Source for stainless steel tubing (small diameter)

I am wanting to get into amateur radio antenna building most plans for a j pole antenna I have seen use 1/2 inch coper tubing. I was wondering
if I could use stainless steel to make it rust proof. Any ideas where one could cheaply get small diameter stainless stell tubing? Any of you out there work with amateure radio antennas?
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Stainless is readily available, it's non rusting, and is also much siffer than copper so you can use thinner wall. Downside is that it ahs much higher resitance than copper, tends to mess up both the gain from the antenna as well as the exact dimensions.
snipped-for-privacy@hotmail.com wrote:

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Stainless would work OK for a j pole. You probably couldnt notice the difference by ear when operating at frequencies below 400 MHz. It has always been my experience with HAM antennas that I wouldnt invest much time in any design that wasnt close to *the best* performance. Copper is really a good performer for antennas. Aluminum, is often a necessary compromise. Stainless is great for automotive mounted antennas. I suggest you post your question on Rec RadioAmatuer Antenna. There are some *very* well informed guys there.
Jerry
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Jerry Martes wrote:

for
wondering
where
the
invest
Copper
necessary
There are

Would making the stainless steel j pole elements slightly larger in diamter compared with a copper j pole plan over come the higher resistance?
I thou8ght about aluminum but dont have the capability to weld it. I thought with stainless I could fishmouth the tubes and weld them together. I am just thinking at this point.
What about using EMT tubing? Is this rust resistant? It is cheap and light and easy to work with.
I love fooling around in my garage with stuff. I was wondering if it was possible maybe to make a few bucks doing this as a hobby. I have a seocond child due any day and money will soon start to be hard to come by!
Think this is a possibility? ANything else out there a guy could do in his garage in his spare time to make a buck?
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Why not just use copper pipe? It won't rust. You could weld them up if you don't want to use pipe fittings.
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Copper is kind of ugly and tarnishes which I would think would increase the resistance over time.
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This is your project and you can use any material you want. But you have no reason to *not* use copper because of the degradation of the electrical characteristics when it gets tarnished. The RF resistance of the tarnished looking copper wont be degraded. I havent seen the post where you indicated the frequency this j-pole will operate.
If your pervious post about making money by building j-pole antennas for HAM use implies that you think there is a profit to be had by building j-poles, I'd advise you to get the orders first.
Jerry

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Jerry Martes wrote:

have
electrical
j-pole will

antennas for

building
increase
I guess I meant I dont like the look of tarnished copper.
I thought maybe there would be some pocket change selling a few on ebay or something but I dont know how you would ship a j pole. It would be awful long.
I am mainly wanting it for the two meter band and maybe 440. I would like something I could put up and forget about for many years.
If I used 1/2 or 3/4 inch tubing in ss, how could I bend it?
Also, would an antenna made out of emt result in similar characteristics of and identical one made of stainless? Does emt have simialar charactieristics as ss?
As far as the money thing, I wlikme to build things with my hands in my garage and have always wanted to find ways to make some money on the side doing this but I dont have as many skills as a lot of you out there. I have a baby coming any day now and with a family of 4 money is hard to come by! Any of you guys have ideas? I am not wanting to get rich but do something I enjoy on the weekends or so maybe to sell to make some extra money. I always get ideas then talk myself out of it thinking it wont work or someone else talks me out of it.
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x-no-archive: yes
Since most people fab their own antennas from copper tubing, maybe you could come up with some type of bracket to sell that would allow them to easily mount the j-pole to a sidewall, roof, tree or chimney?
I am a HAM & a welder and machinist, most of my HAM friends are more into electronics than metalworking and always asking me to fab crazy shit for them for antenna masts and mounting, etc. Try to think of stuff along those lines?
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snipped-for-privacy@hotmail.com wrote:

Stainless will not work very well compared to copper unless you plate it. Way back when I knew of a guy that plated his 10 meter ss whip antenna. silver over copper over nickel. ( I think he worked for bell labs at murray Hill.) That antenna worked much better than the standard 10 meter whip...
Stainless will get hot with rf flowing through it or along the surface. Ive seen it happen when ss bolts were used on a hi power rf feed through.
John
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I tried building a stainless QFH antenna to pick up weather satellites but the resistance is so much higher than copper that it turned out way off the target 137 Mhz. I ended up with 1/4" hard wall ACR copper and nickle plated it. If you want to try stainless McMaster has 50' rolls of 304 stainless tube that bends pretty well.
--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
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Glenn Ashmore wrote:

A change in resistance will not change the resonant frequency. Resistance will affect the Q and bandwidth.
Kevin Gallimore
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axolotl wrote:

the resisatnce of the stainless is a pure resistance but it is in parallel with the radiation resistance/ reactance causing a mismatch with the transmission line with the associated standing waves. This factor probably caused the off freq tuning since the transmission line became resonant.
John
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john wrote:

We'll have to agree to disagree on this one.
Kevin Gallimore
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snipped-for-privacy@hotmail.com wrote:

Many designers stay away from steel and nickel as antenna materials because they generate passive intermodulation distortion. Probably not a big concern for ham use. Mcmaster-Carr has stainless thinwall tubing.
Kevin Gallimore
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axolotl wrote:

Any bad metal to metal connection can act like a mixer diode and cause intermodulation if other sources of rf are getting picked up by the antenna. Some of the earlier ELT beacons were subject to that type of problem. The adjacent channel signals would go from the antenna into the freq. multiplier diode in the output and mix with other signals and re radiate to cause interference on other channels.
John
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john wrote:

Magnetic materials do not require an additional source of RF to generate intermod because the material itself is nonlinear. A "rusty bolt" diode doesn't need two sources of RF for the same reason.
Kevin Gallimore
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axolotl wrote:

The distortion and nonlinear problems occur when the iron is magneticly saturated. This results in radiation of harmonics of the fundimental frequency. When another signal is present you get intermod products. The sum or difference of the two signals and of any modulation that in on the signals. IF one signal is modulated by a 10kc. tone there wil be a intermod product every 10kc. away from the fundimental signal at diminishing powers.
John
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john wrote:

Well, no. A look at a hysteresis curve as it passes through zero will illustrate this. Google "passive intermodulation" and you can read why you don't use stainless connectors when it matters. But I suspect that I, along with (pick your favorite antenna textbook author)will not be able to convince you of this. So we will again have to agree to disagree.
Kevin Gallimore
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Or read the Trompeter connector catalog.
Most folks who gold-plate connectors use a nickel strike under the gold. Ni, being ferromagnetic, causes problems with IMD on extremely low-level signal lines. Trompeter took great pains to develop a pulse plating process to put down gold on their contacts *without* the Ni strike, to avoid this problem.
I found this out when I was trying to locate connectors with very low remanent magnetization.
I also don't thing that plain copper tubing would work well for an antenna, the skin effect will cause most of the rf currents to flow along the tanished exterior. Solution might be to paint the outside.
Jim
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