[time-nuts] Phase noise measurement (was - no subject)
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Sat Aug 21 11:33:30 UTC 2010
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
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
More information about the time-nuts
mailing list