Satelite Watching

No, it's not the side lobes as much as the gain dips as you sweep elevation, i.e. starting from the horizon and going to vertical. Mode- s is very different from your typical point to point comms. You need coverage at all elevations. Perhaps I'm not explaining this well. Maybe vertical plane is a better term. With mode-s, the targets are

3D. All around you, plus up and down. It is like satellite reception, only worse since you want to cover horizon to horizon.

Think of the Lindenblad antenna, but with more gain.

The FAA has played with these, as shown in the article, but I've never seen one at an airport. The Lindy has the advantage in that it's circularly polarized. The mode-s transmitter is on the belly of the bird, so you would think it's vertically polarized, but unless you want a lot of angry passengers, you tend to fly level to the earth. So distant plane's antenna would appear to be tilted from the distance observer.

There are stacked Lindenblads, but I'm pretty sure that can't be done strictly passive. There is also that variant of the J-pole that has circular polarization, which broadcast FM sometimes uses in stacks.

All that said, my gut feeling is parallel the 3 element inverted Amos will probably do the trick. The stock antenna, which is 3dbi at the horizon, does 200nm. A receiver is at best only a few thousand above average terrain. The last time I did the math, I got a line of sight to the highest flying plane of about 330m. Using a square law relationship, that means a linear increase of about 2.7., or 4.3db. OK, make it about 7dbi.

Figure 12 shows nearly 11db for the 3 dipole inverted amos.

I understand that, at one time they were docked with each other. Mike

Humor would have been if he removed the compass needle from the brass case.

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The movie \'Deliverance\' isn\'t a documentary!

=46rom a quick calculation, that 1 degree difference in right ascension is about 75 miles.

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I finished reading "Blank Sots on the Map" and one of the chapters covered objects not in the NASA elements.

Really good stuff.