Stainless Steel Wire - OK for antennas?
 

I recently acquired a large quantity of very flexible stranded
stainless steel wire at a garage sale. It is about 0.85 mm (around
1/32 inch) in diameter and extremely strong. I was wondering if this
could be used for wire antennas for HF. I seem to remember seeing
something about SS not being ideal. Is this a real consideration or
just a matter of being too finiky?

Thanks - Dave

On Mon, 23 Aug 2004 18:11:53 -0400, Dave wrote:
just a matter of being too finiky?

Hi Dave,

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

73's
Richard Clark, KB7QHC

I recently acquired a large quantity of very flexible stranded
stainless steel wire at a garage sale. It is about 0.85 mm (around
1/32 inch) in diameter and extremely strong. I was wondering if this
could be used for wire antennas for HF. I seem to remember seeing
something about SS not being ideal. Is this a real consideration or
just a matter of being too finiky?

Thanks - Dave


The best use of it would be for the Beverage receiving antennas. Extra
resistance helps to retard the reflected wave and "sharpens" the pattern.

Otherwise it would beat the heck out of DLM, EH, CFA or Fractuled antennas.

Yuri, K3BU

I recently acquired a large quantity of very flexible stranded
stainless steel wire at a garage sale.
was wondering if this
could be used for wire antennas for HF.

Of course it could be used. The resistance loss is insignificant. It will
actually increase your SWR bandwidth. Certain Comercial Ham antennas use a
fixed resistor to improve bandwidth and lower SWR. So go for it and see what
happens.


73 Gary N4AST

It will be strong but the trade-off is the higher resistance/loss.

Oly thing I don't like about the stuff is that it can cut you, if too small.
Copper just breaks.

The best thing about it is - you already have it. Use it.

"Dave" wrote in message
...
I recently acquired a large quantity of very flexible stranded
stainless steel wire at a garage sale. It is about 0.85 mm (around
1/32 inch) in diameter and extremely strong. I was wondering if this
could be used for wire antennas for HF. I seem to remember seeing
something about SS not being ideal. Is this a real consideration or
just a matter of being too finiky?

Thanks - Dave


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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

On Tue, 24 Aug 2004 09:56:29 +0300, Paul Keinanen
wrote:

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.

Hi Paul,

And still, no one would notice. In fact, I gave the loss 100 Xs
copper, lowered the frequency to 1MHz and saw roughly 6dB loss - the
"standard" S-Unit, against which propagation variations would toss
that around to wider variation. I suppose it wouldn't do for EME, but
I don't know any work at 1MHz for EME.

Still, and all, this determination is easily within the scope of the
free distribution of EZNEC which allows any user to make an informed
decision about a choice being OK.

73's
Richard Clark, KB7QHC

On Tue, 24 Aug 2004 09:56:29 +0300, Paul Keinanen
wrote:

Two corrections:

An other source specified the stainless steel resistivity as 43E-8
ohm/m

The unit of resistivity is of course ohm m (not ohm/m).

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:-).

With 50 % efficiency (-3 dBd gain), the losses are about 800 W and
when divided evenly along 80 m will give 10 W/m (not 1 W/m), which in
addition to frost will also melt ice and keep the birds away :-).

Paul OH3LWR