[AMRadio] Only function of carrier

[Gary Schafer]

Actually the low frequency response wastes a lot of power for
communications. There is not much intelligence in the low frequencies
compared to the mid frequencies. With flat audio response the low
frequencies tend to take up a large chunk of the modulation percentage. This
limits the modulation power in the mid range where most of the intelligence
is. 
This is very evident when running the audio into a simple clipping circuit.
That is one of the reasons that low frequencies are rolled off on voice
communications circuits. It allows a higher percentage of modulation of the
mid frequencies where it matters.

Motorola, Collins and many others figured this out a long time ago.
That type of audio does not sound as pleasant as full spectrum audio but it
is more effective for communication.

Don, K4KYP has stated many times that he rolls off his highs and lows so
that the audio sounds balanced and it limits the bandwidth while still
providing nice audio and no growling lows which would be present if just the
highs were rolled off.

Now if you run a lot of sophisticated audio processing then much can be done
to make the signal sound louder.

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of Stevan A. White
> Sent: Monday, April 25, 2011 4:00 PM
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] Only function of carrier
> 
> I'll add this observation to the comments below; some folks have what I
> call "Motorola disease."  They cut off a lot of bass (low freq) response
> which may be OK for an FM repeater but it is the LF response that gives
> the real power to the audio so they're really shooting themselves in the
> foot.  You don't need the bass response growling but don't kill it
> completely either.  I'd pass LF down to at least 100 Hz (lower if you
> like) but keep the upper end up to at least 7.5 kHz; you'll sound a lot
> better, and more natural too.  As a broadcast engineer I am accustomed
> to going up to 125-135% modulation on positive peaks and limiting
> negative peaks to about 95%.  It doesn't add an appreciable amount of
> distortion, it's easy to hear and understand, and it cuts through the
> crud fairly well.  Of course, there's nothing like having everything
> from the mic to the antenna optimized.  It makes a world of difference
> on the receiving end and is easier on your equipment too.
> 
> 73 de W5SAW, Steve White
> > The only function of carrier is to operate the detector circuit.  The
> time constant is long on the  output of the detector at the IF freq, the
> carrier converted down to the IF freq. charges this RC circuit up.  As
> the upper sideband signal, being a higher freq,  adds to the output of
> the detector as its higher IF freq.  switches the circuit on and off
> generating more charge, the LSB signal subtracts from this voltage as
> it's lower freq allows the circuit to discharge.  The output is a
> waveform that represents the transmitted audio and is sent to the audio
> amp.  100% modulation on  any RF carrier level is the best you can get
> for fidelity, but maybe not communication punch through ability.
> >
> > Now, for the folks that think base response is the be all end all for
> AM,  weak signals are impossible to copy when you are all base, no
> highs.  There are a lot of signals I hear with my R390A, Hammer 170A and
> R4C that could be copyable if only they had full range of audio, but for
> some reason, their owners bow to the god of low freq range audio.
> >
> > Charlie, W4MEC in NC
> ______________________________________________________________
> Our Main Website: http://www.amfone.net
> AMRadio mailing list
> Searchable Archives: http://www.mail-
> archive.com/amradio at mailman.qth.net/
> List Rules (must read!): http://w5ami.net/amradiofaq.html
> List Home: http://mailman.qth.net/mailman/listinfo/amradio
> Post: AMRadio at mailman.qth.net
> To unsubscribe, send an email to amradio-request at mailman.qth.net with
> the word unsubscribe in the message body.
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html