Topband: Low Loops, Tee's and ...

[Tom W8JI]

> Why do not more folks use the Half-Square antenna ? With its Hi-Z feed 
> point it makes a great candidate for areas with poor soil conditions. It's 
> performance here at CN98pi
> on 160-meters in a glacial outwash deposited silt/sand/gravel river valley 
> seems to be as good as I could hope or expect. This antenna either works 
> very well OR you guys along the East Coast have superb 'ears' to hear my 
> 100-watts during the contests.
>

The reason it appears to have a higher feed impedance is the half square is 
like half of a folded dipole, really fat, with only one conductor is fed. 
The antenna has the same net current into earth, it is just split between 
two points instead of one. This cuts the current into any ground system in 
half for a given power.

While we might initially assume this is 1/4 the power loss, it isn't. Let's 
say each ground is 25 ohms and look at it.

With 4 amps, ground loss would be 400 watts.

If we split that current to two 25 ohm grounds, we now have 2 amps or 100 
watts loss per ground. That's a total loss of 200 watts by having half the 
current into two poor grounds.

If we simply took that second ground and made one ground system twice as 
good, we would now have 4 amps into 12.5 ohms or 200 watts loss.

So we see, putting the second ground system work into the feedpoint and 
reducing resistance to half is the same loss change as the current split 
into two grounds with a half-square antenna, each one cutting ground loss in 
half for a given radiated power level.

RCA had a multiple drop system on VLF up in the northeast. They found they 
could more easily work on a single ground. When they did that, they could 
push a single ground down in loss to work better than a distributed ground. 
As I recall, their multipoint ground was actually several ground points, not 
just two, and they made it better by doing one good ground!

On the other hand, a good ground can be work in some locations. A half 
square might be easier for the same change.

This darned free lunch is always disappointing.

There are a dozen ways to implement things, and they all have pros and cons. 
It's really difficult to see a 3-5 dB level change without a good A-B test, 
so it really boils down to what makes us happy. If we are happy, it is like 
magic. It is as good as an extra 10 dB. This is true no matter how our 
antennas actually work.    :)

73 Tom