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Spray painted Patch Antenna

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I am building the GP Patch Antenna (Goof-Proof Patch) and I am wondering if spraying them in Black paint would result in decrease in performance. I will be using three of them at the same with three different Airwave frequencies. Is there any restrictions as to how apart they must be as a minimum? And do I have to rotate the 2nd and 3rd with respect to the first antenna? Any help would be greatly appreciated. Thanks

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I am wondering if spraying them in Black paint would result in decrease in performance.

Painting is generally not recommended.

Is there any restrictions as to how apart they must be as a minimum?

With most wireless A/V systems, normally at least one empty channel is needed between the chosen transmitter channels. But, YMMV.

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Is it possible to feed three receivers set at different frequencies from ONE Patch Antenna??

Edited by timecare

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It is possible, but requires precise matching networks and other critcal design.

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Thanks Mr RC-Cam. Any thing I can look for and find somewhere? I mean I pay for it.

Edited by timecare

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I'm just wondering, what effect would painting have exactly? Suppose you paint the two panels prior to putting the antenna together, what would be the negative aspect of that paint? I can see it functioning as a dielectric between the two panels and the air. Normally the air would be the sole dielectric between the panels. Anybody care to give a solid explanation why it would give a negative effect?

Cheers,

Sander.

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I'm just wondering, what effect would painting have exactly?

Thats the problem, there is no way to tell how the paint you have will effect the patch. If you make a patch and test it then paint it and test it again you may find it better or worse than before, there is no way to know. Often the effect is not big but thats the risc you take.

Anybody care to give a solid explanation why it would give a negative effect?

The electric currents travel over the surface of the plates so anything on them will effect the speed, thats why the plates in the military aerials are silver plated. You may find that reducing the size of the plates will redress the balence of painted plates but testing is the only way to know by how much.

Thanks Mr RC-Cam. Any thing I can look for and find somewhere? I mean I pay for it.

If you find what you want it will be expensive and also loose some signal, separate patches would be much better.

Terry

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Terry,

Well, currents only travel through conductors, and I don't plan on using conductive paint. As per the skin effect I will agree with you that at 2.4GHz the currents will travel at the surface of the plates mostly, I just don't see how a light coat of paint will mess that up.

Mind you, both aluminum and copper will oxidize over time, just by being exposed to the outside atmosphere, creating a thin oxide layer across the surface. Both aluminum and copper oxide are non-conductive. Silver coating would not have that drawback, as silver oxide is conductive, so if that's used for militray patches I can see why.

Cheers,

Sander.

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Any thing I can look for and find somewhere? I mean I pay for it.

I don't have any sources. If your goal is to achieve the best performance, then use separate antennas.

Well, currents only travel through conductors,

Currents even travel through air. :)

I just don't see how a light coat of paint will mess that up.

If the materials used in the paint are completely microwave transparent, and the layer of paint you apply is sufficiently thin to not impact the patch's air dielectric, then it should not adversely affect the antenna's practical performance. Otherwise, I recommend the galvanized metal spec'd in the GP patch project. If it rusts or tarnishes after years of use, then splurge on another $2 piece of roofing tin and make a new one.

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Currents even travel through air.

EM waves do, currents don't :)

Cheers,

Sander.

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EM waves do, currents don't

I just saw lightening hit a power pole this week; Big currents are definitely flowing in the air near me (I didn't say vacuum). The point is, the conductive medium does not need to look like a traditional metallic pathway. A few stray molecules with easily freed electrons will do fine.

BTW, the original comment was tongue in cheek. Sorry for the distraction. :)

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Ionized air indeed conducts, and of course you'll see current leakage from air, eps. in a humid environment, but in terms of magnitude vs. the conductivity of alu or copper that the patch in made from this is not significant <pulls tonque of out cheek> B)

Cheers,

Sander.

Edited by ssassen

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Since we are bantering on this distraction, I would like to say that magical highly conductive paint (i.e., similar to copper) should not impact the patch antenna. It appears to me that it would just create thicker metal elements. As long as the dielectric distance and element size was maintained, things should work out.

However, performance may degrade if the paint absorbs microwave energy or a thick coating changes the dielectric behaviour. That is why we don't recommend shooting a coat of paint on the GP Patch antenna. Maybe one day someone will test a couple popular brands of spray paint and report the measured impact. I expect it will be minimal (or non-existent), but until it is measured I won't recommend the practice.

