The AM Forum

I have option of running my OWF out to about 500 feet from the shack. Wondering about what type of open wire feedline to use. I have about 2500 feet of .1875" (3/16") stranded stainless cable that I have had for years. My thinking is if I would use this, I would be able to pull it tight between some 4 x 4 posts spaced every 50 feet. No flopping in the wind and no spacers needed. This would be about 8 feet off the ground and above the farm animals.

I know SS rates on the bottom of the list as far as conductivity!

What's your thoughts on using SS wire for this purpose?

Regards,
Larry

I think you have the makings of an excellent antenna system .... just think of the ss cable as a rugged support for some copper wire feeders ... to avoid electrolysis effects use something like 14 ga THHN wound around the ss cable say 1 turn per foot and fastened with uv proof tyraps ...bet it works great

Stainless Steel wire would be a poor choice for transmission line with high losses.  Sorry.

I agree,  sell the stainless cable to someone who can use it and buy copper wire to make your feedline.

Sorry, have to disagree with this idea.

Hi Larry,

I agree with the gang. I will pile on.

I have actually tried stainless steel aircraft style cable for both a dipole flat top and OWL feeders. I was not happy with the results.  If there is a high swr on the feed line, then the hot spots can get ridiculous, since the conductivity of SS is so much lower than copper. Even copper will be lossy if thin wire is used and the swr is super high on certain bands.

That's a good idea about using no spacers -and poles every 50' for the OWL. I did it with 2' spaced OWL pulled tight off the tower, no spacers. Wonderful environmental stability. In the wind there may be a small variation in swr, but the wider, the less effect.  

T

Tom,  got this backwards??

Yeah, I did, Fred. You media fact checkers...  ;D

SS is about 40 times less conductive than copper.   I suppose if we had a large cross sectional area compared to copper, things could be made equivalent. Skin effect would help the SS too.

Here's a few notes off the web:

Stainless steel is a really poor conductor compared to most metals. This source lists it as 7.496�~10 −7 ƒ¶⋅m
7.496�~10−7ƒ¶⋅m which is more than 40 times worse than copper.

The reason is that conductivity in metals is high is that metals form a crystal lattice where the outer shell electrons are shared and easily move through the lattice. When the lattice has imperfections the flow of electrons is retarded. Stainless steel is an alloy of iron with up to about 25% chromium (and sometimes a small amount of nickel or carbon) added for corrosion resistance. The chromium atoms disrupt the regular iron lattice and increase the chances of inelastic collisions with moving electrons.

What about the "copperweld" type line? Is it but a thin coat of copper over steel?

Skin effect,  signal only runs along the surface of the conductor.  Higher the frequency the shallower the signal travels along the conductor.

It sure will make an antenna broadbanded.   I giggle every time I see someone singing praises on a "horse fence antenna"....   Stainless steel wires wooden through 2 inch webbing.

Broadbanded as a dummy load!

--Shane
KD6VXI

I don't think you paid carefull attention to what I was saying .... if you do as I suggested you would form a superior 'copperweld' type of conductor with better temperature stability than just copper ...less sag in the hortizontal run than plain copper

Thank for the reinsurance that the SS wire is in fact not much use for RF. I guess there was a reason it's bin sitting under shelf for 15 years!

What do you think the minimum gauge wire would be if the supports were about 50' apart and trying to use the least amount of spacers? I would  guess 10 gauge may work?
Thanks all---- now I better get back to work!   hihi

Larry
 

That stainless cable would make a pretty good dissipative line.  A few years ago I was working on some HF antennas at one of our domestic Air Force bases.  They had a wonderful old stacked rhombic array on site that was scheduled for removal and I took some time to inspect it.  The radiators were heavy phosphor bronze wire.  At the far end, where the terminating resistor is shown on most diagrams, there was an open wire feeder heading toward the bottom of the end support tower.  This line was made of nichrome wire.  When the open wire neared the ground, it was turned to horizontal and went back and forth on supports a few times to use up extra length.  Finally, it terminated in a bank of non-inductive resistors, which provided the termination that made the array unidirectional.
By virtue of the chromium, stainless and nichrome have much in common. Using the available stainless wire as feedline is tempting, but it would make for a very lossy antenna system, although it would appear to be broadband.  We work too hard for our watts to throw them away as heat.  That stainless cable might make a good guy wire if it's fat enough.

