Thanks Frank for running the program and for the results. They give me a
good confirmation of what Riachard Clark showed me, I need to get more space
between these feeds than I was planning on. If I had 3 feeds, I guess I
ought to have a cross arm on my wood/PVC poles coming in and spread the
feeds by about two feet to minimize the interaction down to a miniscule
amount. I really do want to feed the antennas separately. Gee, I wonder
what W6AM used to do with his 10 or 12 rhombics fed with open wire all
coming into his home...

73,

Greg, N6GK


"Frank" wrote in message
news:xqNHe.177484$tt5.93925@edtnps90...
"greg knapp 5" wrote in message
...
I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to
run the feeline from each about 200 feet from the back pasture to the
shack. I don't want to walk out 200 feet and throw knife switches to
chose the antenna/feedline I want to feed, so I plan to run separate 600
ohm open feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably
150-200 feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough
separation? What other precautions do I need? Need they be twisted if
they are not near anything other than the other feed lines?
Any help is appreciated.
73,
Greg, N6GK

Hi Greg:

I have just run a free space NEC 2 model of a pair of horizontally
positioned 6" wide, 600 ohm, transmission lines, vertically separated by
12". The model was run from 29 to 31 MHz. On 30 MHz , with both lines
terminated in 600 ohms the isolation was about 39 dB. With both lines
terminated in 6,000 ohms the isolation improved to 66 dB. The actual
range of impedances will be much higher, and complex, but it does give an
idea of the order of magnitude of the isolation. The calculation is based
on the ratio of the peak currents observed.

Hope this helps,

73,

Frank (VE6CB)