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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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 Posted: Thu Jul 13, 2006 10:03 pm Post subject: |
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| Eldar wrote: | | I'm a professional RF engineer with over 15 years experience in GSM, GPS and satcomms, please, please trust me - I know what I'm talking about. |
OK, I don't doubt that you know your radio theory (it's been 20 years since I did my radio theory exams) but suggesting that a low power FM transmitter like an iTrip will interfere with emergency services radio systems is laughable. 
Perhaps you haven't used one of these iTrips - they transmit a few milliwatts and have a range of about 10 feet (and that's with a clear line of sight). I'm sure you can overdrive the thing and distort the hell out of the transmitter but because the power levels are so low it's unlikely to interfere with anything important.
Let's keep this in perspective eh?
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mikealder
Pocket GPS Moderator
Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs
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| Posted: Thu Jul 13, 2006 10:26 pm Post subject: |
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| Skippy wrote: | | Perhaps you haven't used one of these iTrips - they transmit a few milliwatts and have a range of about 10 feet (and that's with a clear line of sight). |
Not quite true, I recently did an experiment with an FM transmitter and achieved a range of in excess of 300 feet, so the power level to Tx from one car to another is sufficiant to cause interferance, fitting a longer audio input lead gave the device an increased range - not a good idea, the illegal unit is no longer in use I should hasten to add, the car no longer emits any RF as I use an FM injection unit instead which switches the aerial out of circuit releasing it for the TMC reciever (when it comes out) - Mike |
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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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| Posted: Thu Jul 13, 2006 10:31 pm Post subject: |
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| mikealder wrote: | | I recently did an experiment with an FM transmitter and achieved a range of in excess of 300 feet |
Ok, my experience is with one of the iTrip devices which plugs right into the top of the iPod so you can't use a long lead. My iTrip is lucky if it goes more than about 10 feet!!! Maybe it's knackered. :x
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Eldar
Pocket GPS Moderator
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Joined: Sep 24, 2004
Posts: 1294
Location: London
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| Posted: Thu Jul 13, 2006 10:59 pm Post subject: |
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| Skippy wrote: | | Eldar wrote: | | I'm a professional RF engineer with over 15 years experience in GSM, GPS and satcomms, please, please trust me - I know what I'm talking about. |
OK, I don't doubt that you know your radio theory (it's been 20 years since I did my radio theory exams) but suggesting that a low power FM transmitter like an iTrip will interfere with emergency services radio systems is laughable.
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May I point out that the RF power radiated from TomTom GO motherboard is even less, yet it does interfere with the GPS signal. How do you know that something else in this device is not  out the RF at the level which might be perfectly acceptable in the USA, but not in the UK?
You see it might be OK to use these transmitters, but the point I'm trying to make is that I don't know that, if you think that you know better, that's fine by me. |
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carl_w
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Joined: Mar 13, 2004
Posts: 242
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| Posted: Thu Jul 13, 2006 11:38 pm Post subject: |
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| Eldar wrote: | | There are ways of changing the legislation, for instance a number of years ago radar detectors became legal as a result of a court hearing. |
Well not actually. What happened is that it was proved in court that the police were applying the legislation wrongly. IIRC they were catching people for "interfering with a police transmission", when in actuality a radar detector is just a receiver that operates on the appropriate band, hence falls into RA/Ofcom's class of "receive only" equipment. No "interference" took place. |
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carl_w
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Joined: Mar 13, 2004
Posts: 242
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| Posted: Thu Jul 13, 2006 11:41 pm Post subject: |
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| mikealder wrote: | | the car no longer emits any RF as I use an FM injection unit instead which switches the aerial out of circuit releasing it for the TMC reciever (when it comes out) - Mike |
Why would you do this instead of rigging up a line-in? The FM injection unit thingies seem to cost as much as a proper solution like the iceLink, and the audio quality is nowhere near as good. |
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mikealder
Pocket GPS Moderator
Joined: Jan 14, 2005
Posts: 19638
Location: Blackpool , Lancs
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| Posted: Thu Jul 13, 2006 11:58 pm Post subject: |
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| carl_w wrote: | | Why would you do this instead of rigging up a line-in? The FM injection unit thingies seem to cost as much as a proper solution like the iceLink, and the audio quality is nowhere near as good. |
I agree but if you have a costly deck in the car that doesn't have the line in connection you have to improvise, the injection unit releases the FM aerial to do other things (TMC springs to mind) auto switched from the TT Go-910, when they release the module I will explain how - Mike |
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Eldar
Pocket GPS Moderator
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Joined: Sep 24, 2004
Posts: 1294
Location: London
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| Posted: Fri Jul 14, 2006 12:03 am Post subject: |
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| carl_w wrote: | | Eldar wrote: | | There are ways of changing the legislation, for instance a number of years ago radar detectors became legal as a result of a court hearing. |
Well not actually. What happened is that it was proved in court that the police were applying the legislation wrongly. IIRC they were catching people for "interfering with a police transmission", when in actuality a radar detector is just a receiver that operates on the appropriate band, hence falls into RA/Ofcom's class of "receive only" equipment. No "interference" took place. |
Well, yes actually. The legislation was applied exactly because a radar detector is a receiver.
