ComReg gives green light to i-Trips

watty

# Permitted Short Range Devices in Ireland
http://www.comreg.ie/whats_new/default.asp?ctype=5&nid=102529


# ComReg gives green light to i-Trips
http://www.comreg.ie/whats_new/default.asp?ctype=5&nid=102530

mwrf

I dont like how it states "i-trips".
It should state fm transmitters so as not to confuse the consumer into thinking that only i-trips are permitted.

Ulsterman 1690

"FM transmitters" could confuse the public too into thinking that pirate radio was now legal ?

mwrf

something like "extremely low powered fm transmitters" then

watty

From Comreg:
The FM radio band is 87.5 - 108 MHz and is the primary frequency band in Ireland for
audio broadcasting.
Interface requirements are the technical and administrative conditions in place for the use
of the radio services e.g. frequency bands, power levels and licensing regime.

They don't call it an iTrip in the regulations:
http://www.comreg.ie/_fileupload/publications/odtr0271R.pdf

In fact scroll to right and see they don't give it a name at all!

[B]Table 11: Interface Requirements for Wireless Audio Applications[/B]
Frequency Band 		Maximum 
			Permitted Radiated
			Power/Field Strength	Reference Standards 		Relevant Documents/Other notes
---------------------|-----------------------|-----------------------------|--------------------------------------------
31.025 – 31.325 MHz 	10 mW ERP 		Ref to TTE 9 			Analogue cordless phones only
						(see document odtr98/62R)	Legal references: S.I. 405 of 2002, S.I.
										160 of 2006
										Other references: ERC/REC 70-03
---------------------|-----------------------|-----------------------------|--------------------------------------------
39.925 – 40.225 MHz* 	10 mW ERP		Ref to TTE 9			Analogue cordless phones only
						(see document odtr98/62R)	Legal references: S.I. 405 of 2002, S.I.
										160 of 2006
										Other references: ERC/REC 70-03
---------------------|-----------------------|-----------------------------|--------------------------------------------
49.82 – 49.98 MHz* 	10 mW ERP		EN 300 220			Baby Monitors
										Legal references: S.I. 405 of 2002, S.I.
										160 of 2006
										Other references: ERC/REC 70-03
---------------------|-----------------------|-----------------------------|--------------------------------------------
87.5 – 108 MHz 		50 nW ERP  		EN 301 357
Channel Spacing: 200 kHz							Legal references: S.I. 405 of 2002, S.I.
										160 of 2006
										Other references: ERC/REC 70-03

Ulsterman 1690

Odd that theyve adopted a 200 KHz frequency spacing (USA standard) for these devices.

Does that mean that 100 KHz step devices are still illegal (even if CE marked ?)

And isint the 50mW output limit rather low given that leakage from the local oscillators of many FM recievers can (in ERP terms) be as high as tens of microwatts ?

Indeed the first transmitter I ever built was nothing more than an FM reciever modified by feeding audio via a small decouplng capacitor into the AFC circuit for modulation with the output of the local oscillator tapped off into a long wire aerial.

It covered three streets

watty

I guess they think 50nW is enough to get from the dashboard to the car aerial, and they don't want it covering 3 streets.

Though some people play car stereo so loud I can hear it 1/2 a street away with the windows closed on both cars.


I'd suggest the 200kHz is the maximum channel bandwidth of transmission, not the tuning step.

Ulsterman 1690

I'd suggest the 200kHz is the maximum channel bandwidth of transmission, not the tuning step.

Possibly although unless they incorporate some sort of deviation limiter and dont use stereo Id say most of them will have a bandwidth of 300 KHz or more !

The COMREG bandwidth spec for a licenced FM broadcast station with stereo RDS and full deviation is 270 KHz

Though some people play car stereo so loud I can hear it 1/2 a street away with the windows closed on both cars.

In most cases the stereo probably cost more than the car did :rolleyes:

watty

For those interested in Tech details (I'm sure UM1690 knows most or all of this)

Minimum for stereo at M=1 is (38kHz + 16KHz) x 2 which is less than 115kHz. 200KHz is just under M=2. Do any iTrip thingys do RDS? I'm told most really are stereo MPX encoded (19kHz pilot + 38kHz DSBSC L-R)

Offical Stereo FM used to be 250kHz, Reducing M below 2 has effect of reducing S/N. So for example M=1 (Narrow Band FM) has poorer S/N performance than DSBSC AM of same power.

