[time-nuts] notch filter for close in phase noise measurement
adrian.rus at broadhurst.ro
Sun Oct 2 12:05:12 EDT 2016
Why hunt goose with the cannon? The post is about a simple(r) crystal notch filter, nothing more and nothing less. It is not about notch filters (in general) against quadrature method, nor about number of RF components or about their noise floor limitation.
It is about this notch filter against other notch filters.
As per simplicity, to mix 2 oscillators in quadrature one need the second oscillator, the high level mixer, the PLL and the baseband (FFT) analyzer.
Sent from my BlackBerry 10 smartphone on the Orange network.
From: Richard (Rick) Karlquist
Sent: Sunday, October 2, 2016 18:35
To: Discussion of precise time and frequency measurement
Reply To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] notch filter for close in phase noise measurement
On 10/2/2016 12:56 AM, Adrian Rus wrote:
> Hello list,
> For those of you interested in phase noise measurement without using fancy/dedicated gear,
There is no free lunch here. The crystal has its own
intrinsic flicker of frequency noise. You cannot
measure below this noise floor. The technique
you are talking about could be useful in particular
applications, but is not a general replacement for
"dedicated gear". I don't even see where this is
simpler than mixing two oscillators in quadrature.
In that case, the only RF component is a mixer and
everything else is audio. Also, when using a crystal
filter, you have to be careful not to overdrive the
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