Re: Radio Questions

[jdouglas@mitre.org (jason douglas)]

>. But what is the ARI-Z button? It does not seem to have
>     any effect on the increased sensitivity for cowboy music... but
>     seriously, what does this button do?  Thanks

Nothing in the US of A.  That is to say, ARI is a well-used service in
Germany that never caught on here.  Insufficient commercial incentives, I
guess.  (In Germany, the radio stations are all public).

ARI is an FM  sub-carrier based program broadcast in Germany (and maybe
other european countries too?) used for traffic reports.  The programs are
broadcast periodically.  Of course there are special bulletins too.  My old
('82) 100 had an ARI equipped factory radio, and you could set it so that,
even with the volume all the way down, the volume would come up just for ARI
messages.  You could also switch from regular programming or even from a
cassette tape!  Too bad we don't have 
that here - you have to endure the morning drive time programs (unless you
listen to NPR :-) ).  The ARI broadcasts only discussed the autobahnen,
though, not the secondary and local roads.

For the curious with little background in radios, a subcarrier is a  carrier
signal modulated onto the carrier. Put another way, the, say 100 mhz carrier
(sine wave) signal is modulated with a, oh, say, 100 khz wide signal.  This
100 khz wide signal includes a baseband audio signal and one or more low
frequency carrier (sine waves).  These low frequency carriers are called
"sub-carriers," and they can be modulated to carrier data, voice, etc. The
classic example is stereo  FM.  The signal modulated onto the carrier
includes a baseband  signal that  is actually the right + left channels
summed together. It also includes a subcarrier at (I think) 38 khz) that  is
modulated with a difference signal (i.e., r - l, or is it l - r?) used to
derive the separate right and left channels.  Once the main (i.e., 100 +/-
mhz) carrier is demodulated, the sum signal and the subcarrier are
separately filtered out to different parts of the stereo demodulator.  The
subcarrier is demodulated to yield the difference signal.  The difference
signal is added to the sum signal for one channel, and subtracted (inverted
and added) to the sum signal for the other channel.  The presence of the
subcarrier is used to light the "stereo" light on your radio.  Sometimes,
other subcarriers are used for pay-per-use signals, such as muzak used in
stores, etc.  This technique is also, I think (I've been out of school for a
while, guys!) used for modulating the sound onto the t.v. signal carrier.
------------------------------------------------------
Jason Douglas
MTS Dept G057                        
MITRE Corporation