[TowerTalk] 160 question from new antenna

[ersmar@comcast.net]

Peter:

     If that alleged null towards Europe is the only thing keeping you from installing the L for the upcoming contest - fuggedaboudid.  The null is really only a 1-2 dB drop in gain in the direction of the horizontal flattop (that is, 1-2 dB more gain AWAY from the direction of the horizontal wire.)  And that's theoretical as seen in modeling with NEC, etc.  I defy anyone actually to measure this bit of directionality in a practical L for Topband.  

     Put up the L (five feet off the tower) along with a couple of on-ground radials, get on the band for the 'test and have fun.  We can help you with the shunt feed afterwards.  

73 de
Gene Smar  AD3F


 -------------- Original message ----------------------
From: "Peter Dougherty (W2IRT)" <w2irt at comcast.net>
> At 09:03 27-12-05, Bill Coleman wrote:
> 
> >How much power do you run? If you only run 100 watts, you don't need
> >the vacuum-variable caps. Even if you are QRO, you might be able to
> >use caps with a reasonable spacing. It all depends on the voltages
> >and currents that are present in the matching network.
> 
> Right now I'm running 600W, but will hopefully go to a little over a 
> kW, and I would like to run legal-limit when funds allow.
> 
> >A shunt-feed is like a gamma match to the tower. Like a gamma match,
> >the difference in diameter between the shunt wire and the tower, as
> >well as the length and spacing of the arm determines an impedance
> >transformation.
> >
> >Now, if you could compute all the parameters of your tower and shunt
> >arm, you could figure out the exact length, and spacing to make a
> >perfect match (or one that you'd only need a little series
> >capacitance). Doing so is quite difficult. Figuring this out by trial
> >would mean a lot of tower climbs.
> 
> Wow...lots of information to digest here in the last couple of days, 
> and honestly it's a bit much for this relative-newbie to digest 
> <grin>. I'm wondering if anybody on T-T in the NYC tri-state region 
> has loaded a tower up and wouldn't object a friendly visit from a 
> curious newbie? I'd love to actually see this done with the ol' 
> Mark-1 eyeball to get a real feel of what's involved. Diagrams and 
> descriptions only go so far. I'm in northern NJ and would be glad to 
> take a drive to see how this is supposed to look :-). Donuts happily provided!
> 
> For that matter, anybody who does this kind of thing professionally, 
> I'd love to explore that option by e-mail as well since I'm not 
> really able to climb (no gear or expertise -- at least none yet!).
> 
> I'm hoping to get something working before the big 160 contest, but 
> at this point, I think I may be looking at next season. I'm very keen 
> on the idea of loading the tower for both 80 and 160, getting a 
> K9AY-style loop running for receive and maybe a separate 40m vertical 
> as well. I like the idea of an inverted-L, but the way my property is 
> configured the only way I could make this work would result in a null 
> to Europe (horizontal-bit of it running northeast), so that's 
> probably not the best option.
> 
> Again, my profound thanks to one and all who replied to this thread. 
> Your assistance is tremendously appreciated. Best of 2006 to one and all.
> 
> 
> 
> - Peter
> 
> W2IRT
> 
> _______________________________________________
> 
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