[time-nuts] Ultra low phase noise floor measurement system for RF devices.

[Magnus Danielson]

From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] Ultra low phase noise floor measurement system for RF devices.
Date: Sun, 01 Apr 2007 16:30:31 +1200
Message-ID: <460F3567.80605 at xtra.co.nz>

> Magnus Danielson wrote:
> > In the article that was recently referred to, it was not a measurement rig for
> > oscillators but for transfer components, such as gain-stages, phase shifters
> > etc. and the approach is different then, since you do have the signal prior to
> > being dirtyfied. Thus, the interferometer approach makes sense. The refinement
> > was certainly interesting.
> >
> > Cheers,
> > Magnus
> >   
> Hej Magnus
> 
> What about a 3 source version of the following with the oscillator under 
> test common to both channels together with using the cross spectrum to 
> isolate the noise due to the oscillator under test. (of course phase 
> locking the 2 other oscillators to the reference using a very low 
> bandwidth loop may also be required).

Naturally

Now, this would indeed improve the 1/f noise measurement floor of a cross-
correlator setup, but for a fairly low price (thr addition of two hybrid
couplers.

It is really clever in its simplicity, since what you want to measure goes in
arm A (non-flickered amplification) and what you demodulate with goes in arm B
(flickered amplification - but won't demodulate unless you have _strong_
sidebands and then this technique is of no interest anyway - a spectrum
analyzer does the job then).

My concerns is rather about the hybrid coupler and frequency range. This work
was on 9.9 GHz but what if I would like a more moderate frequency but a wider
range (1 MHz to 1 GHz or so)? Ah well, this comment only discloses that I don't
mess around enought in analog RF too much.

I've learned a few new usefull things from the recent discussion on Rubiola
(hey! Welcome!) papers! This little two-pagers should have come first up
thought, since it in its simplicity contains one of the basic ideas which the
more elaborate papers builds upon.

Cheers,
Magnus