[AMRadio] Negative Loading circuits - good, bad, or ?


Jim Candela jcandela at prodigy.net
Tue Jan 10 09:38:35 EST 2006


Todd,

   There are various reasons for using "Negative
Loading circuits". If you are ineterested in
maintining a high average modulation percentage
without splattering from negative cycle over
modulation, then may I suggest a few first steps:

1.) get your speech polarity correct since your voice
on a scope is probablly asymetrical.

2.) Use some form of peak limiting (not hard clipping)
in the audio chain.

3.) Use a scope while modulating to keep track of
where you are. I like X;Y or Trapezoid mode for this.

   As far as modifying your transmitter to achieve the
same end, lots do it, some sound like hell, and others
work out pretty well. I prefer the approach that is
transparent until a certain - modulation percentage is
achieved, say 85% negative. At that point a
combination of a bias supply, diodes, and resistors
kick in to either load, or attenuate the negative
cycle from that point on. The circuits that load the
negative cycle all the time are the ones that in my
opion sound like hell, and need to be avoided. I have
used on a couple of rigs a circuit that I call PNCL,
"progressive negative cycle loading", but that is
another story.

As for protecting your iron, a spark gap on the
primary plate to plate might be better than one across
the modulation transformer secondary...opinions?

Regards,
Jim 
WD5JKO



--- "Todd, KA1KAQ" <ka1kaq at gmail.com> wrote:

> Just curious to get some opinions on these circuits,
> the best design
> to use, or if I should use one at all.
> 
> Brett, I heard talking about the negative loading
> cycle circuit
> causing problems for you, I wonder if you could
> explain more? It's
> something I had thought about adding and have talked
> with folks who
> swear by them. Is there are good way and bad way to
> do so, or is it
> just a bad idea from the start? The initial reason
> that interested me
> was protection of the mod iron.
> 
> ~ Todd/'Boomer'  KA1KAQ
>
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