[AMRadio] Frequency Response

Gary Blau gblau at w3am.com
Sat Sep 25 00:20:56 EDT 2004

IMHO, the best approach is to terminate the mod xfmr (or any audio xfmr)
for best transient (square ware) response of the modulated envelope, not
just an arbitrary upper frequency.
Adjust for best stability, least overshoot and ringing on leading edges,
and the least tilt.  Check it at mid freq's, say 1khz, as well as low
(50hz) and high (5khz).  It's easier to see the tilt on the low end, and
the overshoot on the midrange.  All of these disturbances rob modulation
power from you, as you have to reduce average modulation level to keep
the peaks from overmodulating.
Cleaning it up will help maximize modulation control, sometimes as much
as several db.  This in turn increases potential average loudness which
is the name of the game.  

The best place for audio bandwidth control/limitation is in the low
level audio chain.
As to where to roll it off, I'd suggest 5khz, but I like to make it
variable depending on conditions.
With only 3KHz you might as well be on SSB.


Edward B Richards wrote:
> Tom;
> I believe the standard for communications is 300 to 3000 CPS +/- 3 dB.
> On Fri, 24 Sep 2004 14:54:49 -0800 "Tom Elmore" <tom at telmore.com> writes:
> > I am in the process of restoring a Stancor 60-P transmitter to
> > service. I
> > have replaced all the capacitors in the power supply and in the
> > audio
> > amplifier sections.  I would like to terminate the modulation
> > transformer
> > with the correct resistance and check for frequency response on my
> > scope.
> > What is a good ballpark response that I should use for operating AM
> > in the
> > amateur bands.
> >
> > Thank You
> > Tom Elmore KA1NVZ
> > Anchorage  Alaska

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