[TowerTalk] 160m. Inverted L question

[Ted K2QMF]

Hi Dave,

Do you mean that with the tower tuned to 160
it seems to become a reflector??

Many Thanks for your info on this subject...

73,
Ted  K2QMF

On Wed, 16 Jan 2019 12:04:56 -0700 David Gilbert
<xdavid at cis-broadband.com> writes:
> 
> Pretty much this.  I modeled K9OM's setup for him, and although I 
> couldn't accurately copy his ground conditions and radial field, the 
> 
> model said there was virtually no interaction at all.  He doesn't 
> have a 
> lot of top loading on his 57' tower so that makes qualitative 
> sense.  He 
> is now planning to put his effort into upgrading his radial field 
> and I 
> referred him the N6LF's work on that.
> 
> I was, however, able to significantly distort the model to show a 
> major 
> effect on his pattern, but only by adding enough inductance into the 
> 
> tower to essentially tune it to 160m.  With the right value of 
> inductance the pattern turns cardioid with about a 20 db notch in 
> the 
> direction away from the tower.  That also makes qualitative sense, 
> but 
> I'm not sure that's a typical condition.  A tower that isn't 
> approximately close to resonance shouldn't have any more effect on 
> an 
> adjacent Inverted-L than a 15m element would have for 20m on a 
> tribander.  The fact that the tower is grounded is irrelevant.
> 
> I think hams often like to generalize far too much without bothering 
> to 
> investigate further, especially in the case of antennas.  We have 
> tools 
> available to us now that can turn rules of thumb (at least some of 
> them) 
> into science, but somehow the myths still perpetuate.
> 
> 73,
> Dave   AB7E
> 
> 
> On 1/16/2019 10:43 AM, Rob Atkinson wrote:
> > Where does the idea come from that a grounded tower holding up an
> > inverted L is a problem.  Is this just some notion that took hold?
> > The tower is some how an RF sponge?  Hams have been doing this for
> > decades.  Of course the tower and ground system are bonded to each
> > other so the tower provides a return current path as with a ground
> > system.  How is this different from an AM broadcast skirt fed 
> grounded
> > tower.  I have a 50 foot mast holding my inverted L--the L wire is 
> out
> > about 3 feet from it.  The mast has a 15 foot stinger on top to 
> make
> > it a 1/4 wave 80 m. vertical.  I can ground the mast or float it 
> above
> > ground when using the inverted L on 160 but I see no difference in
> > performance.  Anyone really concerned about this could always drop 
> a
> > second wire on the opposite side from the inverted L, and tie the 
> two
> > together at top and bottom with the single inverted L horizontal 
> wire
> > continuing on, but I doubt if it would make much difference.
> >
> > 73
> >
> > Rob
> > K5UJ
> > _______________________________________________
> >
> >
> >
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> >
> 
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> 
> 
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