[Antennas] Balanced line optimum conductor spacing?

2002年1月06日 07:03:44 -0800

At 03:54 PM 1/5/2002 -0800, you wrote:
>Again, what would be useful would be a rule of thumb along the lines of
>"conductor spacing should be between something like 0.1% of wavelength and
>0.5% of wavelength". This is going to be somewhat subjective in terms of how
>much radiation we can tolerate vs how much loss we can tolerate, but it
>seems to me we should be able to come up with some sort of useful
>guidelines.

Interesting question! I went digging through my library to see what I could 
find on this subject. Oddly enough not too much. In John Heys, G3BDQ, book 
"Practical Wire Antennas" he states "... spacing can be remarkably wide 
before they begin to radiate, and spacings of 6in (15cm) are in order, even 
on the 28 MHz band. This means that on 1.8MHz the feeder could have its 
wires 8ft (2.4m) apart before any significant feed radiation took place!"
He doesn't give any references for the above, but using he statement it 
would appear that he suggest a maximum distance is on the order of 
0.015-wavelength.
Another possible source I noted was in the ARRL antenna book's graphic on 
feed line losses. On this graph 450-Ohm window line ends at 150 MHz. As 
this line's spacing is 0.8 inches would indicate that the maximum spacing 
to be 0.01-wavelengths.
So at this point it seems that something around 0.01-wavelength may be good 
choice for maximum spacing. Does anyone have a additional information or 
thoughts on this?
As far as how close the conductors may be spaced I would think the 
consideration would be the point were voltage breakdown would take place. 
So that would be dependent more on the power applied and what dielectric 
was being used. Additionally, lower impedance lines have higher losses as 
they are carrying higher currents for any given power level that the higher 
impedance lines. However for tuned lines all bets would be off.
Comments, ideas or suggestions?
73
Danny, K6MHE