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Re: [TowerTalk] Dipole fed with balanced line?

To: Ken <>
Subject: Re: [TowerTalk] Dipole fed with balanced line?
From: Jim Lux <>
Date: Tue, 17 Jan 2012 07:47:57 -0800
List-post: <">>
On 1/17/12 7:35 AM, Ken wrote:
> On Jan 17, 2012, at 9:35 AM, Jim Lux wrote:
>> No, but you could do it by having a very low loss matching network and a
>> physically small radiator.
> You are trying to tell me that if I had an excellent matching network, I 
> could use a 2m dipole on 80m and it would be just as effective?
> Sorry, I think you are confusing feed and matching losses and ignoring an 
> effective radiator.  There is no way that I will believe that a "physically 
> small radiator with a very low loss matching network" is as effective as a 
> half wave antenna.

What does "effective" mean?
If you define it as "getting RF power at the feedpoint launched into 
space", ANY size lossless antenna works pretty much the same.  That are 
differences in the spatial distribution of the energy: some antennas are 
more directional than others.

So, yes, theoretically, you could use a 2m dipole on 80m.  However, you 
cannot do this "practically" because the excellent matching network you 
would need cannot be built with actual materials.

There are some fundamental limits on antennas which relate size, 
directivity, and stored energy in the antenna.

The challenge of antenna design, in the real world, is choosing which 
components to use and what compromises to accept.  Do you go with end 
loading of some sort which changes the current distribution in the 
shortened antenna, and so changes the pattern slightly, and makes the 
feedpoint impedance a little less annoying to match, at the expense and 
hassle of the end load itself?  Do you use multiple L/C in a matching 
network to get low loss and good match in multiple bands, or do you use 
multiple elements like in a fan dipole.

For a not too short dipole (say, >75% of normal length), the added 
losses in antenna and matching network won't be very big.  And 
pattern-wise, there's almost no difference between the 75% length dipole 
and the full size.


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