"Microwave radio emissions from police radar speed guns did not constitute a "message" for the purposes of section 5(b)(i) of the Wireless Telegraphy Act 1949, even within the extended meaning of "message" given by section 19(6).
Accordingly, the use by a motorist of an electrical field meter to detect the presence of such emissions was not an offence under section 5(b)(i) since the device was not used "to obtain information as to the contents, sender or addressee of any message.
Section 5 of the 1949 Act, as amended by section 3 of the Post Office Act 1969, provides: "Any person who - . . . (b) otherwise than under authority of the [Minister of Posts and Telecommunications] or in the course of his duty as a servant of the Crown, . . . (i) uses any wireless telegraphy apparatus with intent to obtain information as the contents, sender or addressee of any message . . . shall be guilty of an offence. . ." |
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carl_w
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Joined: Mar 13, 2004
Posts: 242
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| Posted: Fri Jul 14, 2006 12:07 am Post subject: |
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| Eldar wrote: | "Microwave radio emissions from police radar speed guns did not constitute a "message" for the purposes of section 5(b)(i) of the Wireless Telegraphy Act 1949, even within the extended meaning of "message" given by section 19(6).
Accordingly, the use by a motorist of an electrical field meter to detect the presence of such emissions was not an offence under section 5(b)(i) since the device was not used "to obtain information as to the contents, sender or addressee of any message.
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OK, so I was wrong on the details. But the principle still holds. The law was not "changed", a clarification as to its implementation occurred through the act of setting precedent in court. Effectively the law was that way all along, it's just that it had never been tested properly in that context until that case. |
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carl_w
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Joined: Mar 13, 2004
Posts: 242
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| Posted: Fri Jul 14, 2006 12:09 am Post subject: |
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| mikealder wrote: | | I agree but if you have a costly deck in the car that doesn't have the line in connection you have to improvise |
I guess I can't really preach -- whilst I got an IceLink installed in the wife's BMW (it integrates really well with the display and everything), in my TVR I have a crappy Pioneer head unit with one of those tape iPod interfaces. Fortunately the exhausts are louder than the noise of the cogs in the "tape" whirring around. |
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Eldar
Pocket GPS Moderator
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Joined: Sep 24, 2004
Posts: 1294
Location: London
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| Posted: Fri Jul 14, 2006 12:19 am Post subject: |
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| carl_w wrote: | | Eldar wrote: | "Microwave radio emissions from police radar speed guns did not constitute a "message" for the purposes of section 5(b)(i) of the Wireless Telegraphy Act 1949, even within the extended meaning of "message" given by section 19(6).
Accordingly, the use by a motorist of an electrical field meter to detect the presence of such emissions was not an offence under section 5(b)(i) since the device was not used "to obtain information as to the contents, sender or addressee of any message.
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OK, so I was wrong on the details. But the principle still holds. The law was not "changed", a clarification as to its implementation occurred through the act of setting precedent in court. Effectively the law was that way all along, it's just that it had never been tested properly in that context until that case. |
OK, you win - I was wrong all along, you can't change the bloody legislation in this fascist state, you can only prove that it is applied incorrectly. |
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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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| Posted: Fri Jul 14, 2006 1:41 am Post subject: |
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| Eldar wrote: | | How do you know that something else in this device is not out the RF at the level which might be perfectly acceptable in the USA, but not in the UK? |
Because it's CE approved and Directive 1999/5/EC states that a condition of CE approval is that radio equipment shall be so constructed that it effectively uses the spectrum allocated to terrestrial/space radio communication and orbital resources so as to avoid harmful interference..
I can sleep easier now that I looked that one up.
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Eldar
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Joined: Sep 24, 2004
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Location: London
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| Posted: Fri Jul 14, 2006 9:32 am Post subject: |
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| Skippy wrote: | | Eldar wrote: | | How do you know that something else in this device is not out the RF at the level which might be perfectly acceptable in the USA, but not in the UK? |
Because it's CE approved and Directive 1999/5/EC states that a condition of CE approval is that radio equipment shall be so constructed that it effectively uses the spectrum allocated to terrestrial/space radio communication and orbital resources so as to avoid harmful interference..
I can sleep easier now that I looked that one up. |
point well made, although
a) Testing for CE approval is assumed but not proven
b) the same document also says:
"whereas such equipment should be permitted to be put into service for its intended purpose; whereas the putting into service may be subject to authorisations on the use of the radio spectrum and the provision of the service concerned;" :-) |
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carl_w
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Joined: Mar 13, 2004
Posts: 242
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| Posted: Fri Jul 14, 2006 11:22 am Post subject: |
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| Eldar wrote: | | OK, you win - I was wrong all along, you can't change the bloody legislation in this fascist state, you can only prove that it is applied incorrectly. |
Now on that we're in complete agreement. :D |
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