N654BA was GPS equipped in 2003 by Banyan Air Service in Ft. Lauderdale, FL. I don't think it would be sniffing radar sites since that is not in the plane's mission.

What is baffling is the antenna is side mounted and on one side, so it won't work very well since at times the plane body will shield the antenna.

In Vegas, they also added two antennas at the back of the plane. I'll dig up the images and post them later.

I wish I had copied one of the links I was digging through yesterday.

The government in Australia was attaching round antennae like the 501 to helicopters and airplanes to dynamically map out wireless communications coverage over a large area.

From what I can remember they were looking at how high wireless 2.4Ghz network hotspots could transmit over different types of terrain. They were also looking at 800-900Mhz as well.

It might make sense given the recent ubiquity of wireless internet and folks running around with wireless laptops.

The only reason I would think that an antenna would be on the side of an airplane is so that it could circle an area and listen.

These guys were talking about using cherry-pickers and helicopters but the cherry-pickers couldn't go high enough and the helicopters were too expensive. They wanted to be at a certain altitude and linger there for a bit to measure signals, then move somewhere else.

Of course it could just be a miniature DirecTV antenna like they are putting on trucks and limousines these days. :-)

finally a topic worth reading, not too much discussion anymore on the janet aircraft.

The only thing that bugs me is that the one antenna is going on the side of the plane.

Maybe the commuters are watching HBO on those long flights!

If it is a wireless service, generally they create a mesh, i.e. transmit from multiple directions, so you wouldn't need the antenna on both sides. [If you did, you would need some sort of diversity scheme to pick the best site.] If you check out this photo
www.lazygranch.com/images/airshows/nellis2007/tbirds23.jpg
[Referring page
www.lazygranch.com/nellis20007_tbirds.htm ]
You can see a few wireless antennas. However, since I can get the Nellis wifi from Las Vegas Blvd, I expect there are transmitters on the far side of the base transmitting towards the street.