[time-nuts] PM-to-AM noise conversion (was RE: New Question onHP3048A Phase Noise Test Set)
mfeher at eozinc.com
Thu Jan 17 16:55:17 EST 2008
Here I go again. Martyn defined how he was generating the 100 Hz beat note.
So, not much to assume in this case. -
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bruce Griffiths
Sent: Thursday, January 17, 2008 4:46 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] PM-to-AM noise conversion (was RE: New Question
onHP3048A Phase Noise Test Set)
John Miles wrote:
> I see what you mean, Bruce, but why are the two sidebands considered
> incoherent, just because they're noise? Since the IF is 0 Hz, the other
> sideband appearing at the analyzer input jack is a folded image of the
> noise spectrum, right? Given that, shouldn't the SSB correction be -6 dB
> rather than -3 dB?
The phase angle between the USB and LSB noise components is random when
translated to baseband so when averaged over time the resultant
amplitude is the same as if one just added the powers of the 2 components.
When the 2 sidebands are coherent the phase shift between them is fixed
so that their amplitudes add (vectorially).
The phase angle between the LSB and USB components when translated to
baseband depends on the modulation mechanism creating them.
With both LSB and USB components translated to baseband one has no
additional information so that some "reasonable" assumption has to be made.
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