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Comment by caseyy | Hacker News Reader

Now shark fins are in vogue again because they house multiple antennas — FM/AM, DAB, GPS, and recently more importantly, 4G. Maybe even WiFi — weird as it sounds, I saw some strings for WiFi antennas in a popular stock media/head unit’s firmware.

Though you are probably right and many cars with just FM/AM and DAB still put them in windshields.

I’m not sure about that 3+ antenna claim for FM. Do a fact-check there. ;) I think most diversity antenna systems that you describe use 2. And they are still considered “premium”. 3 is a bit overkill for FM, FM is very resilient against obstacles.

If I’m wrong, would be interesting to see an example of a car that uses 3 or more. Probably far outside of my pay grade to say the least.

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I'm going by the BMW E90 (Top HiFi option) which has 3 physical FM antennas FM1, FM2 and FM3, all in the rear glass, and a fourth "FM4" which is not a physical antenna but a combination of FM1 and FM2.

They really didn't want you losing signal!

This isn't even mentioning the festoon of other antennas for DAB, mobile (which has a backup too and phones home in a crash: in case the shark fin is broken in a crash)

I could be wrong, but E90 with the best HiFi package is a very rare exception to the rule. I wouldn’t say you often see such configurations.

It’s cool they did that but it’s almost like they are trying to prove some point — maybe to be the best in the market for FM by a hair. :) One antenna is more common than 3 to my knowledge, by far.

Fair enough, I just happened to have an E92 and one day I read all about its systems when it had some major electrical issues :) (Turned out they were due to someone forgetting to clip a piece of harness back in place after some work, and as a result the harness rubbed against something in a wheel arch, eroding the insulation and letting water in intermittently screwing up the CAN bus!)

My (old) E36 BMW had a switched multi-element array in the rear glass that served as the FM antenna.

It had a magic box that used feedback from the stock radio's IF section to (try to) erect the best pattern for good reception at any given time, and which presented one unified RF output to that radio's singular input.

Cadillac has used the same, or very similar, system as well.

Which is neat and all, I guess, but we seem to be getting off into the weeds: These antenna elements were not invisible at all except for the fact that they blended in with the heated defroster elements that were also printed onto the glass.

> WiFi — weird as it sounds, I saw some strings for WiFi antennas

This is probably so the car can act as a Wifi hotspot, with the Wifi antennas located in the interior rather than in the sharkfin.

Sometimes both. My car can connect to my home's WiFi for its software updates. I doubt that antenna is inside the cabin of the car.

It also can act as a hotspot if I bothered paying for its data plan. I'd rather if I could just load an eSIM for my existing service to have it be a hotspot for me. Since its antennas are on the outside it should get way better GPS and cellular connectivity than my phone in my pocket deep in a metal box.

I've seen strings for selecting a WiFi network in an SSID list :) I'm guessing for OTA updates when the car is at home or there is another use that involves your phone's hotspot.

I've seen what you are talking about, too. My VW RNS had settings to use the car's 4G for passenger WiFi.

Cars really want to phone home these days

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