Date: Mon, 25 May 2009 15:57:00 +0200
From: "Dennis" <Dennis.Hennig@gmx.de>
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Subject: Re: LF: Re: Re: First Portable Trip
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Hi Richard!

I'm interested in Your /p antenna discussion :)

> 1) T antenna. Am I right in thinking that in the classical T 
> configuration, the horizontal part of the aerial is only there to add 
> capacity - i.e. it makes no contribution to the groundwave? If so, I 
> assume that I can use very thin wire for the T?

Well, as far as I understand antennas, the horizontal wires are part of the electrical length of the antenna. There will be current flowing into these horizontal branches, hence in any case losses will occour there. Another question is of course: How big these losses are, and if the additional losses are better, than not climbing your hill due to a too-heavy antenna?

>From the "meeting point" of the vertical and horizontal parts, the horizontal currents are fed into opposite directions, so if both horizontal wires are exactly the same length, height, over similar ground, no houses and other wiring disturbing the fields, ... , (lets call it "free space" like antenna books do ;)  ) , the radiation of the horizontal parts cancel out each other at some distance, pure vertical polarization remaining.


> 
> 2) In the more likely configuration with "horizontal" wires actually 
> acting as an inverted V can I still use very thin wire without reducing 
> performance?
Anyone with simulation capabilities out there?
Remember, that as others just said, sloping horizontal parts do reduce the effective antenna height and decrease efficiency. So 4 (or 6) shorter wires may act better than 2 longer wires.


> 3) Is there any benefit to be gained by having an inductor at the top of 
> the vertical section of the T? 
I've read somethere: Yes it is, because lower current -> lower losses, even though the coil has to be bigger (may be mechanical problem?)

> If so, will the loss of the inductor be 
> relevant if the part of the antenna above it (the T wires) don't 
> contribute to useful radiation?
Yes, relevant. Again, although horizontal polarization cancels out at least "in free space", there is current flowing up there. 
> 


73
Dennis 
DL6NVC
Berlin





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