[TenTec] open wire feed line

[Sinisa Hristov]

NJ0IP wrote:

> Paul, just a word of caution when sourcing the stuff.


One more word of caution:  most plastic ladder lines
use copper clad steel conductors. Such lines are only
suitable for low SWR applications, and in this respect
they behave more like RG8 coax than like true open wire lines.

Copper clad lines will introduce several dB's of loss
in a typical "multi band doublet" applications.
Depending on circumstances, this may or may not be acceptable.
To me, it was acceptable until few weeks ago, but not anymore :-)

Also, "multi band doublet" applications need significantly
higher characteristic impedance than found in plastic lines.

Here is some measured data on "450 ohm ladder line,
#14 gauge, stranded wire" bought at Radioworld,
Toronto, ON, http://www.radioworld.ca :

k = 0.91

Characteristic impedance  Zo = 335 Ohms
(considering wire gauge and distance,
 Zo cannot be over 360 Ohms even without plastics,
 i.e, the distance is too small)

DC resistance = 91 mOhm/m  (7.5 times that of copper!)

matched loss at 14 MHz:  0.71 dB/100 ft

this translates to 2.65 dB/100 ft with SWR = 10,
and to 4.25 dB/100 ft with SWR = 20;
SWR = 20 is easily achieved with multi band doublets
because the Zo is too low

matched loss at 42 MHz:  2.12 dB/100 ft


73,

Sinisa  YT1NT, VE3EA