[TenTec] open wire feed line

[Denton]

Does this mean that one should homebrew or purchase true ladderline. If this 
is the case, would 450 ohm or 600 ohm ladderline be more  appropriate for 
multiband doublets?
----- Original Message ----- 
From: "Sinisa Hristov" <shristov at ptt.yu>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Friday, September 30, 2005 2:50 PM
Subject: Re: [TenTec] open wire feed line


> 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
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