[AMRadio] 7285Kc tomorrow/Saturday


Jim Candela jcandela at prodigy.net
Mon Jan 9 11:32:16 EST 2006


One way around the sync problem is to use the
Trapezoid pattern by using scope in X:Y mode. That
gives you different information but seeing > 100% + or
- is easy to see, as is any non-linearity in the RF
plate modulated amplifier. Of course if you have audio
to the scope, and it's a dual trace scope, then you
can stay on the RF envelope pattern, and trigger on
the audio channel. You may need to adjust the trigger
settings, and the sweep rate so that a "yea yea" into
the Mic will always trigger and show a stable
triggered pattern. I do both Trapezoid and envelope
here.

--- "John E. Coleman (ARS WA5BXO)"
<wa5bxo2005 at pctechref.com> wrote:

> I think what Mark is saying is that it it's
> difficult to tell what
> percentage modulation you're at when the wave form
> is not a sine wave and is
> not synced and this is true. You just have to get as
> close as you can with
> out pinching the carrier (not too often anyway).  An
> automatic gain control
> circuit helps a lot with this.  I did with out one
> for years learning how to
> talk by watching the scope.  But it is a lot nicer
> and more relaxed when you
> have one.
> 
> John
> 
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net
> [mailto:amradio-bounces at mailman.qth.net] On Behalf
> Of W5OMR/Geoff
> Sent: Monday, January 09, 2006 5:09 AM
> To: Discussion of AM Radio
> Subject: Re: [AMRadio] 7285Kc tomorrow/Saturday
> 
> Mark K3MSB wrote:
> 
> >Yes.  I've tried a scope now and then (I have an
> old 60 Mhz B&K), but
> >truthfully I've never been able to really see when
> the modulation
> >level is 100% or other.  I know what ideal
> waveforms look like (with
> >test inputs),  but I have a hard time with a
> typical speech waveform. 
> > I guess if I'm really at 20% that would be fairly
> easy to discern. 
> >When I used the scope before I was trying to figure
> out how to tell if
> >I was say at 70%, 80%, 90% etc,  and never felt I
> could do it
> >accurately.
> >
> 
> Read the John/Don/Bacon page about asymetrical
> audio.  It's written 
> well, it's illustrated well, and completely
> discusses high-level, plate 
> modulated audio and how much you -really- need.
> 
> 
> "Operating your AM Rig with out an oscilloscope,
> is like driving your car at night without
> headlights."
> (-K4KYV/Don Chester - AM Press Exchange)
> 
> ---
> 73 = Best Regards,
> -Geoff/W5OMR
> 
>
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