Did you put the diameter of the wire into Brian’s program?
304SS in the tables shows up as 2.5 IACS (i.e. 2.5 times the resistance of
copper). Because it’s resistive, the skin depth is greater (by sqrt(2.5)).
As long as you’re at a frequency that’s high enough where the skin depth is <<
diameter, then you can treat it as sort of a “rolled out flat” layer. So the
overall net increase in resistance is fairly small - the resistance is
2.5/sqrt(2.5) at high frequencies, getting more towards the DC ratio (2.5) the
lower you go.
In a coil, things are a big different because the skin depth isn’t nice and
uniform - it’s influenced by the field from adjacent turns, for instance.
For most dipole antennas, the resistive part of the antenna is small compared
to the 50-70 ohm radiation resistance, so the lossiness of the wire isn’t a big
deal. I believe the OP was looking at AWG 22? That’s about 16 ohms/1000 ft
(AWG 10 is 1 ohm/1000 ft, 10 gauges is *10 and 3 gauges is *2). On a 40 meter
long (120 foot ) dipole, that’s about 2 ohms, but the actual resistive loss
isn’t quite that, because the current’s not distributed evenly. But even so,
going from 2 ohms to, say, 4 ohms, out of 70 ohms is a small number (about 3%,
around 0.1 dB).
In a tank coil, with higher currents, and where the heat from the loss can’t
radiate to the surrounding air as easily, this might be noticeable. SS might
double the loss, and if it goes from 5% to 10% and you’ve got a kW of reactive
power (100W Tx, Q of 10), then sure - dissipating 10W is pretty noticeable.
On Sat, 30 Sep 2023 09:48:26 -0700, "jim.thom jim.thom@telus.net"
<jim.thom@telus.net> wrote:
From: "Lux, Jim"
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Antenna wire source?
If you're looking for strong and flexible, what about stainless steel
aircraft cable?? Sure, you'll lose a bit from increased resistance, but
maybe it's small enough to not matter.? 'DUY is looking at AWG22, so
it's already kind of lossy.
To be honest, I don't know if you can get SS flex cable that small - AWG
22 is 0.025" (1/40th) inch.? I've seen1/32nd. (0.03125") type 304.?
(hey, Grainger has 27/1000 diameter, that's pretty close - and they have
0.021, which is even smaller.)
SS 304 is about 2.5 times more resistive than Copper, but if we neglect
permeability (Is 304 non-magnetic?) the skin depth is twice what it is
in copper (at 10 MHz, 1.6 mil vs 0.8 mil), so the actual resistance is
about the same.
304 ss is normally non-magnetic (mu of 1.005 or something like that) -
but that might be an annealed piece.? Cold working (i.e. drawing into
wire) can change the crystalline structure and make it magnetic, and if
the mu goes up, then the skin depth gets thinner, so the resistance
would rise.? That's also measured at DC - the permeability could be
significantly different at HF.
## using K6STI's latest coil program, 316 SS is a full 7 times as much
resistance as copper,
on 160m. I have wound identical coils using silver plated copper,
copper, and also 304 SS. The aluminum coils ran hot. The SS coils ran
stupid hot.
## Then tried an experiment, replacing the 20m silver plated, tubing tank
coil in a hb linear, with an identical aluminum tubing coil. Both are
identical dimensions, spacing, form factor, and uh.
The aluminum tank coil ran way too hot.
## Dunno if any of the above pertains to wire ants. Myself, I would
just use RW-90 power cable, in whatever gauge you want. You can get RW-90
power cable in the outdoor version, that is water proof, and also UV
proof. I have used the regular indoor version....outdoors with wire ants,
and never had any issues. I bought 1000' of the 10 ga RW-90 years ago, at
a reasonable price back then. Stranded copper, easy to solder, or use
compression crimp lugs etc. Dunno how small a ga you can get RW-90 in.
Jim VE7RF
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