I have several antennas made from stainless welding wire that have been  up for  years.  BUT!, they are fed with regular OWL. that is copperweld.  The method of
joining the feed line to the stainless is the tricky part.  I use the small split nut type connectors and coat them with liquid tape or some other good water proofing
compound.

running copper around the SS core will create an inductor - how much inductance would depend on if the wire was insulated or not (uninsulated would be shunted by the R of the SS every turn, so lower Q).

Maybe someone could get a wire rope company to run some wire rope with one or more strands being copper (the strands in wire rope
generally being thinner still wire made into small ropes then they are made into the thicker rope)? Bronze has been used in stranded form, woven for antennas too... also some wire rope has a non metal core, one could substitute copper there - no clue how copper surrounded by SS would fare.

Who wants in on a group buy?

              _-_-bear

one thing to remember is that he has the ss cable on hand

ok ....I got more curious about skin effect and its effect on ac resistance...

from 4th ed Ref Data for Radio Engineers (pub ITT) on page 131 there is a formula to calculate ac resistance for a conductor compared to copper .... I don't have the ability to express it here with just an ASCII keyboard .... I will try to cut to the chase .... assuming 40 times greater dc resistance for stainless steel than copper when the square root of that is taken yields 6.3 times .... this means that for the stainless steel conductor diameter must be 6.3 times the copper conductor diameter to yield the same ac resistance ....so here goes

.1875 / 6.3 = .03 inch   which is the diameter of a 20 ga copper wire .... so if a 14 guage copper wire
( dia .0641) is paralled with the .1875 inch stainless steel (messinger) wire then the majority of the rf current will flow in the copper wire and a lesser amount in the ss cable

how is this so ? ....it seems than the lower conductivity conductor has a greater skin effect depth than does the copper one

Real world experience....I have a 900 ft pc of 7 x 19 SS 1/8 inch diameter cable  over 100 ft above ground.....It has NEVER worked  good as a long wire antenna altho it would tune to  almost any freq...It is now going to be used as the boom for a wire beam...
  I like Beefus Idea about the spiral wrap of THHN over the SS cable...I'd be interested to hear how that works if you try it...Good Luck..

It work atrociously.  The "spiral wire" = solenoid wound inductor!!!

if my intention had been to stir things up, I guess it worked  ;D

Cactus K4YMB has noted that he will try this in a construction .... first as ss cable dipole, then as copper wire dipole, then as a hybrid of both ....plans are for 40 mtr inv vee at 30 ft at the center with current balun ....field measurements to be made 500 ft away...

we shall see ... 

I doubt he will see much difference in that test. There is only one MATCHED ~70 ohm current peak at the center and the rest of the dipole impedance increases dramatically to the ends. Losses will be minimal.

The original question asked about using a long open wire feed line and flat top - both made of SS wire with huge mismatches - and had the potential to operate on the higher bands, 10-20M where there will be many very low (10 ohm) high current hot spots as well as higher skin effect.  Run a test like this and you are more likely to see the effects of high current losses on SS.

T

yes yes yes ....an excellent observation .... this has made a few things add up .... many folks have used various steels for low band antennas with good results which on the first hand appears to dispute the veracity of of the ac resistance calculations ... the comparison of feed impedance to radiation resistance speaks to efficiency .... in addition the calculation of permeability is heavily dependent of the steel alloy .... this has turned into a knotty problem to resolve accurately .... if Cactus is still interested, we may try what you suggest ....thanks to all for their inputs

Here's a photo from a visit to the Greenville VOA site - IIRC, this is stainless line used as the 250KW terminating resistor for a rhombic. The line runs back and forth until shorted as shown in the upper left.
http://www.virhistory.com/ham/voa/P1010102.JPG

Cheers,
Nick K4NYW