I'd have put limit at 250KHz.

Too wide and you get distortion on both high frequency and louder sounds as you exceed the typical ceramic filter bandwidth of 250kHz. To an extent the deviation is dependent on your mp3 player volume.

I suggest the user turns dowm main volume and increases MP3 till they just detect distortion and then back off a bit. Then not that setting. Use then Main Radio volume and you have best compromise between S/N and Distortion.

It won't be much off 200kHz peak by that method. Assuming sensible encoding of MP3 and not the quality of voice mail.

*DSBSC can be done with a single doubly balanced modulator, easily a standard cell of an IC. It is like AM with carrier removed afterward.
*M = modulation index. 1 is roughly phase modulation or NBFM, and bandwidth is always twice audio bandwidth for pure phase Modulation.

lawhec

They've been legal up here in the north since Ofcom legalised them at the start of the month.

At the moment the NCFM network is as follows...

NC's bedroom (main transmitter): 104.8
NC's sitting room (relay): 103.9
NC's sunroom (relay): 104.3
NC's garden shed (relay): 105.2
NC's kitchen (relay) is off-air at the moment due to a tea spillage, but will return on 106.1

Antenna

interesting reading here:
from
http://www.ebu.ch/CMSimages/en/tec_text_r120-2007_tcm6-49264.pdf

"4. Low-power FM modulators should have a full band tuning range (87.5 – 108 MHz) in order to
prevent a concentration of the interference in some frequencies.
"

this is a problem with most of the non-Itrip ones, like 'Tune-Free' which are for sale here. These ones only have a few selectable channels (not any of the clearest!) , none of which might be suitable in some parts of the country.

Ulsterman 1690

NC I thought as bad with my four transmitters (one on desktop PC one on satellite box one on Ipod in Car and one spare) and I never even thought of networking them

Watty I thought the commonly accepted formula for FM bandwidth was Carsons Rule i.e.

(2 times peak deviation) + (2 times highest modulatng frequency)
Which for FM stereo with no RDS and standard 75 KHz deviation

( 2 times 75) + (2 times (38 + 15) ) =
(2 * 75) + (2 * 53) =
(150) + (106) =
256 KHz

Mono would be 180KHz (75 KHz deviation) or 130KHz (50 KHz deviation)

And most one can overmodulate/overdeviate to a considrable degree before distortion becomes evident on most consumer FM radios

Some interesting quotes on this topic in the link posted by Antenna

The frequency modulation of the transmitter output of these devices should be limited to a deviation of ±75 kHz, as applied to regular FM broadcast signals. Thus the devices must be equipped with an appropriate limiter......Another type of interference can occur with low-power FM modulators as a result of excessive deviation of the frequency modulation in these devices. Deviations up to 243 kHz (instead of the 75 kHz maximum deviation normally used in broadcast transmissions) were measured in some devices. Spectrum occupation of up to 800 kHz was also measured,

:eek:

Sponge Bob

Deviation ???

I'll give them Deviation

lawhec

NC I thought as bad with my four transmitters (one on desktop PC one on satellite box one on Ipod in Car and one spare) and I never even thought of networking them

Ah come on Ulsterman, you didn't think I was serious? Didn't notice the little wink smiley just below the "network"?

Mind you, it'll probably be bought out by the Northern Media Group within the next 12 months!:D

Ulsterman 1690

Mind you, it'll probably be bought out by the Northern Media Group within the next 12 months!

ROTFL

But seriously NC let us know when you make it onto DAB

zilog_jones

What kind of range is a 50nW transmitter expected to do? I have some cheap-ass transmitter (this) and can get a good 30-40 metres before it's completely drowned out by Newstalk

I can't find any spec's for that particular transmitter, but some eBay description claims the range is "up to 10m (approx)".

lawhec

zilog_jones wrote:

What kind of range is a 50nW transmitter expected to do? I have some cheap-ass transmitter (this) and can get a good 30-40 metres before it's completely drowned out by Newstalk

I can't find any spec's for that particular transmitter, but some eBay description claims the range is "up to 10m (approx)".

I have one of them, I suspect their power is a bit more than 50nW - possibly around 10-100uW. As long as you don't abuse it I can't see them being a problem.