[CQ-Contest] station re-building, distortion when multiple 600 Ohm lines in parallel?

[Joe]

I wonder if twisting one clockwise and the next closest one 
counterclockwise would aid in any coupling minimization?

They say open line is self shielding, but only to the extent described 
below. I remember growing up in the 60's when everyone had towers and 
big TV antennas and 90% were fed with 300 ohm "Twinlead"

I remember my Dad when he wanted signal to like a "Den" or Bedroom, he 
simply took some more twinlead and taped it for a foot or so parallel to 
the main feedline. No metal to metal contact, just tightly taped 
together, and hey it worked, the TV in the front room and other room 
would have just fine signals.

Joe WB9SBD
Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 3/16/2019 6:42 PM, Jack Brindle via CQ-Contest wrote:
> Most “600 ohm” open-line is not actually 600 ohms. I remember going through all the math of open line back in my Fields and Waves class in college. It needs spacing from other metallic objects in order to maintain its characteristics. I also remember learning directly from W1FB and W1ICP as to its benefits and how to handle it. I’m truly a believer in open-wire line (not so much for ladder line, although I use it). They affirmed that spacing is important in order not just to maintain characteristics, but to prevent signal loss and especially radiation. It needs to retain balance for that, something that my friend K9YC will tell you is hard to do, especially with antennas the way they are.
>
> I would space the lines as far apart as possible on those supports. Several feet should do. If possible route them differently, since they will couple if run in parallel for long lengths. Be sure to twist the open-wire along the way. Parallel lines have not just “connections” to each other, but to ground and anything else along the way as well. If you look at power lines (60 Hz), on long distance runs they are transposed every so often so that each of the lines has more or less equal ground exposure. Open-wire is only two wires, but the twist will have a similar effect, equalizing exposure to other elements in the vicinity. You also might take some hints from the telephone pole users and put T-arms on your supports so that you can separate the open-wire runs horizontally as well as vertically. This will allow you to place more runs on the existing poles.
>
> As K9YC likes to point out, everything is important; do your homework and make sure it is done right.
>
> 73!
> Jack, W6FB
>
>
>> On Mar 16, 2019, at 3:43 PM, K9MA <k9ma at sdellington.us> wrote:
>>
>> I think Holger means crosstalk, rather than distortion. The critical issue will be whether the feedline crosstalk is greater than that from the antennas. There may be ways to estimate the feedline crosstalk, but I don’t know without doing some research. However, it might be worthwhile spacing the wires for less than 600 Ohms as that will reduce crosstalk for a given distance between feedlines. The tradeoff will be slightly more loss due to more spacers.
>>
>> 73,
>> Scott K9MA
>>
>> ----------
>>
>> Scott Ellington
>>
>> --- via iPad
>>
>>> On Mar 16, 2019, at 11:48 AM, Jim Brown <k9yc at audiosystemsgroup.com> wrote:
>>>
>>>> On 3/15/2019 7:08 PM, Holger Hannemann wrote:
>>>> Does anyone has experience with potential distortion when operating parallel
>>>> running open feeder lines?
>>> Distortion requires a non-linear element in the signal path. Transmission lines are inherently linear. There IS the possibility of distortion in a ferrite core device used to transform impedance at either end of the line. Air core transformers would not have this problem.
>>>
>>> I think you're right to be concerned about crosstalk between multiple lines running parallel to each other for these long distances, which will be in addition to the crosstalk between antennas. In any event, you will need serious filtering for amplifier harmonics just as with any other multi-transmitter station.
>>>
>>> 73, Jim K9YC
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