[time-nuts] Stepping up the output of an OCXO

Ulrich Bangert df6jb at ulrich-bangert.de
Sun Feb 4 05:47:09 EST 2007


I have seen this specs before but do you know how to find the

Best regards
Ulric Bangert

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Dr Bruce Griffiths
> Gesendet: Sonntag, 4. Februar 2007 08:32
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Stepping up the output of an OCXO
> John Ackermann N8UR wrote:
> > I had a chance to measure a TADD-1 using an HP-3048 phase 
> noise system 
> > last year.  I've attached a screen shot of the results; in short it 
> > was below -140dBc/Hz from 100 Hz on out (by the way, I'm not sure I 
> > would trust the noise floor shown in this test; I am not certain we 
> > had the best test set-up).  That's within a few dB of what HP said 
> > their 5087A amplifier would do.
> >
> > I'll soon have access to a new phase noise measurement 
> system and will 
> > relook at the TADD-1 performance with it.
> >
> > John
> >
> >   
> John
> My calculations using the component values in the circuit 
> indicate that 
> the TADD-1 noise figure should be about 19dB and its 
> corresponding phase 
> noise floor should be lower than -160dBc/Hz. when the input signal is 
> +7dBm or greater. So unless you had an unusually noisy set of opamps
> and/or resistors the measurement setup phase noise floor probably 
> exceeds that of the TADD-1 by around 20dB.
> With a 10V supply instead of 9V and a +13dBm input the phase 
> noise floor 
> should be about -168dBc/Hz which is respectable but a few 
> (~10) dB shy 
> of the state of the art.
> The only way to achieve the state of the art performance with opamps 
> using a 9 or 10V supply is to use lower noise (2nV/rtHz appears 
> feasible) opamps pairs driven in push pull by an input step up (1:2 
> turns ratio) transformer with an output stepdown transformer 
> driven in 
> pushpull by the 2 opamp outputs. The noisy 1K input 
> protection resistor 
> would also have to be reduced in value as would the opamp feedback 
> network resistors.
> NIST's 1995 distribution amplifier claims a phase tempco of 
> 0.3ps/K and 
> 120dB isolation between channels. 
> http://www.physics.nist.gov/News/Update/950626> .html
> Bruce
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