I think I agree wholeheartedly with John, W6NBC about the "fear" of using open-wire line near ground or even close to metal.
I ran across his testing well after I did some of my own (with twinlead, some old RS 300 ohm stuff, and a leftover chunk of 450 ohm window line). I was playing with zipcord as a feedline, and yes of course it DID have the inherent loss that has been recorded for years, but I was amazed that it didn't seem to be so touchy - even running around indoors on the floor!
I ran across his testing here:
http://w6nbc.com/articles/openwireline.pdf
I think I had seen this before and doubted it - largely because my own efforts at using open-wire were stymied by not having my own common-mode on the open-wire choked! Once I got common-mode under control, the open wire became usable - even laying very close to soil and concrete even.
The keyword to making this work is to cure your common-mode current in any way you can. For the longest time I thought that "balanced line" to a "balanced antenna" was a magical cure-all for common-mode. Not so - maybe because I could visualize how common mode works on coax, I couldn't visualize that a balanced 2-wire conductor can carry that common-mode current as well.
This could open up a wider world of possibilities for some antenna projects. Just take care of common-mode issues first and I think you'll find open-wire "tame" if not taken to absurdity / unsafe levels. I'm not going to run 1KW on twinlead on the carpet.
I ran across his testing well after I did some of my own (with twinlead, some old RS 300 ohm stuff, and a leftover chunk of 450 ohm window line). I was playing with zipcord as a feedline, and yes of course it DID have the inherent loss that has been recorded for years, but I was amazed that it didn't seem to be so touchy - even running around indoors on the floor!
I ran across his testing here:
http://w6nbc.com/articles/openwireline.pdf
I think I had seen this before and doubted it - largely because my own efforts at using open-wire were stymied by not having my own common-mode on the open-wire choked! Once I got common-mode under control, the open wire became usable - even laying very close to soil and concrete even.
The keyword to making this work is to cure your common-mode current in any way you can. For the longest time I thought that "balanced line" to a "balanced antenna" was a magical cure-all for common-mode. Not so - maybe because I could visualize how common mode works on coax, I couldn't visualize that a balanced 2-wire conductor can carry that common-mode current as well.
This could open up a wider world of possibilities for some antenna projects. Just take care of common-mode issues first and I think you'll find open-wire "tame" if not taken to absurdity / unsafe levels. I'm not going to run 1KW on twinlead on the carpet.