I think the thread author is referring to the devices that receive a signal from an item of audio equipment - ie from the headphone jack of a discman or MP3 player for example - and then transmit a very weak FM signal to allow your car radio to pick it up.
This allows you to listen without having to fiddle with wires or take the head unit out of the dashboard to tinker.
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I might add that in a previous company car where I was not allowed to replace the standard fit cassette/radio with a cd/radio, I solved the problem by using a dummy cassette with a flying lead plugged in to a discman headphone socket.
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Maybe the OP could clear it up for us. I don't imagine any weak signal is likely to be illegal, though.
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If you don't have a AUX input on the car audio system, the simple way of getting an external MP3 player to play through it is to hang a transmitter off it. You then tune the radio into the appropriate frequency and then you can listen in glorious stereo.
It works in theory, however I tried a unit that simply sits between the radio and aerial (so I suspect is not illegal as no external transmission should have been made), but the results were less than ideal.
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I know of an offspring who imported a few IPOD transmitters from the USA for him and his friends. IIRC it is a little unit about the size of a lipstick case that plugs onto the IPOD. Then as stated it requires the FM radio to be tuned to its frequency to listen to the IPOD tunes.
It seemed to work well.
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Sorry for not being very precise with my query.
Basically as henry k mentioned, its a small bit of kit that has a line that connects to the headphones socket of your Pda/mp3 player and transmits whatever you want to hear to your car radio, so that you can hear them on your car stereo.
Its fairly common in the USA , although I dont personally know anyone who possesses these, so unable to establish just how good these actually are.
Uk laws forbid any transmission in the FM requency regardless of its size/power.
I have tried what SjB {P} has mentioned i.e the cassette with the lead attached t it , but its a awfull tangle and a big mess to set up,compared to these transmitters.
Its just the legal bit that worries me, because thats one reason for the friendly cop to catch you,even if he couldnt find anything else wrong!
This is one of the products I was referring to
(Hope the link works!)
catalog.belkin.com/IWCatProductPage.process?Mercha...3
What would you think about this and whether these things really do work?
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I wouldn't worry. The signal is so weak anyway that the chance of it being picked up is negligible (and in any case how many cops carry FM detectors?!) A friend of mine has been using one of these devices for years (since 1990 or so) without problem.
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Belkin are a very reputable company so I see no reason why they shouldn't work.
I'd go ahead. As the output is so low it won't create much interference, unless you have a vehicle very close to you with the radio tuned to the same frequency.
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Some general notes that might be of interest::
The terminology here is a little bit adrift. FM stands for frequency modulation and relates to how the audio signal is being modulated/encoded (the frequency is changed slightly) on to a radio frequency that is being used to carry it. FM is used because it provides for a good quality (low noise) music signal to be recovered at the other end provided the modulation is done right in the first place. Thus most radio stations use it.
So what you are asking about is the legality of transmitting a radio signal.
Strictly this is illegal except from approved devices on their particular allocated frequencies and within their power rating. This is because if it were really a 'free for all' the situation would descend into chaos with powerful transmitters competing for air space.
Non-licensable equipment usually has a very low power output like one thousandth of a Watt or less, (with the exception of mobile phones) and the equipment has to be submitted for approval before getting a licence to manufacture it, and it is not to be modified in manufacture without re-submission.
Having said that, if no one is aware that you are using a transmitter, perhaps because it is of such low power as to be difficult to be picked up by anyone else, you are unlikely to come to grief. Get a friend to see how far away he can pick up the signal in his car.
Of course, if the transmitter went faulty and transmitted on a police frequency and plod's car was close by, it could be interesting.
I know of a radio amateur who set off a couple of burglar alarms while (legally) transmitting but when plod rolled up to investigate he decided to do the honourable thing and tell him the cause.
Finally, there used to be a similar device you could plug into the back of your video player so as to be able to watch tele. in other rooms. I don't remember any legal actions on individual users although the manufacturer probably got done.
And bugging devices are likely to be illegal with their frequency!
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These things are listed on Ebay in vast numbers at prices in the range £10-20. I bought one in early July to use with my IPAQ PDA (to play mp3's). The RF output power is very low - so the signal is only receivable up to a couple of metres away from the car. Stictly speaking they are illegal though.
I was not impressed with the sound quality of the one I bought (very poor) so basically I haven't used it.
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The specific unit I referred to for an IPOD was
tinyurl.com/rfd4
An interesting unit that plugs into your radio.
www.ipod2car.com/
A Google search, non UK specific, for IPOD transmitter throws up 100K plus hits.
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Finally, there used to be a similar device you could plug into the back of your video player so as to be able to watch tele. in other rooms. I don't remember any legal actions on individual users although the manufacturer probably got done.
Well, I brought one last month from Maplins. On offer for about thirty quid, I thought it worth a punt - just to escape Dawson's Wretched Creek alone it was worth a punt, actually - and it works a treat! Works on 2.4GHz though, which I guess is all legal and above board.
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I think most home appliance devices work on 2.4GHz - doorbells, video senders, (wireless networking?), home automation devices. I'm sure they are legal
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>>Finally, there used to be a similar device you could plug into the back of your video player so as to be able to watch tele. in other rooms>>
You can still buy them - one brand name is Rabbit.
Re wireless frequencies. Wi-Fi is becoming ever more popular both in the home and for picking up "hot spots" outside.
Among the benefits of being able to use a laptop, for instance, anywhere in your property, it also allows loading your music files on to the laptop and be wirelessly available on your stereo, in yourcar or an MP3 player whilst jogging.
As already pointed out, broadcasting is in the 2.4GHz spectrum and most commonly used standards are 802.11b and 802.11g.
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The points about 2.4gHz are all very well and valid but may confuse the original poster into thinking he can use such transmitter into his 88-108mHz receiver. It ain't so!
Best bet, if it's tunable, is to use a frequency at the top end of the radio's tunable range.
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