><snip>
>The pattern formed by a long wire is very complex. There are large 
>numbers of lobes and nulls, both in the azimuth and elevation 
>directions. Most of these are very narrow. Because of this any small 
>phase change in the current, causes large changes in the pattern. 
>
><snip>
>
>Jerry, K4SAV 
>
><< My question >>
>
>The QTH has Available a 800M run over saltwater...great.
>He is limited as to "what" he can hang due to mechanics...awww shucks.
>The "far end" is on another's land/fence post - can't be fed from there, 
>right?
>The "pull" measured in pounds is only calculated at 500# or less, with 
>variables...
>
>IS it "written" someplace that he has to use the entire span for the active 
>antenna???
>
>Everyone is bemoning this pattern variable at this length...vs frec, dia, 
>etc.
>I seem to recall something from an old ARRL Ant book about "5 wave/frec 
>lenth"...
>
>Why not consider using one of those "fat" (strong?) guy insulators to adjust 
>the active length near the mid point "FROM" the far end? Should yield 
>something like a sloper fired from the high end I would think...maybe even play with 
>some sort of balast or top loading done "onshore", or short hanging "tail" at 
>the midpoint...computer models should show whatever this could yield, pro 
>and/or con. I'm thinking of some sort of "vertical" component effect here. Maybe 
>even use another insulator on the "near/fired" end to displace the active length 
>more "over water"?? The attachment line could be used as a messenger line for 
>the feed source, eh? OR, it might model better with a free "drooping" 
>feedline config? I think he said he had about 70ft of height to work with 
>onshore...don't know "what" is downslope from his anchor point...maybe a cliff? 
>
>The mechanics then just become an engineering and materials function.... :-(
>
>Just some different thoughts for an already interesting thread... 73 to all.
>
>Mel Frost KD7DCR
>Coeur d'Alene, ID
>
>  
>