Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Best wire for long wire antenna
Owen Duffy wrote:
. . . I do remember Roy discussing the resistivity of rust, but I don't recall figures... does anyone have any figures for the resistivity of the rust coating on a rusted steel wire? I guess its permeability is also relevant to RF resistance. No, I don't believe I've mentioned rust, although I've commented on copper and silver salts a couple of times. I wouldn't try to guess what the resistivity of rust might be, since it would surely vary a great deal with the amount of hydration. A highly resistive coating won't add appreciable loss, nor will a highly conductive one. There's an in-between range which will. But keep in mind that the skin depth is inversely proportional to the square root of the conductivity, so a thick coating with twice the DC resistivity will increase the RF resistivity only by a factor of about 1.4. The real problem with thinly plated steel wire is that if and when the coating corrodes off -- or if it's too thin to begin with -- the current ends up flowing in the steel itself. Steel is terribly lossy stuff at RF chiefly because of its permeability, not that its conductivity is all that hot to begin with. Skin depth is inversely proportional to the square root of permeability, so a steel with permeability of 100 has 1/10 the skin depth it otherwise would, resulting in 10 times the RF resistance. If you consider half wavelength antennas at various frequencies all made from the same size wire, you find that the loss gets worse as frequency decreases. So it's often more of a problem on the lower frequency bands. Some stainless steels are magnetic and some aren't. Magnetic ones are much lossier at RF for the same reason as ordinary steel. Roy Lewallen, W7EL |
#2
|
|||
|
|||
Best wire for long wire antenna
The 'best' wire for long antennas is whatever you happen to have
the most of that will support it's own weight. After that, it's more a matter of what color insulation you think is nice. And after that, it's whatever you can convince yourself that you can afford. Have several pieces of different wire size/type? If they will support their weight, splice the @#$ things! Paint it all pink. Pink works very well for antennas. - 'Doc |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Transformer Wire = Magnet Wire as a a Light-Weight Antenna Wire {Hidden] Stealth Antenna | Shortwave | |||
ABOUT - Wire Antenna Life - How Long should a Wire Antenna Last ? | Shortwave | |||
long wire antenna | Antenna | |||
Long wire antenna | Shortwave | |||
Long wire antenna | Antenna |