On Mon, 23 Aug 2004 22:26:34 GMT, Richard Clark
wrote:

Yes. No one is going to notice something less than half a dB (which
by definition is unnoticeable).

This may be true for upper HF, but for MF/low-HF dipoles the situation
may be a bit different. The dipole length is inversely proportional to
frequency and the skin depth (and hence AC resistivity) is directly
proportional to the square root of frequency. Thus the net effect is
that the total dipole resistance is inversely proportional to the
square root of the frequency. Thus a dipole cut for the lower band has
a larger resistance than an antenna cut for a higher bands, provided
that the same wire type is used.

The resistivity and skin depth depends on the material and apparently
varies quite a lot depending of the type of stainless steel, since
various sources give quite different values.

The skin depth for copper at 1.8 MHz is about 50 um, while for some
stainless steel, it appears to be around 200 um. Both values are well
below the OP's 850 um conductor diameter.

One source claimed that the stainless steel has a 52 times DC
resistivity compared to copper, so factoring in the large skin depth,
the AC resistivity at 1.8 MHz would be more than 12 times that of the
copper wire of the same size.

An other source specified the stainless steel resistivity as 43E-8
ohm/m and while the 0.85 um diameter conductor with 0.2 mm skin depth
would have an effective cross section of 0.4 mm2 and with the 80 m
length of the 1.8 MHz dipole, the total resistance would be 86 ohms.

Compare this to the nominal 73 ohm radiation resistances for a half
wave dipole and more than half of the transmitter power would be
dissipated in the losses.

However, since the current distribution is not uniform along the
dipole, the effective losses are not that quite as bad. On the other
hand, if the dipole is close to the ground, the radiation resistance
is well below 73 ohms, so again, we are in the -3 dB efficiency
ballpark value.

With a 1500 W transmitter, the losses are about 1 W/m, this should
help melting any frost accumulated on the wire during a cold night:-).

Now the question is, is this 80 m stainless steel strong enough to
support itself, even if supported in the middle at the feed point.

For a copper wire with the same diameter, the resistance would have
been below 10 ohms and the losses about 0.5 dB.

Paul OH3LWR