Why would you mount a big, thin disc on the roof of your limo?

October 30, 2009 7:07 AM

Did I see the ground-based version of a "black helicopter?"

Okay, driving in to work this morning I saw something on a vehicle that I've never seen before and I'm wondering what it was. This is the DC area, btw, so God only knows what kind of weird government stuff is roaming the streets.

Perfectly ordinary looking black stretch limo, opaque windows. What was odd was a disc-shaped structure mounted on the roof. I only got a quick look at, but it was flat, very thin, and the diameter was about the width of the car. It was mounted on the roof by four brackets that held it just off the roof itself. The disc looked like it had a kind of projecting flange around the circumference, as if it were two pieces. And the whole thing looked like it was maybe three or four inches thick, tops.

So it wasn't some kind of roof mounted storage, unless you maybe needed to take your gong with you. The thing I can come up with that's closest to making sense is some kind of antenna, but then why would it need to be so big? Wish I'd had been on the ball enough to check the plates. So any ideas? What the hell did I see?

posted by Naberius to grab bag (11 comments total)

Some people have been mounting antennas to their cars to get better GPS signals, especially in the downtown areas of cities with tall buildings that can affect reception.

Alternately, some limousines have satellite TV reception.
posted by muddgirl at 7:12 AM on October 30

Was it something like this? If so, I guess it's a satellite TV antenna.
posted by cabingirl at 7:13 AM on October 30

Here's another example of a satellite TV antenna.
posted by le morte de bea arthur at 7:14 AM on October 30

Did it look like this?
posted by zamboni at 7:15 AM on October 30

I think it's a communications antenna. I've seen at least one similar-looking thing on the roof of what I think was an undercover police or other gov't SUV (black, tinted windows, relatively discrete light bars everywhere including integrated into the roof-rack that the antenna was mounted to) on I-270. I wouldn't have noticed, but I was stuck in traffic next to it for a long time, on one of the MTA commuter busses.
posted by Alterscape at 7:16 AM on October 30

Yep, those are all pretty much it. I guess I just thought even satellite TV antennas were smaller than that these days. And that they were far too directional to allow for a simple disc pointing straight up.

Shows what I know. Thanks everyone. Now I'll have to work on a question that takes more than 30 seconds to answer.
posted by Naberius at 7:24 AM on October 30

Well, because it's pointing straight up it follows that it has to be pretty big.
posted by zsazsa at 8:03 AM on October 30

"I guess I just thought even satellite TV antennas were smaller than that these days. And that they were far too directional to allow for a simple disc pointing straight up."

I think that this particular iteration involves some sort of powered LNB/signal receiver which rotates and moves around within that disc in order to remain pointed at the satellite.
posted by iknowizbirfmark at 8:31 AM on October 30

If the "lid" was in two halves could it have been a roof-mounted gatling gun?
posted by alby at 10:41 AM on October 30 [1 favorite]

Well, it wasn't, but I'm now going to pretend that that's what it was because that is so much cooler than a satellite dish.

Holy shit, I saw one of those secret Government war limos out on the street! It was awesome!

Thank you, yes, that is much better now.
posted by Naberius at 11:22 AM on October 30

It's not a simple disc, and there's no rotating part inside the shell. The disc contains phased array of small antennas with a fancy processor that tune in signals from any direction with high precision, and it's good enough to track a geostationary satellite while driving around.

These antennas cost a few thousand dollars, but it's worth it to watch satellite TV while in your jacuzzi shipping cold champagne ... on the freeway.
posted by miyabo at 12:13 PM on October 30