Keep in mind that some folks have reported microwave signal losses through things as innocent as heat shrink tubing and plastic coverings. My usual fatherly microwave advice is that Everything Matters.

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Yep, the bottom line is that the effect of anything added is a risk. I made some dipoles that were almost a perfect match until I added the heatshrink, now I heatshrink them before I trim them ;)

Terry

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Hello, I'm brand new here.

Does a plastic cover (to enclose the antenna) effect its performance? Like all those ones for sale out there.

Also, how does one get more (higher) gain from a patch antenna? Or, better put, can a guy just upscale the pattern and make one say twice the size as the "Goof Proof Patch" and get more out of it?

Thanks!

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Heh heh. Been following this post and learning lots by the bantering. :) I love this site. :P (Tongue on chin)

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I would suggest that paint, spray or otherwise, that is invisible to microwaves is not usually found in the paint department at Home Depot or Radio Shack......

Now radomes and antennas can be painted and often are, but unless you're using TWT tubes or Magnetrons, I wouldn't recommend it either...

It's one thing with a 50kw ERP radar set and quite another when speaking in miliwatts and DBs...

I will say that it is customary to put on a light coat of lacquer (spray) to protect an antenna from corrosion on lower band ham antennas, but we usually stop treating them with anything at around 220 mhz.

Edited by W3FJW-Ron

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I would suggest that paint, spray or otherwise, that is invisible to microwaves is not usually found in the paint department at Home Depot or Radio Shack......

Now radomes and antennas can be painted and often are, but unless you're using TWT tubes or Magnetrons, I wouldn't recommend it either...

It's one thing with a 50kw ERP radar set and quite another when speaking in miliwatts and DBs...

I will say that it is customary to put on a light coat of lacquer (spray) to protect an antenna from corrosion on lower band ham antennas, but we usually stop treating them with anything at around 220 mhz.

Easy way to find ot the paint/Laquer is absorbing microwaves.. spray some on a piece of paper, let dry then stick it in a microwave, if the paint feels hot when removed it's no good.

I use Acrylic laquer, not seen any problems with power reduction.

Steve

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Also, how does one get more (higher) gain from a patch antenna? Or, better put, can a guy just upscale the pattern and make one say twice the size as the "Goof Proof Patch" and get more out of it?

That would reduce the resonant frequency by half. i.e. 1.2gc. Now if 4 of the original patches were built and phased properly, it would (almost) be the same thing as making it twice as big in the X and Y axis and keeping the same dim.in the Z axis and wind up with 4X (8X?) the gain over a single patch if the world were perfect. In actuality the loss in the connectors and phasing lines at these frequencies would probably negate a lot of the theoretical gain expected. How much I have no idea as it's been 30 years since I built any UHF gear, but it seems it was much harder back then (test equipment not available to the ordinary hobbiest).

Edited by W3FJW-Ron

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Going back to the plastic housing question...

I'm guessing that decasing a 2.4 GHz half-dipole (removing the plastic shell) is a bad idea, in terms of tuning?

Also, (complete RF neophyte) exactly what equipment is required to tune an antenna? I'm assuming it's appallingly expensive?

~Luke

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Removing the housing will only change the tuning a tiny bit, not worth worrying about.

Yes the equipment is a bit expensive, not an option unless you intend to do lots of aerial making.

Terry

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Ok, thanks!

On a slightly different topic, how sensitive are these video links to less-than-perfect SWR?

I'm thinking of trying a DIY GP antenna (see here: http://www.yb2normal.com/antenna3.html) but I definitely don't want to fry the Tx, and since I don't have a SWR meter, I can only assume that since other people have built/used it, it must have a 'safe' SWR...

~Luke

Edited by Luke

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Unless you have the proper equipment for measuring SWR at those frequencies which most everyone doesn't outside of EEs working in the RF field, You'll just have to give it a try. You won't fry the TX as I'm almost sure most of those modules will shut themselves down given high SWR. If you are accurate with your dimensions and fabrication you shouldn't have any problem.

PS: Delete the bracket ) on the end of your link..

Edited by W3FJW-Ron

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Thanks, fixed the link.

The half-wave dipole seems to work well, sans plastic housing, so I'm sticking with that for now.

By the way, how does polystyrene foam rate for (lacking the proper term) 'microwave transparency', relative to say, Teflon or (dry) wood?

~Luke

Edited by Luke

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