Will steel wire work as well as copper for antennas?

[eeemcee]

Seems to me in that an antenna is carrying microamps at most that slightly higher resistance of steel Vs copper wouldn't matter.
What's the fault of this logic??

 

[berkeman]

Seems to me in that an antenna is carrying microamps at most that slightly higher resistance of steel Vs copper wouldn't matter.
What's the fault of this logic??

Sounds reasonable to me. We often use aluminum or steel for antennas anyway. I don't know that I've seen any copper antennas, but they probably exist.

EDIT -- we do use some "wire" antennas, and they will typically be stranded copper. But we are using copper in those cases just because that is how insulated wire usually comes...

 

[yungman]

Yes. Current is so low it really doesn't matter.

 

[berkeman]

Thread locked for Moderation...

Thread re-opened after deleting a number of nonsense posts and our responses.

 

[rbj]

Thread locked for Moderation...

Thread re-opened after deleting a number of nonsense posts and our responses.

i would have liked to have seen those.

i remember when i was a ham radio person that there was this product called "copperweld" that was copper on the outside and steel on the inside. it was supposed to be stronger for long wire or dipole antennae. i remember it was shipped in a big coil and it sort of had a mind of it's own.

maybe it was a marketing trick/

but the difference in resistance is pretty small.

 

[berkeman]

i would have liked to have seen those.

 

[dlgoff]

Back in the day, my mentor Ham friend, W0AFQ, explained how, on field events, they would load up barbed wire fences.

 

[eeemcee]

I recall seeing radio stations' ground planes being copper wire

As a ham in the 50's it was the standard form to use the copper coated steel wire if not just copper and aluminum was considered a lessor approach, I had a 800' longwire of aluminum and it stretched.

 

[Averagesupernova]

I think the reason that the cooper coated steel is used is to prevent stretching. Copper alone will stretch as well as aluminum. I know a ham who had a tri band yagi that had a coil open up in one of the traps due to arcing or possibly lightning. The fix was to stretch the heck out of it so it was long enough again. Obviously the point it had burned off was not in the middle of the winding or something. Only a few turns in so he could make up for it by stretching.

 

[the_emi_guy]

You may have to be careful here depending on your operating frequency, lengths involved, acceptable losses, and the details of the steel wire such as its surface treatment.

At RF frequencies, the high permeabililty of ferrous metals makes them lossy (small skin depth). Consider:
1 meter long AWG14 wire at 100MHz:
Mild steel (resistivity 0.2u-ohm-m, and ur = 800) yields 49 ohms resistance.
Copper (resistivity .0169u-ohm-m, and ur = 1) yields 0.5 ohms resistance.

Also, steel is not all the same. Stainless steel has ur = 1. Galvanized steel wire will have a layer of zinc which may be thick enough to carry your RF current, or maybe not, you would have to know the plating thickness and do the math.

For an antenna, you want the conductor resistance to be sufficiently below the radiation resistance of the antenna. For example a halfwave dipole antenna with radiation resistance of 73 ohms, 10 ohms of conductor resistance causes 1dB of loss. This may be ok in some applications, but if it is a high power transmitter you can have a lot of heat coming off of the wires, and since it is a skin depth issue, just going to a bigger wire may not be the answer.

If the radiation resistance is very low the problem is worse. For example electrically small loop antenna made resonant with lumped components at the feedpoint are sometimes built out of 1/2 inch copper plumbing pipe and still have low radiation efficiency due to copper losses.

As mentioned by previous poster, copper clad steel (CCS) wire is popular for antennas, skin effect confines RF current to copper. CCS cable is used for CATV cable for the following reasons:
1 - Copper cladding is thick enough that skin effect limits current to Cu minimizing loss.
2 - Copper cladding is thin enough that it is too expensive to reclaim the Cu from scrap. This makes the cable not a target for theft.
3 - The steel center conductor is strong enough to serve directly as the male connector center conductor.

 

[davenn]

Thanks the_emi_guy,

you have confirmed what I was going to post here and what I had known for a long time
Although, iron or steel wire will work, it is lossy because of the extra resistance when skin effect is taken into account ... and as one old saying goes you waste too much RF energy just heating the wire instead of radiating it ;)

regards
Dave

 

[berkeman]

Yeah, I've learned some useful things in this thread as well. I've never seen the copper-coated antennas that have been mentioned (and I've worked with a *lot* of antennas) -- I need to do some more reading about this...

 

[rbj]

I think the reason that the cooper coated steel is used is to prevent stretching. Copper alone will stretch as well as aluminum.

why not just make it pure steel?

 

[davenn]

why not just make it pure steel?

cuz it rusts and breaks, it still has the resistance problems, its not flexible, it cannot be soldered to easily, all of those making it harder to work with

in my days long ago working for Telecom New Zealand, they has this wonderful idea to use plastic insulated copper clad steel it was a twin wire ie ... figure "8" mainly used to bring the phone line into the house/building from the pole on the street.
Unfortunately, it was often run over much longer distances ... some times many km's across farmland etc where shotgun pellets from farmers, doing pest riddance, would nick the plastic and copper cladding ... some time later, months or several years the steel would rust through and somewhere out in the middle of a span there would be an open circuit developed.
It would leave us field techs mumbling and muttering about the stupidity of copper clad steel.

Ohhh ... for open wire phone lines, hard drawn copper was normally used, because it didnt stretch like softer/purer copper.

Dave

 

[eeemcee]

VERRY interesting! I'm interested in a longwire for general and ELF reception, not having several states to run it over like Wisconsin it will not be long enough but receivers aren't too touchy, at 30 Mhz, it will function as an end fire antenna with lobes off the ends, I guess. Still, it will probably do the job of scooping the microvolts up and delivering them to the receiver.
The FCC in it's benevolence has just allowed hams to operate on, I recall 150 Hz with (oh WOW) one watt or thereabouts. Here, the concerns about radiation resistance etc. WILL be a concern--CQ DX--how many feet?
cheers