[BC] Re: FM Band and other uses for 19 kHz

[Xmitters@aol.com]

In a message dated 1/18/06 10:39:06 AM Central Standard Time, 
broadcast-request at radiolists.net writes:

<< Ok  Brain trust  I have several questions.    What  can we technically use 
 10% of the FM signal at 19 kHz.  for other than  light the stereo light (not 
 primary) and phase locking the 38 kHz. DSSB  suppressed carrier?>>

I would doubt that there is little else we can do with it. I think legacy FM 
stereo receivers would gag due to the modulation of the pilot with a secondary 
service.
  
 <>

Frequency shift keying also means phase modulation. Your L-R channel would 
likely be decoded full of cross talk from the secondary service, modulating the 
pilot tone.
  
<< I have heard discussion of amplititude modulating the 19 kHz. low response 
 
 with no cut off below 2% modulation for telemetry tones.>>
  
 <<Since it was such a small amount of bandwidth and % of  modulation.   
Think 
 about it.   It seems that we are wasting  10% modulation when the receivers 
 could be locked with todays  technology.   >>

I suppose you could look at it that way :-) I think 10% is worth it, because 
by reducing it, you reduce your FM stereo coverage. So I feel I am getting my 
money's worth out of the 10% :-)
  
 <>

If there is a way to modulate 19 kHz without screwing up its primary 
function, that would be great. Given that it's crammed in there between 15 kHz and the 
lower end of the stereophonic subchannel, we don't have much bandwidth to 
play with.
  
<< Think out of the box.......Comments and ideas???>>

First thing I would do is to come up with a modulator to modulate the 19 kHz 
pilot in the various modulation types, then increase the modulation of my 
proposed secondary service and look at the recovered stereo. My initial hypothesis 
is, I doubt we would get away with much before problems would surface. I 
would be very concerned about how insensitive other receivers would be to this 
added modulation service. My lab receiver might be OK with it, but what about the 
wide variety of receiver quality out there and what kinds of problems would 
pop up? Then it becomes a matter of what types of service could we transmit in 
that discovered bandwidth. It would be interesting to experiment and see what 
we could get by with. I would not however, hold my breath and/or quit my day 
job in anticipation of becoming filthy rich :-)

You could probably do _something_,but would that something have enough 
useable bandwidth with which to do anything productive? If I had to guess, I would 
guess no. 
  
 Dave >>

Jeff Glass, BSEE CSRE
Chief Engineer
WNIU WNIJ
Northern Illinois University