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phase noise analyzer and phase noise measurement

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nctnico:
Problem is that I don't run Windows natively. For a slow process like Timelab that isn't much of a problem but feeding a USB3 datastream into a VM looks like asking for trouble. I prefer to avoid Windows based software as Windows doesn't fit my computer usage.

Anyway, the time deviation graphs don't look that stellar compared to a standalone DMTD unit I have under development.

cncjerry:
the developer referenced Andrew Holme's work.  I built Andrew's system and it works great.   I got lots of help from Andrew and Adrian Rus who went over the top to assist me. 

I needed to use batteries for the runs in addition to low noise LDO regulators.  Even with clean power supplies (and the LT3045 regulators) I still had some noise.  So I'm surprised the performance is so good on this unit with USB power. Andrew's system only uses USB for control of the FPGA and then 1Gig ethernet for the data feeding the PC plotting system. 

The expense is in the references, filters before the ADCs, the DAC oscillator and the shielding and positioning of the equipment in the lab. I had the best results using Dewalt 20v batteries stepped down with the LT regulators.  Adrian made some mods to his ADC board that worked better for him.  The other factor that came into play was the interaction of the ADC clock and the DUT as well as the reference oscillators.  Adrian developed a spreadsheet that calculated the interaction of the reference, DUT and ADC clock but the bottom line is you want the harmonics and mixing to not produce a spur within the measurement range.  I think that is an adequate explanation.   the last reference oscillators I used were at 26Mhz made by Wenzel with Minicircuits filters at 27Mhz.  Then I remember getting designs from someone for non-reflective filters.  Most of this is on Andrew's site that which I highly recommend.

Adrian then sent me some other oscillator links that I was yet to implement though I acquired them.  Given you don't need (or want) references at 10Mhz in many cases, you can move onto other odd frequencies like I did at 26Mhz.  But I think the 26Mhz interacted with my ADC clock, so I then acquired one that is phased locked to 10Mhz but generates 118Mhz and change.  You also have to setup the ADC to accept the correct clock (in Andrew's implementation) and it must be clean with low jitter.  The limit on the ADC Andrew used was 125Mhz. 

One other point, in order to get the maximum performance you need to bring the DUT and references up to the ADC limits.  I ended up spending a lot of money on QB188 amps and attenuators. I used fixed attenuators as well as variable controlled by my HP70K system.

The bottom line is that to get to a clean -185 noise floor takes a lot of screwing around.  But considering you can do it for substantially less money (under $2,000 for Andrew's) implementation assuming you get the SP605 spartan6 FPGA used, and it compares to units costing 10x that number, I thought it was a good deal.  Andrew's unit didn't do ADEV work or interface directly with Timelab the last time I updated it.  But you can dump the data into Timelab, matlab, Stable32, etc.  I use another entire system for ADEV work anyway.

I never thought I could get that level of performance for such a modest price.  You can get it going for under $750 USD and then build it up from there.

Jerry

alan.bain:
Did you use the Spartan 6 eval board as in AH's write up?

I got the impression that supply chain problems (or rather fab capacity) had effectively forced Spartan 6 out of the market but possibly this was only supply affecting production of new designs rather than eval boards.

I read AH's excellent write up and found the approach very interesting, especially the cross-correlation trick with two independent input chains to improve the measurement noise floor. Part of me likes the idea of a 3048 with all those nice HP boxes, but probably the digital approach will get better results.

cncjerry:

--- Quote from: alan.bain on May 12, 2023, 10:12:30 pm ---Did you use the Spartan 6 eval board as in AH's write up?

I got the impression that supply chain problems (or rather fab capacity) had effectively forced Spartan 6 out of the market but possibly this was only supply affecting production of new designs rather than eval boards.

I read AH's excellent write up and found the approach very interesting, especially the cross-correlation trick with two independent input chains to improve the measurement noise floor. Part of me likes the idea of a 3048 with all those nice HP boxes, but probably the digital approach will get better results.

--- End quote ---

The 3048 has many challenges but I know people who struggled through it.  I guess the software is the biggest problem.  But I've never seen a noise floor approaching that of Andrew's on a 3048.  Maybe I've just not seen it, but it is considered an old technology that can't compete with the cross-correlation approach.  But it is cool.

Use this: https://www.ebay.com/itm/204033950500

Jerry

One other point, I purchased the kitted-out reference oscillators from a 3048 system and they barely made it to -155 at 100k, IIRC. 

I checked my plots and the A5 reference was -155 or so and the A6 was -165 with my noise floor at -185 so the analyzer was the limit.  What I don't understand is all the pictures I've seen on the web have the floor for the 3048 at around -170 if not higher yet I have a friend who built two systems, using the HP references, and he reported deeper than that, down around -180.  I would look at replacing the references as you can get Wenzel sprinter series (500's and 501's) at 10Mhz that are 10db better if not 20.  You have to check as the Wenzel 501 series are standard parts and you can get their PN specs.  the 500 series you have to test and I have some that have very good performance for less than $50USD per, not as good as their ULN series but 1/10th the price.

One last comment, it doesn't take much equipment to measure PN at one frequency as outlined in the HP memory project here:

https://www.hpmemoryproject.org/technics/bench/3048/pn_measrmt_single.htm

Granted you aren't going to get a nice plot without some GPIB automation but still, a couple amps, a low pass filter or two, a reference and Bob's your uncle.

Jerry

jhenderson0107:

--- Quote from: jhenderson0107 on April 28, 2023, 06:33:25 pm ---The biggest limitation I've encountered thus far is that its analog front-end is bandwidth limited to  < 1 GHz....
--- End quote ---

Following up on my earlier comment: 

I've eliminated the above bandwidth restriction restriction by assembling two 10 MHz Wenzel Streamline oscillators, a Wenzel LNAF amplifier-low pass filter and M/ACOM M8TC mixer into a small chassis.  The oscillators provide very good low-phase noise references to the PN2060A.  The clock output of my R&S generator is used as the LO to the mixer+LNAF, which down-converts the DUT to 10 MHz without any significant phase noise performance reduction.  Consequently, the bandwidth of the system is now extended to 3.4 GHz, which meets my current needs. 

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