BTW, Bill, amplitude modulation and "mixing" are the same process
mathematically. In a "mixer" we just select one of the "sidebands"
-depending on whether we are doing "up-conversion" or "down-conversion"
mixing. So, in an optical fiber, passing 2 MHz 160m RF, there would be two
sidebands at 2 MHz above and below the optical carrier frequency. The
photo-diode would see the optical carrier and the +/-
2 MHz sidebands as an amptltude modulate optical carrier and we would select
the lower sideband to recover the 2 MHz "baseband" signal.
73,
Charlie, K4OTV
73.
Charlie Cunningham
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Bill
Wichers
Sent: Thursday, October 24, 2013 1:39 PM
To: Tom W8JI; Shoppa, Tim; Bruce; topband@contesting.com
Subject: Re: Topband: Light fiber question
I see your point, since the signal is undergoing a conversion. My thinking
was modulator = baseband to some kind of RF or digital signal, i.e.
something very different from the original signal in terms of content of the
waveform. I wasn't thinking of using a band-limited section of spectrum
being converted to an amplitude-modulated light source as a "modulator" in
this case.
What I had meant was that the electrical->optical conversion doesn't have to
be a particularly fancy system when you're only trying to run about 200kHz
of spectrum over the fiber in the 2(ish)MHz range. The basics I mentioned
before and some op amps are all that are needed. The op amps will likely be
the limiting factor for dynamic range.
I do agree with you that a simple run of decent coax is likely to be the
better option though.
-Bill
> Sorry, but by definition that is a modulator and demodulator.
>
> You have to convert the radio signal to light, and that involves
modulating
> a light beam of some type. At the other end, you have to demodulate the
> light into the original baseband.
>
> You may not recognize it as a modulator/demodulator system, but that's
> what
> it is. You cannot just hook the coax to the fiber optic cable at each end.
>
> 73 Tom
_________________
Topband Reflector
_________________
Topband Reflector
|