[time-nuts] PM-to-AM noise conversion

[John Miles]

Yeah, that was totally it:
http://www.thegleam.com/ke5fx/spur_demo.gif

The spur amplitude accuracy is at its best in the red trace, just before the
LNA starts to distort.

Martyn: see if the amplitude of the spur you inject has any effect on the
apparent inaccuracy of the 3048A.  LNA misbehavior could still be affecting
your measurement, even though you're not looking at an FM'ed source.

Alternatively, try the same measurement without the 3048A's LNA switched in,
if you can?

-- john, KE5FX


> Ah... that could very well be the case.  The second lobe is so
> weak relative
> to the first, that it's very easy to believe that harmonics
> generated in the
> LNA were stronger.  I'll bear that in mind when re-checking the
> measurement.
> Sounds like another win for Occam.
>
> -- john, KE5FX
>
> > -----Original Message-----
> > From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> > Behalf Of Bruce Griffiths
> > Sent: Thursday, January 17, 2008 5:11 PM
> > To: Discussion of precise time and frequency measurement
> > Subject: Re: [time-nuts] PM-to-AM noise conversion
> >
> >
> > John
> >
> > A simpler and more prosaic cause is distortion in the post phase
> > detector amplifier.
> > If this amplifier sees enough of the modulation frequency fundamental
> > component,
> > it could conceivably produce enough second harmonic by itself to produce
> > the observed effect.
> >