[TowerTalk] Element loading methods

[W8JI@aol.com]

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Hi Dave,

MCI is still not working after days of trouble with e-mail!! This is a AOL
repost,which always  seems to work properly.

> The question for the group is how much better is linear loading, traps,
> or center loading
> both ends of an element over the simple center element loading that
> Mosley used?.

End loading provides the most uniform current distribution. That 
causes the highest loop radiation resistance for a given element 
size, resulting in the lowest current for a given overall element 
length, phase, and and spacing. 

The loop radiation resistance progressively decreases and current 
levels in the loading system increase as loading is moved towards the 
feedpoint.    

Maximum loss reduction improvement is about a factor of four when end 
loading, properly implemented, replaces feedpoint loading. The catch 
is nothing else must change that hurts the system, like increased 
inductor losses. 

In other words if we have a base loaded vertical, or feedpoint loaded 
dipole, and we move the loading system from the feedpoint to the 
element end power loss can be reduced by a factor of four times 
is that is the only change made.  

When comparing a practical linear loading to lumped loading system, 
lumped loading is clearly superior for power loss and Q  IF the 
loading is properly designed. That's because lower loss effective 
resistances are possible with lumped components at HF.

> I've read that linear and center loading is better but can you really
> hear 1db? <:-)

It could be six dB, it depends on the quality of the designs! 

Don't write off lumped loading as "less efficient", most of that 
stems from folklore and improper or flawed analysis of 
various loading systems. 

Linear loading, despite claims it is "lossless", is anything but 
lossless. Most antennas I've owned and modified were  improved when 
"lossless linear loading" was replaced by what are often referred 
to a "lossy lumped inductors". 

Traps are always somewhat more lossy than an inductor because the 
shunt capacitance (used to resonate the trap) increases the 
circulating currents and loss in the trap.  Worse yet it does this at 
the expense of bandwidth.

There is almost no measurable difference between PROPERLY designed 
linear loading and properly designed lumped loading, and either one 
can be poor if improperly implemented.

73, Tom W8JI

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