AMOS antenna messing sheet

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Try:

which is the same article cleaned up for publication in Antennex.

The "messing sheet" should be "meshing sheet", which is the rear reflector.

Just about anything can be used for the rear reflector. My first model was a pine 2x4 with aluminum duct tape stuck to one side. The reflector width has a big effect on the horizontal beam pattern and front-to-back ratio. Wider, is generally better. The article uses 5 wavelengths wide.

Mesh is fine for a reflector. I'm not sure how many wires are needed. My guess is 8-10 wires per wavelength is a good minimum. Please do

*NOT* use non-welded wire mesh as each crossover junction will make a wonderful diode junction when wet. If you must use mesh, use welded wire.

Incidentally, the reflector on the AMOS-5 is about 36 wavelengths long. At 1.2GHz, that's about 36 inches long.

Well, so much for the dimensions in the article. The drawing says 455 x 62mm for the reflector. 62mm is 5 wavelengths wide which is obviously wrong. The bottom of page 2 says: The reflector is very narrow, 0.5 wavelengths, so that it narrows the horizontal radiation diagram as little as possible.

0.5 wavelength would be 6.25 mm, which methinks is the correct width,

Argh. 62.5mm is the correct width. I managed to get mm and cm mixed up (again).

I either need a vacation, a new calculator, or I should not be trying to do anything useful at 6AM.

As always, thanks for your help. I scaled the antenna in open office calc using 2445/1090. Since there is no ohmic contact to the reflector, the Al tape sounds like a good idea. Another might be to use lexan from Tap Plastic and spray it with a conductive paint. I recall seeing an article regarding spraying a FTA dish to improve the reflectivity. I have the spray paint used for shielding RF, which I think is nickel.

If the single antenna worked well, I'll try the back to back scheme. The application is for mode-s (aircraft) reception, and it turns out that the AMOS 5 has a nearly perfect "squished donut" for the application. That is, the gain is strong on the horizon and with elevation. The situation is similar to LEO antennas, but the reception on the horizon is more critical that satellite application.

Mechanically, the support for the wire would be better if at least one of the wire segments that was higher above the ground plan was supported by the coax dielectric. I suspect the wire at the edge could be supported since it would be the point of zero antenna current. What I am getting at is the wire could rotate if supported as shown in his diagram.

You're sniffing transponder codes? Methinks a discone or trunstile would be more appropriate as you need hemispherical coverage.

I never really tested how good it worked, but it looked ok. I'm trying to cheat a few customers so I have some spare change to buy a new reflection coefficient bridge and sweeper so I can test antennas.

Barf. It's the surface conductivity that's important. Most of the surface is so borken up that the conductivity will suffer. The reflector is going to be 14cm wide (5.5 inches) wide. That's too wide for aluminum duct tape. Find a sheet metal shop and get a strip of aluminum that's the right width.

Barf 2.0. The wire grid inside a fiberglass pizza dish is about 1mm below the surface. If you paint over it, the focus will move or distort. A typical 18" DBS dish is better as it only has a layer of paint on the surface. However, the net gain improvement by improving the dish reflectivity might be perhaps a few hundreths of a dB. Not worth the effort. As long as the reflector material is not dissipative (i.e. carbon graphite base paint) the gain from a shiny, dull, steel, aluminium, mesh, solid, whatever, are about the same. There's some loss due to a grid (barbeque grill) arrangement, but even that is fairly small.

Ok, but what about directly overhead? What about polarization sensitivity? Look into the various circularly polarized antennas used for GPS for a hemispherical pattern.

You can easily do that. If you use a aluminium sheet for the reflector, just swage a brass rivet into the coax hole and solder the coax braid to the brass rivet. I also have a PCB balun design that looks useful as the tiny balun is a pain to make consistently the same.

I didn't optimize the values for the AMOS-5. Running the AMOS-7 through the 4NEC2 optimizer took the better part of a weekend. The results were worth it. 14dBi gain. I can do the same for any configuration, but don't have any time right now (yet another medical problem). Good luck.

Incidentally if you're decoding Mode-S:

See TSO-C74c:

2.1(a) The receiver nominal center frequency must be 1030 MHz.

2.10 Reply Transmission Frequency. The center frequency of the reply transmission must be 1090 ±3 MHz.

By the unique 24 bit encoded aircraft ID in the reply preamble.

How it works:

European version:

Their monitoring project ran into some anomalies, most of which have been fixed:

Meanwhile, in the US, they're slowly pulling the plug on TIS sites:

If you want/need congestion data around the major TCA (tower controlled airspace) areas, Mode-S is still a useful feature.

Some airports have online displays of their traffic data, some of which are TIS based.

(Run page and wait about 30 seconds for the display to appear).

The nifty feature of Mode-S monitoring is the TIS (traffic info service) available on some glass cockpits (i.e. Garmin G1000) which displays a TIS data overlay on top of the moving map display. Some transponders include traffic displays. For example:

I sorta blundered across this project... It's a G1000 glass cockit emulator for MS Flight Simulator:

I think it will work with Wideview and Project Magenta simulators but I'm not sure. It kinda looks like a stand alone unit, even with the CAN-BUS:

Anyway, the TIS (and WX) data would overlay the traffic map shown in the lower photo on the glass-cockpit.org home page.

I want one...

(4 pages)

This is all very well with only one aircraft for a home user to track but given the area he intends to cover there are bound to several aircraft and I would like to know what equipment he is going to use. Unless he has a licence agreed by the FAA he is going to have to rely on SSR's to activate the beacons and I am curious as to how he is going to align the other data, non-id data, to an aircraft.

