[BC] Noise free radio...

[Burt I. Weiner]

It seems to me that at the receive end you would not only be 
multiplying the intended information, but all of the phase shift and 
anomalies that happen in propagation along the way.  I never had the 
good fortune to see a demonstration of it.

Burt


At 12:09 PM 10/6/2007, you wrote:
>From: "Harold Hallikainen" <harold at hallikainen.com>
>Subject: Re: [BC] Noise Free Radio
>To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
>Message-ID:
>         <58551.192.168.1.1.1191694287.squirrel at sujan.hallikainen.org>
>Content-Type: text/plain;charset=iso-8859-1
>
>
> > On Saturday 06 October 2007 12:52 pm, Dale Adkins-WINI wrote:
> >>  I've forgotten the details, but twenty or twenty-five years ago
> >>  George Yazell was promoting a project he called "Noise Free Radio"
> >>  in which you would frequency modulate  your AM carrier.
> >>  Can somebody relate what ever happened to the proposal?
> >
> >  For some reason, it died on the vine.
> >  ( too early, I suspect )
> >
> >  'Twas a simple concept.
> >  FM the AM carrier some miniscule deviation.
> >  Transmitting is easy.
> >
> >  At the receiver, multiply the AM carrier up by some large
> >  factor, such that the deviation was now about 75 khz, then mix
> >  that to produce an IF of 10.7 Mhz, and feed it into the normal
> >  FM if strip.
> >  Receiving, not so easy.
> >
> >  Then, the whole idea has some challenges.
> >  What happens when the modulating frequency exceeds the deviation ?
> >  Part of the concept involved modulating FM an AM carrier with 15 Khz
> >  audio, but deviation of the carrier was something like 5 hz.
> >
> >  To this day, methinks it could be done, but the technology for detecting
> >  the instantaneous rate of change of the rate of change of the
> > instantaneous
> >  carrier phase just didn't exist with any reliability to function in the
> > real world.
> >
>
>I don't think the multiplying and hetrodyning gets you and andvantage over
>just doing FM demodulation at carrier or some IF. I tend to think of
>bandwidth and snr as two forms of the same thing, just as energy and
>matter could be thought of as two forms of the same thing. You can trade
>one for the other, but the sum is the same. If you have a digital channel
>that can handle a certain bit rate, you can either run a wide frequency
>response audio signal (high sample rate) or a high snr audio signal (more
>bits per sample). In RF, you have a channel of a certain width, and you
>have a snr for the channel. These two determine how much information you
>can shove down the channel. In FM, we get a better demodulated snr because
>we are running a wider channel. In the proposed noise free radio, the
>channel was not wider, so there would be no demodulated audio snr
>advantage. In addition, the narrow deviation required to stay within the
>channel made the sideband power pretty low, making the effects of channel
>noise worse than on AM.
>
>I recall a station in Florida got an experimental authorization for the
>proposed narrow band FM. I never saw the report, though.
>
>Harold

Burt I. Weiner Associates
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