[AMRadio] Monitoring Modulation


Bry Carling bcarling at cfl.rr.com
Fri Nov 15 15:03:43 EST 2013


Thanks Don. 



Bry Carling
http://af4k.com

> On Nov 15, 2013, at 1:48 PM, "Donald Chester" <k4kyv at charter.net> wrote:
> 
> From: W2XJ <w2xj at w2xj.net>
> 
>>> ... I always trust a scope before a mod monitor. Properly clipped negative
> peaks are easy to see and the absolute value of positives are not important.
> In broadcast it is common practice to modulate as much positives as the TX
> can take and in amateur operation a peak power measurement is the only thing
> that really counts. >>
> 
> I don't fully agree. 
> 
> In broadcasting, the positive peaks are limited to 125% positive by FCC
> rules, and FCC inspectors are extremely picky with broadcasters. There is no
> such limitation in amateur operation. If there were, then SSB would be
> illegal, since there is no carrier at all and therefore ANY modulation would
> be "in excess of 125%".
> 
> With AM, you NEVER want to reduce modulation percentage to limit "peak
> power"; the total sideband power of a full-carrier AM signal is low enough
> as it is.  What  "really counts" is whether or not the positive peaks are
> flat-topping as a result of exceeding the modulation capability of the
> transmitter. Flat-topped positive peaks generate precisely the same kind of
> splatter and distortion as does overmodulation in the negative direction.
> Modulate as much as you can without  exceeding 100% in  the negative
> direction OR seeing flat-topping on positive peaks.  I always try to have
> enough modulation capability built into the transmitter to allow me to
> modulate to just shy of 100% negative, and then let the positive peaks go
> where they may with the natural waveform of my voice, without any danger of
> flat-topping. If you are that concerned about what the power level hits on
> an occasional voice peak, then for God's sake, reduce the carrier level and
> make sure you are still fully modulating what carrier you have; don't run a
> hefty carrier that is less than fully modulated as described above.
> 
> Don k4kyv
> 
> 
> ---
> This email is free from viruses and malware because avast! Antivirus protection is active.
> http://www.avast.com
> 
> ______________________________________________________________
> Our Main Website: http://www.amfone.net
> AMRadio mailing list
> Archives: http://mailman.qth.net/pipermail/amradio/
> 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


More information about the AMRadio mailing list

This page last updated 21 Nov 2017.