There are two manufacturers of mode-s receivers for hobby use. Kinetics and Airnav. What you need to consider is how many are squawking at one time. You are most likely going to receive planes interrogated by maybe two or three FAA sites at most. The FAA paints the planes with a narrow beam, so there are not a lot of signals active. You can prove this to yourself with just a scanner tuned to

1090, preferably on AM if your scanner supports it.

If you dig around the net, you can find websites of folks who have bought used cockpits to integrate into their home flight simulators. I haven't found any projects with hydraulics to move the plane around.

Incidentally, you couldn't give me anything from Matrox. That company screwed me with some vaporware. I bought a card that indicated it could do something, but that features ended up being just a promise to be implemented, and it never happened. Worse yet, you had to call Canada on your dime. Email went into the infinite bit bucket. ATI, now part of AMD, are the good Canadians, though the last system I built using integrated Nvidia graphics due to some complaints about ATI on the net.

So are you OK with copper flashing for the reflector?

Interesting, never seen those before. I thought you were building your own system. The problem with using a scanner where I am is we do get quite a few military aircraft on training ops so they do use the other modes and we are also on the "Oceanic" route for transatlantic flights so there is quite a lot of traffic at different times of the day. In another lifetime, nearly 30 years ago, I worked on the SSR1500 series of transponders.

Oh, I looked into being mine own years ago. Not impossible, but quite a lot of work. Even if I could get the hardware working, I'd have to open source the hardware design to get someone to do the software.

Sure, but copper is expensive overkill. I suggest aluminum with a brass grommet for soldering to the coax braid.

Looking back at the article, it seems the ground plane floats, so you don't need to connect it to the coax braid. Or did I miss something. If I need to connect to the ground plane, then copper is probably the way to go. Otherwise the connection corrodes. I've built antennas out of Al and used the dielectric goop from the hardware store, which works for a while, but ultimately the connection goes bad.

It can either float or be grounded. I've seen it built both ways. I haven't tried tweaking the model to be sure, but my astute guess is that it doesn't matter because the balun eliminates all radiation from the coax shield. For example:

shows that it's grounded. That's also the way I like to do it because of the added mechanical rigidity.

I can see you've never tried to solder to a giant copper heat sink. I had to use a propane torch with a huge copper soldering tip in order to generate enough heat to solder to copper sheet. Worse, I was soldering the copper directly to the coax braid. By the time I got it hot enough to melt solder, there was enough heat saved in the copper to melt the dielectric. The nice thing about the rivet trick is that the thermal connection between the brass rivet and the aluminum heat sink is minimal. Therefore, the heat stays in the brass rivet and it solders easily.

Hints for aluminum (from experience with designing marine radios for about 9 years).

1. Don't use stainless and aluminum. Use ugly hot dipped galvanized screws. Those are the dull gray colored screws, not the shiney ones.
2. Wash the aluminum in vinegar before painting.
3. Forget about dielectric goop, contact cleaner, silicon grease, and other crap in the connector. Mate the connectors dry and do whatever is necessary to waterproof the connector. I mummify the connectors in PTFE tape followed by a layer of Scotch 66 electrical tape. I recently disassembled a connector pair that's been on a tower near the ocean for about 8 years. The connector guts were perfect, but the crappy copper plated clamps rotted through the jacket and trashed the coax.
4. Copper corrodes into copper oxide, sulphate, sulphite, etc all of which are lousy RF conductors. The elegant copper patina is useless for RF. If you must use copper outdoors, invest in a silver plating bath and plate it. The sliver will turn dark (silver sulphate) but conducts RF even better than shinny silver.

Well, if I can float the ground, I'll go Al foil on plastic. I will first see what the Al Rem Center in Santa Clara charges to cut some Al plate to size. Or I may get lucky and find some Al the right width and longer than needed, then just hacksaw the along the short direction. I don't know if you ever bought metal there, but these guys are busy. I think the walk in sales are a minimal part of the business.

I have soldered to copper plate, and it is a PITA, though not impossible. I built one of those biquad wifi antennas. I tinned the copper first. When soldering the N female jack to the copper, I put a sacrificial N male plug into the jack. This kept the center pin from moving around.

Isn't there a dissimalar metal corrosion problem between brass and aluminium ?

Yes, brass and aluminum hate each other. It's the zinc in the brass that's the problem. I forgot to supply an important detail. You have to solder plate the brass rivet.

See:

Start with 6061-T6 sheet aluminum and go down the table until you find something that's solderable. The first is tin followed by solder plate. So, I take the brass grommet, solder dip it, pound it into the aluminum, and it seems to last. I would use tin grommets but I've never been able to find any.

Copper is much better than brass, but tends to be more expensive and hard to find. Brass grommets can be found in most camping supply stores as tent and tarp reinforcement. They usually include the necessary tools.

Typical consumer eyelets and grommets:

Grommets for large coax cables and eyelets for small holes.

When you mentioned rivets I was thinking more in line with these:-

I couldn't really see how plating these would work considering that the surface would probably stretch when hammered. The dissimalar metal question, Brass/Al, popped up recently for me when doing some work on the car, mentioned in another thread, and I was going to be cheapskate and use some materials to hand rather than purchasing new.

Oops. Sorry. I should never have mentioned rivets. It's grommets and eyelets instead.

Certainly not for rivets. However, solder is rather mallable and pounding on it will not expose any base metal.