If you have a triplex aerial / antenna, the blue connector is GPS, the white one Fm and the purple one GSM. (I believe)

But where does the GSM one actually connect to?

It will depend what phone kit you have in the car. With the version that is RSAP, the phone actually has it's own transceiver and uses the antenna for that rather than your own phone transmitting. For example in Superb the system does that.

I think the white is used for remote control of the fuel burning heater they have in cold countries as it sems to short for FM. However I'm basing that on guesses, not actual information.

I kind of guessed that, but wasn't sure if it had anything to do with the bluetooth phone kit or not.

Can anyone else confirm any of this?

The shark fins are generally too short for FM reception but might possibly be FM/AM reception as some have a brown connector which might be for that or webasto (heater?). In the case of vehicles with shark fins there are usually radio reception aerials in some window around the vehicle.

Skoda triplex aerials have a shark fin (GPS & GSM aerials) and a 'whip' aerial for FM reception.

Is there a shark fin without a whip aerial that does GPS & FM/AM radio reception without GSM?

For sure there won't be a fin that does AM without any kind of whip. It's all about wavelengths (though technically AM is not a band but a way of transmitting before anyone corrects me).

AM waves are hundreds of meters long so you need a reasonable length aerial or they just aren't picked up. FM is shorter, but still in the range of metres so a shorter antenna works but a very short one is still no good. GSM ones are shorter still, the longest being a few cm, so short antennas are fine, though you can still get better results with a longer antenna if the signal is weak. GPS is extremely short and is received using a patch not even a stick. Remote controls use a couple of different bands, somewhere between FM and GSM.

If you want to know the actual length of the waves in metres, theres a formula:

Speed of light divided by the frequency = wavelength

AM is typically 1MHz, FM 100MHz, remote controls 433 or 868MHz, GSM 900 or 1800MHz, and I don't know GPS without looking it up.

Hope someone finds this interesting, sorry if it's boring!

Just had a scout round the bay.

Only two listings for proper OE fin antennas. One has three connectors, GPS, GSM, Webasto. The other claims to be GPS and FM, but from the connector colours I'd be pretty certain its GPS and GSM really.

Think I might have had that second one - and returned it as it was misdescribed (condition as well as useage). At least seller gave me money back and covered my return postage costs so I didn't lose out.

Thanks for the info on wavelengths - how does the VW Touran (for example) have no roof aerial and two identical window aerials - one for FM only and the other for FM/AM (the amps are marked accordingly but the pattern of wire on the glass is identical) if the wavelengths are significantly different?

I don't understand these things, so I'm looking for a basic explanation if you wouldn't mind.

Generally you try to match the length of the aerial to 1/4 or 1/2 a wavelength. 1/2 is better than 1/4. Now thats OK for FM and the shorter ones, but you just can't get an antenna big enough to do AM waves as the glass, well actually the whole car isn't near

big enough when the wave is hundreds of metres long. So they just transmit a higher power, and make do with the best aerial you can. The biggest aerial happens to be about right for FM, so it's used for AM too because you can't make it any longer. Saying that many cars do have a difference between the AM antenna and the FM one(s) though clearly not all.

If you think about it it's always been this way, even with a simple rod aerial. It about matches FM frequencies, but is used for AM because it's not sensible to have one that matches AM properly.

That's a great basic explanation - thank you.

So basically - don't worry about AM reception as it's never going to be any good without a very long aerial!

Yep. pretty much. Submarine communications sometimes use the real lower end of the frequncy, below even the AM band we call Long Wave. They tow dirty great cables behind them to receive these signals underwater. Or at least they used to, may have been superceded these days. The transmitting aerials are fairly long too. Great example at Wychbold near Droitwich. Two towers, with the aerial strung between.