[Elecraft] OT: Feedline Question

[Guy Olinger K2AV]

Hi, Jim,

What you appear to refer to by "open wire line" is BARE wire with small
spacers widely separated. Performance changes a lot if the "open wire line"
is constructed with unstripped THHN. Particularly with surface tension on
new THHN. Where hung on the level in a misting rain, I have seen a droplet
per centimeter hanging on THHN insulation. Along with a rather large
variation in Z as seen in the shack.

Just one more reason to keep to bare wire. Bare wire sloughs rain.

I remember 300 ohm TV open wire line from bare #18 copperweld with molded
spacers every three inches.

The 300 ohm ladder line if run near a furnace or fireplace flue would "go
bad" on TV channel 2 as well as the UHF channels. There was also this
phenomenon called acid rain which could severely modify electrical
behavior, including etching the copper conductors.

With the PE formed 300 ohm line, the reduction in signal strength could be
blamed on "the rain", which was true in one sense. But since it got better
when it dried up, the PE supported balanced line would never get the blame.

73, Guy K2AV



On Tue, Apr 18, 2017 at 1:37 PM, Jim Brown <jim at audiosystemsgroup.com>
wrote:

> On Tue,4/18/2017 10:10 AM, Guy Olinger K2AV wrote:
>
>> Then there is the loss based on number of spacers and loss tangent of the
>> spacer material modifying the lesser air loss.
>>
>
> Below UHF, loss in transmission line is virtually all due to copper losses
> unless the dielectric material is wet or is otherwise made conductive.
>
> Quite a few years ago, N6WS did some excellent work showing that losses in
> window line are greatly increased when it is wet. His work was published in
> QST and later included in Antenna Compendium #6. It should be required
> reading for anyone considering window line. He measured four types of
> window line and some open wire line he built himself. Putting some numbers
> to it, Wes's measurements showed loss at 50 MHz increased from about 0.4
> dB/100 ft to more almost 6 dB/100 ft when it was wet. The open wire line
> showed no increased loss when wet.
>
> 73, Jim K9YC
>
>
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