On 8/2/2014 6:12 AM, Jeff wrote:
On 02/08/2014 00:13, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrgvk8$5er$1@dont-
email.me:

I won't get into the math here, but due to the sidebands (yes, FM has
sidebands, also - the number and strength of the sidebands is
proportional to the deviation and modulating frequency), frequency
response of the modulated signal is proportional to the bandwidth of the
channel and deviation. A 5 kHz deviation can theoretically pass up to
about 5Khz of audio, but in practice it's limited to about 3 kHz (to
avoid adjacent channel interference). This is fine for voice, but does
not work well for music (try listening to music on the AM band, for
instance).


Thankyou, that's great help. I'll have to be careful about buying one of
those widgets... I did suspect that something that had a narrower
bandwidth
would reduce frequency response (based on playing with the AR-3000 on
narrowband FM). That's one reason I was wondering about boosting the
broadcast signal directly for low level rebroadcast in a building, to
keep
what fidelity I can as best possible.


The point that Jerry is missing is that the in-car devices that link an
MP3 player, and the like, to a car radio are being received by just
that, a car radio; so if the deviation were as low as 5 or even 15kHz
then the level of audio coming out of the radio would so so low as to be
unusable.


Wrong. These are operating in the commercial FM band, and use 75 kHz
deviation. I never said otherwise.

The deviation of the transmitters must match the bandwidth of the
receiver being used, ie the normal FM broadcast band deviation of 150kHz
of more.


Again, incorrect. The deviation is 75 kHz (deviation is measured from
the center frequency). Bandwidth is 150 kHz.

I am not sure what the FCC power limit for such devices is, but in the
UK is it is 50nW erp in the FM broadcast band, yes 50 nanowatts. I
expect that the devices sold in the US are similar output power.


Again, incorrect.

Jerry does not seem to take on board that this is an international
group, not a group of ex-US cable technicians who slovenly misuse dBm to
mean dBmV, when the rest of the world uses dBm correctly to mean dB
relative to a milliwatt.

Jeff

Nope. I'm talking about what is commonly used here. But there are some
people from the U.K. who think they are experts on everything.

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