[time-nuts] Very challenging phase noise measurement, does anyone have an idea??

Bob Camp lists at rtty.us
Thu Dec 6 01:48:14 UTC 2012


Hi

You might be surprised by the noise floor of an XOR run at 125 KHz. They are quite good at that low a frequency. 

Bob


On Dec 5, 2012, at 8:24 PM, John Miles <jmiles at pop.net> wrote:

> That would be a good way to do it.  I wouldn't use an XOR gate or other
> digital phase detector for this, due to the low slew rate among other
> things.  Instead, you could phase lock two of your sources with a
> double-balanced mixer, then run the IF through a lowpass filter and a quiet
> opamp or other LNA.  The baseband noise can then be viewed on a spectrum
> analyzer that goes down to whatever the minimum offset of interest is.  The
> analyzer's noise floor doesn't matter, it just needs to be something that
> can tune down to the 100 Hz-1 kHz area.  An old-school HP 8566 or 8568 is
> ideal.
> 
> For calibration details, see the references in the last FAQ entry at
> http://www.ke5fx.com/gpib/faq.htm , especially HP 11729B-1. 
> 
> Alternatively, I'm not sure where the noise floor of the FSUP is, but if it
> is otherwise low enough, you could mix the 125 kHz with an ultra-low-noise
> OCXO and measure one of the resulting sidebands.  It might or might not be
> necessary to filter the other sideband depending on how the FSUP works. 
> 
> You could also build a low-noise 8x active multiplier to get to 1 MHz where
> the FSUP can see it, as well.  This would have the advantage of not
> requiring a ULN OCXO for mixing, and would also boost the PN by 18 dB for
> easier measurement on the FSUP.  However, you'd need to be careful with the
> multiplier's residual noise, especially in the first couple of stages.  
> 
> If you need to make these measurements over and over, go with the multiplier
> or mixer, otherwise I'd use an analog quadrature PLL.
> 
> -- john
> Miles Design LLC
> 
> 
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-
>> bounces at febo.com] On Behalf Of Adrian
>> Sent: Wednesday, December 05, 2012 4:40 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Very challenging phase noise measurement, does
>> anyone have an idea??
>> 
>> You can always use an external mixer / phase detector and the baseband
>> input of a HP 3048A or FSUP.
>> 
>> Just to name a few:
>> For low power (+7dBm) you can use a SRA-3 which goes from 25kHz to
>> 200MHz
>> SRA-3MH +13dBm from 25kHz to 200MHz
>> SRA-3H +17dBm from 50kHz to 200MHz
>> For high power signals use a RAY-3. It goes from 70kHz to 200MHz.
>> The IF must be specified from DC, which for the above is the case.
>> 
>> Between mixer and baseband input a lowpass filter is required to
>> suppress the sum signal (2x f_input) sufficiently.
>> 
>> Adrian
>> 
>> 
>> Azelio Boriani schrieb:
>>> Yes, I have taken a look and the FSUP is 1MHz min at the signal
> analyzer.
>>> Timepod? No, 500KHz min... an R&S FAM modulation analyzer?
>>> 
>>> On Wed, Dec 5, 2012 at 10:48 PM, Bob Camp <lists at rtty.us> wrote:
>>> 
>>>> Hi
>>>> 
>>>> A "3048" style measurement with the carrier suppressed by lock should
>> do
>>>> pretty well. If the XOR's are out, there are a lot of mixers available
> that
>>>> work at 125 KHz. A simple op-amp buffer and a sound card could do what
>> you
>>>> need to do.
>>>> 
>>>> Bob
>>>> 
>>>> -----Original Message-----
>>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-
>> bounces at febo.com] On
>>>> Behalf Of Adrian
>>>> Sent: Wednesday, December 05, 2012 4:33 PM
>>>> To: Discussion of precise time and frequency measurement
>>>> Subject: Re: [time-nuts] Very challenging phase noise measurement,
>> does
>>>> anyone have an idea??
>>>> 
>>>> For phase noise the frequency range is 1MHz to 8/26.5/50GHz
>>>> The spectrum analyzer works from 20Hz to max.
>>>> 
>>>> Adrian
>>>> 
>>>> 
>>>> Azelio Boriani schrieb:
>>>>> Isn't the FSUP a 110K euros equipment 20Hz-50GHz capable? 125KHz
>>>> shouldn't
>>>>> be a problem. I had an FSUP for 25 seconds to play with... really
>>>>> impressive but too limited test time to appreciate fully.
>>>>> 
>>>>> On Wed, Dec 5, 2012 at 1:14 PM, Bob Camp <lists at rtty.us> wrote:
>>>>> 
>>>>>> Hi
>>>>>> 
>>>>>> Just about any of the high speed CMOS parts should work. A 74AC86 is
>>>> about
>>>>>> the earliest part I would trust. Any of the fast logic families that
>>>> came
>>>>>> after that should do equally well.
>>>>>> 
>>>>>> Bob
>>>>>> 
>>>>>> On Dec 5, 2012, at 7:03 AM, Hans Rosenberg <Hrosenberg at catena.nl>
>>>> wrote:
>>>>>>> Hello Time-nuts,
>>>>>>> 
>>>>>>> I have to do a phase noise measurement and I'm wondering if anyone
>> here
>>>>>> has any ideas on that. We have to measure the phase noise of a 125kHz
>>>>>> carrier (5Vp-p signal level). The measurement system should have a
>> noise
>>>>>> floor that is -164dBc/Hz at a distance of 1kHz to 8kHz away from the
>>>>>> carrier.
>>>>>>> Our current plan is to use 2 of these sources, have one in free
> running
>>>>>> mode and lock the other one to the first one using an XOR gate and
>> then
>>>> use
>>>>>> the output of the XOR gate as an output signal. However, we are
>>>> wondering
>>>>>> if any of you know a better idea. Maybe there is an off-the-shelf
> piece
>>>> of
>>>>>> equipment that can do that that we could rent. Or maybe we could
>>>> increase
>>>>>> the frequency to a few megahertz using a pll, which means the signal
>>>> comes
>>>>>> into the measurement range of our FSUP phase-noise analyzer.
>> Problem is,
>>>>>> the phase detector would then need to have an insanely low noise-
>> floor
>>>> (in
>>>>>> our idea the XOR also has to have this insanely low noise floor as
> well
>>>> off
>>>>>> course) so does anyone have experience with anything like this? Does
>>>> anyone
>>>>>> know an XOR with these good specs? I don't have a clue what a
>> standard
>>>>>> 74lvc1g86 would do. Needless to say the supply of this XOR would have
>> to
>>>> be
>>>>>> ridiculously clean, but I do have a solution for that problem.
>>>>>>> Any help is greatly appreciated!
>>>>>>> 
>>>>>>> Best regards,
>>>>>>> 
>>>>>>> Hans Rosenberg
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