[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)

[Bob kb8tq]

Hi

> On Jul 5, 2022, at 9:00 AM, Erik Kaashoek via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Mike.
> One concern I have with active components as mixer is noise. For an SA I
> designed only a passive DB diode mixer had low enough output noise. Would a
> PF detector as being an active component, not create more noise as output?
> Erik

Yes, you are correct. The only thing with a low enough noise floor for good
phase noise measurements (via the quadrature technique) is some sort of mixer.
Normal digital phase detectors have way to high a noise floor.

Bob

> 
> On Tue, Jul 5, 2022, 18:20 Mike Monett via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>> You stated:
>> 
>> Mike,
>> The phase detector is an ADE-1 mixer, the IF output of the mixer goes
>> into a loop filter that has a corner frequency of about 0.2Hz to enable
>> Phase noise measurements down to 1Hz offset
>> 
>> That is your problem. A double balanced mixer is an exclusive-or phase
>> detector. The lock range is determined by the loop bandwidth, as you have
>> found.
>> 
>> The phase-frequency detector is completely different. It will lock to any
>> signal in the lock range, independent of loop bandwidth. You can have a
>> bandwidth of 0.001 Hz, and it will still lock. Think of what this could do
>> for your phase measurements.
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