Source for stainless steel tubing (small diameter)

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

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.

wondering

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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?

Why not just use copper pipe? It won't rust. You could weld them up if you don't want to use pipe fittings.

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

A change in resistance will not change the resonant frequency. Resistance will affect the Q and bandwidth.

Kevin Gallimore

Copper is kind of ugly and tarnishes which I would think would increase the resistance over time.

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

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

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

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

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

We'll have to agree to disagree on this one.

Kevin Gallimore

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

Have you had much trouble with copper tubing "rusting"? I have some copper stuff outdoors, and it ought to last MANY years. It may eventually be destroyed by wind, ice or maybe bird droppings & corrosion, but it won't happen very quickly. I think the bird droppings might tear up stainless about as fast.

There used to be an outfit called "tube sales" that stocked thousands of different stainless tubes in all sizes and wall thicknesses. We made custom air heaters for research equipment from thinwall stainless, and that's where we got it.

Jon

electrical

j-pole will

antennas for

building

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.

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?

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

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