WWWR wrote:
>Bob,
>
>
>
>I still have trouble understanding how the content delivery mechanism --
>whether it be satellite, T1, or a less sophisticated telco type service --
>could produce fluctuations in the carrier frequency.
>
>
>
>
Curt,
Here goes an attempt an an explanation:
T-1 bundle of frequencies are downlinked along with the beacon signal.
Signal frequency and local oscillator signal in effect downlinked
together. Demuxer locks on to beacon signal (which is, I think, just a
carrier) and resultant inside demuxer is a group of frequencies which
could be inside MW BCB except they are confined to the demuxer. I think
there's a tap point brought out at back of demuxer and you could
actually connect a BCB receiver to tap point and tune through T-1 spectrum.
I think.
>As I mentioned, it seems to me that for a wobbling heterodyne to be created
>by beating a local oscillator against the received signal, the variations
>would have to be in the carrier, not in the modulation. I'm probably missing
>something very simple, or something beyond my pay grade.
>
>
>
I think you're right so far. Anyway, at the output of the demuxer which
(I think) again can be a spectrum inside MW BCB but which typically
extends way beyond either way, you have the spectrum. The spectrum is
further decoded/demodulated by a T-1 receiver that "sees" the downverted
spectrum and then further breaks it down to audio or computer-type data
package or most anything.
I think.
Data package goes to server, or something. Also, I think that when any
T-1 subchannels is inactive, it is cut off at the uplink station. The
frequencies carried by a satellite are a complex mixture of all kinds of
T-1 carriers. Any single carrier comes out of the total budget for the
download transmitter. Remember, that satellite is up there and depends
on solar cells and whatnot to power it up. Spectrum and power are precious.
When any carrier in the T-1 spectrum goes down (for the outlined
economic purposes), that channel on the final demodulator, its AGC rises
(or falls) and the inactive channel can then let through all kinds of
junk generated inside the final demodulator.
I think.
That channel goes to the BCB transmitter as AF modulation. But some MW
frequency junk can get through to the transmitter and get put on the air.
I think.
I've been through three/four classes on specific demux receivers.
Modems. Learned the receiver well enough to be dangerous. Now, almost 2
years later it all is starting to fade out on my mental facilities. My
AGC rises (falls) and junk starts coming through. And I foist it off on
you as the output of someone who knows but really just knows just enough
to make myself a real dangerous individual.
Feedback?
Charles
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Charles A & Leonor L Taylor
Greenville, North Carolina