Re: [Amps] OT: RF Speech Processor Kits - Final Final

[Gary Schafer <garyschafer@comcast.net>]

Steve Thompson wrote:
> On Monday 17 January 2005 01:02, Gary Schafer wrote:
>
>
> > Hi Steve,
> >
> > The output of an ssb transmitter is different than from a double side
> > band transmitter. A double sideband transmitter produces a replica of
> > the input wave form. An ssb transmitter does not.
> >
> > A double side band transmitter modulated with a sin wave will produce an
> > envelope with a replica of that sin wave.
> >
> > An ssb transmitter modulated with a sin wave will only produce an rf
> > carrier out. No replica of the modulation signal.
> >
> > A square wave fed to a double side band transmitter produces a square
> > wave out.
> >
> > A square wave fed to an ssb transmitter produces only an infinite spike
> > in amplitude out, not a square wave.
>
> There's always something for me to learn from Pappenfus, Breune & Schoenike. 
> The infinite spike requires infinite bandwidth - in practice the highest 
> harmonic is likely to be 9th (2700 from 300 x 9) so the peak isn't infinite, 
> but under 3x average.
>
>
> > That is the problem with audio clipping for an ssb transmitter.
> >
> > Clipping at rf produces the same replica of the output as that of the
> > input to the rf clipper.
> >
> > Split band audio clippers are better than base band clippers but you
> > still can not filter out all the harmonics generated by clipping.
>
>
> Why not? For example, frequencies from 300Hz to 500Hz are filtered and 
> clipped. The harmonics fall in the range 600Hz upwards. The clipped signal is 
> passed through a filter that passes 300-500Hz and chops everything from 600Hz 
> and upwards - there are limits as to how close to infinite you can make the 
> attenuation, but it's practical to reduce the harmonics at the output to an 
> insignificant level. Clipping a 300Hz sine wave in this way doesn't produce a 
> 300Hz square wave at the output - and so on for any frequency.
>
> 73, Steve


It does not have to be an infinite bandwidth to cause problems. The 
point is that any time you clip the audio signal it gets somewhat 
squared off. Sending that somewhat squared off audio into the 
transmitter causes the transmitter to transmit a higher amplitude sharp 
spike compared to what it would if the audio was in sin wave form.
This raises the peak envelope power higher than the average, just the 
opposite of what you are trying to accomplish.

What comes out of an ssb transmitter is not a replica of what goes in.
Speech processing that works well on AM does not work the same on SSB.

73
Gary K4FMX


_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps