Topband: Need antenna advice

[GEORGE WALLNER]

On Thu, 11 Feb 2010 20:07:29 -0800 (PST)
  Mike Waters W0BTU <mrscience65704 at yahoo.com> wrote:
> why my transmitted signal on 160 might 
>be so weak.
> I can only run 100 watts at this time.
> 
> I tried the inverted-U antenna as described in the links 
>below. It is very similar to the one that K3LR used in 
>the first link. The antenna is over the top of a 60' oak 
>tree, and the two elevated radials are about 10' high.

  
Mike,

Think of all the compromises you have made: 100 watts, 
only two semi-elevated radials, antenna wire wrapped over 
a tree, inverted U, perhaps more...

Without details it is not possible to pin-point the exact 
cause of the poor performance, but most likely it is due 
to all of the above compromises adding up. Yes, you can do 
well with 100 watts, but you need an efficient antenna. 
And, yes, the inverted U with only two radials will work, 
but you may need more power, and so on… On TB there is no 
way to do dodge the need for a good antenna or more power 
–or both. The most important part of the antenna is the 
radials, the more the better. Unless the antenna stands 
over salt-water, you will need a lot of radials. The 
ground is a big resistor (in both senses of the word) and 
it is in series with the antenna return currents. 
According to Ohm’s law, the antenna currents will be less 
and whatever power goes into the antenna will be mostly 
dissipated in the ground. It has more resistance than the 
radiation resistance of the U and there will be a 
correspondingly larger voltage drop on it. P = I x U. That 
is probably where 80 of your 100 watts go!

George, AA7JV