🚀 go-pugleaf

In article <XNWLi.896$ht5.398@trnddc02>,
 "Earl Kiosterud" <someone@nowhere.com> wrote:

> "SFTV_troy" <SFTV_troy@yahoo.com> wrote in message 
> news:1191140172.205755.136880@y42g2000hsy.googlegroups.com...
> >
> > Earl Kiosterud wrote:
> >>
> >> Synchronous AM demodulation uses a locally regenerated carrier, 
> >> fed along with the AM signal (upper or lower set of sidebands) to 
> >> a multiplier (modulator).  The result is the audio. It replaces 
> >> the envelope (diode) detector usually used. You can think of it as 
> >> another superhet stage where the result, instead of another IF 
> >> frequency, is the baseband audio.  That's because the local 
> >> oscillator is the same frequency as the carrier of the (IF) 
> >> signal, so the difference is zero.  The sidebands wind up 
> >> translated to baseband audio instead of to another IF frequency.
> >>
> >> There are advantages.  Since one set of sidebands or the other can 
> >> be used, if there's a distant station 10KHz away, causing that AM 
> >> whistle, you just switch to the other set of sidebands, whichever 
> >> comes in the cleanest.  Also, it doesn't depend on proper 
> >> amplitude and phase of both sets of sidebands to work properly, as 
> >> does the regular envelope detector, so it works better with 
> >> impaired signals.
> >
> >
> >
> > I only understood about 75% of what your wrote, but if I understand 
> > your meaning, this new receiving technique would not improve the 
> > sound (it would still be limited from 100-6000 hertz), but would 
> > only reduce interference.
> 
> 
> Troy,
> 
> Well, the 6 KHz limit is due to the narrow bandwidth of the 
> receivers, not the detector used, or the stations.  I think most AM 
> radios actually do much worse than that.  AM radios are designed with 
> a limited bandpass because it gets noisy as the bandwidth goes up.  
> The AM band is a soup of distant stations, particularly at night, and 
> that's the source of much of the noise.  AM radio stations in the US 
> are allowed up to 10 KHz audio.  That's pretty listenable -- there's 
> only a little over a half octave to the 15 KHz limit of FM.
> 
> The synchronous detector, in addition to being able to use one set of 
> sidebands or the other, whichever is the best under the conditions, 
> is not subject to distortion from asymmetrical sidebands, such as 
> when there is fading, multipath, etc.  There may be a non-flat audio 
> bandpass from those conditions, but a conventional detector will also 
> have distortion.

I just made a few empirical measurements on a receiver with digitally 
adjustable filters and noted increased high end audio response out to 
8K. 8 khz wide is not pleasing because most radio stations are 
apparently boosting the high end. I usually set the bandwidth 4.4 khz 
for best sound otherwise it is to sharp.

-- 
Telamon
Ventura, California