[Amps] Audio BW -- Please just let us operate!!

[Vic Rosenthal]

Paul Christensen wrote:

>  http://www.aorusa.com/ard9800.html
> 
> With a bit of data augmentation, such a product has real promise for those
> wanting to explore high fidelity audio on the HF bands.  The modulation
> technique in this unit is DPQSK.
> 
> Since this is an AMPS mail group after all, I am interested in knowing more
> about the peak-to-average ratio of the data and how it fits within the
> acceptable duty-cycle of today's commercially-manufactured amplifiers.

I just looked at the web site, and since this device uses a form of PSK 
modulation, I get the impression that the duty cycle is 100%.  So you 
would use RTTY ratings.

It's important to distinguish between the method of ENCODING a digital 
signal (which is what I was talking about) and the method of MODULATING 
an RF signal to transmit the digital information.  The encoding sets the 
minimum theoretical bandwidth that is required to transmit a given signal.

Modulation is the process of converting the bits in the digital stream 
to RF that varies in some way, so that a receiver can recover the 
original digital stream which it will then convert to audio.  Various 
modulation methods will be able to approach the theoretical minimum 
bandwidth more or less closely.  Other things that depend on the 
modulation scheme are the ability to recover signal in the presence of 
interference, and duty cycle.

Normal AM and SSB are ways of modulating RF directly from an audio 
signal.  Adding a digital encoding step (and corresponding decoding in 
the rx) allows us to use what we know about voice signals and how they 
are perceived by the brain to selectively remove information from the 
signal to reduce bandwidth without damaging (perceived) fidelity.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco