[time-nuts] Phase noise measurement (was - no subject)

[EWKehren at aol.com]

On all phase noise measurements I use AGM batteries. specially for the  
signal source to be measured. Keep six 12 V  batteries for that around,  every 
thing from 7 to 20 Amps.
Bert
 
 
In a message dated 8/21/2010 7:33:57 A.M. Eastern Daylight Time,  
bruce.griffiths at xtra.co.nz writes:

The  Wenzel Audio amp is a little noisier than it need be and it has a 
poor  PSRR, so that a very low noise power supply with low ripple is  
essential.
Its not too hard to improve the PSRR and the input noise of  such a 
current feedback amplifier.

There are JFETS (IF9030) with  similar noise floors and significantly 
lower flicker noise.
However the  minimum order from Interfet is about $250.
For noise measurements on  several JFETS (including the IF9030 and the 
2SK369)  see:
"/Ultra-Low-Noise High Input Impedance Amplifier for Low-Frequency  
Measurement Applications/"
Felix A Levinson, IEEE Transactions on  Circuits and Systems Vol 55 No 7, 
August 2008  pp1815-1821.

Bruce

EWKehren at aol.com wrote:
> Hi
> I  have the Hp phase noise system with the 35601A but use most the time  
the
> Wenzel Audio Amp referred to in this email. Perfect! I drive with  it a
> 3561A and  a 7L5!  Works for me.  The only problem  is getting any more 
2SK369.
> Any recommendations?
>  Thanks   Bert Kehren
>
>
> In a message dated  8/20/2010 6:54:05 P.M. Eastern Daylight Time,
> jmiles at pop.net  writes:
>
>
>    
>>   Would  anyone else like to suggest a known good low phase noise
>>  buffer  amplifier?  Maybe something from a Fred Walls  paper?
>>      
> You can  always build HF  isolation amps by rigging MMICs and attenuators
> together,  but  this will not reliably get you below -160 dBc/Hz.  Bruce 
G.
>  has  given some good advice in this regard, with some circuit  designs  
at
> http://www.ko4bb.com/~bruce/IsolationAmplifiers.html  and  elsewhere.  
I'm a
> fan of this version (also from   Bruce):
> http://www.ke5fx.com/norton.htm
>
> This one has  the advantage  of simplicity.  No weird parts, nothing that 
 is
> likely to be out of  production or hard to find, and dirt  cheap.  I've
> measured the  broadband floor at near -170  dBc/Hz at 10 MHz, and its 
noise
> contribution  at 100 Hz is below  what the 3048A can see.  These figures 
are
> adequate  to  measure any 10811-class OCXOs.
>
> A practical PN measurement  system for  10811-class oscillators can be 
made
> by
>  building two of those amplifiers and  using them to drive pretty much  
any
> random double-balanced mixer found on  eBay with +10 dBm LO  specs or 
more.
> Both ports should be driven strongly to  reject AM  artifacts and avoid
> degrading the excellent noise floor offered   by the amps.  I'd hit the LO
> port with +10 to +12 dBm and the RF  port  with at least 0 dBm.
>
> Then, see the Wenzel app note  here  (
> http://www.wenzel.com/documents/measuringphasenoise.htm )  to lock the  
two
> oscillators in quadrature and amplify the  resulting baseband  output.  
Any
> of
> several  sound-card FFT programs can be used to  generate an output graph,
>  although if you want absolute calibration in  dBc/Hz you need to be  
prepared
> to sweep the actual test setup from mixer  output to FFT  input to watch 
for
> various sources of flatness   error.
>
> A combination of an AD7760-EVAL board and a Digilent  Nexys2 can  be used 
to
> construct an excellent baseband digitizer  for the DC-1 MHz  spectrum, but
> most of the time a good-quality  192-kHz sound card is fine  for this 
sort of
> work.  Most  good crystal oscillators reach their  broadband floor by 10 
kHz,
>  so there's no real need to go out to 1 MHz or  more.
>
> --  john,  KE5FX
>
>
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