[TowerTalk] Wire Size for 800 meter longwire

[K4SAV]

An update on the 800 meter long wire performance.

Using 17 ga aluminum wire vs 0.5 inch galvanized cable I had first 
assumed, decreases the gain by about 3.7 dB.

The antenna pattern is very sensitive to the exact overall length. 
Looking at it another way, it is sensitive to frequency change.  A 
frequency change of 50 KHz changes what used to be a peak lobe into a 
null (looking mostly at the pattern off the end of the wire).  For 
example, off the end of the wire, at 1.8 Mhz and an elevation angle of 
10 degrees the gain may be -1 dB.  Move to 1.85 MHz and the gain is -13 
dB, same angle.

The method of feeding the wire also effects the pattern.  I assumed end 
fed with the shield dropping straight down into the salt water.  This 
seems to produce the best pattern I could find.

Implementing a vee beam with an 80 degree included angle seems to reduce 
the pattern into something that is very scrambled and with lower gain.

I am normally unsure about simulator performance when wires are close to 
the ground, but in this case since this is an almost perfect ground, 
this seems to be within the guideline of the simulator.  The simulator 
shows very little difference between using perfect ground and salt water 
except between 0 and 3 degrees elevation.

Jerry, K4SAV

>
>  
>