Topband: shortened & low dipole for 160M--transmit/receive issues

[Tom Rauch]

> In order to improve the power handling ability of the traps---weight
> and size seem the limiting factors here, agree?  A coaxial wound
> trap/coil would probably weigh 8-10 lbs each using RG 211. Teflon
> might work, yes? Other L-C combos come to mind?  

I've been really slack at getting my Dayton talk on my web page, 
but I can convey several important results of a series of tests and 
measurements I did.

Coaxial traps are the worse commonly used trap. While losses are 
worse than normal L/C traps on the lower band  (160 in your case) 
they are still low enough to not be a factor. On the band where the 
trap is active loss can be 1 to 3dB depending on antenna and trap 
construction. 

By the way, some sources claim loss can be considered "loss per 
trap". That is not true. 

In an Inverted L, the trap actually has the same loss as a dipole 
with two traps of the same type! Power handling is 1/2 to 1/4 as 
much in an Inverted L trap using the same trap design as a dipole.

Higher loss in coaxial traps occurs because a "capacitor" made 
from coax has low Q, an inductor made from coax has low Q, and 
the L/C ratio is poor. coaxial traps not only have more loss, they 
also provide less bandwidth at the trap frequency.

I'd use L/C traps made from miniductor and transmitting-type 
capacitors. The 40 meter traps I copied from the ARRL Handbook 
had insignificant loss, and they could be scaled to 80 meters by 
doubling component values.  
 
> property.  My major concern on receive is that the North leg of the
> dipole will be parallel to a high voltage power line (about 50 feet
> away).  Would it be better for noise purposes, to slant that leg
> towards ground (in the manner of an inverted V),

Coupling in the nearfield is unpredictable, because the power line 
behavior is an total unknown. You will have to experiment, but the 
general rule is keeping distance and keeping them at right angles 
to each other.

Receiving is always the big problem on 160 for everyone.
73, Tom W8JI
W8JI@contesting.com