Re: [time-nuts] Minicircuits SYPD-1

[Gerhard Hoffmann]

Hi,

matching in the sense of selecting 4 equal ones won't help much with BJTs.

Take them from the same tape, that's enough. Also, the transformer ratio

does not matter much. Once VBE = 0.7V, the transistors switch on. The 
authors


write that thy use the BE junction as diodes, but that is not true. The 
transistors


are operated as switches. That's probably the reason why they are so good.

A different transformer ratio only shifts the level where the 0.7V Vbe 
is reached;


a dB more or less, not a big thing.


The power required for optimum return loss seems to be quite precise.

If you do not have enough for Vbe=0.7V, the switches will sit there 
idle, giving


bad return loss; having too much pumps a lot of current through the ring and

the mismatch will be to the short circuit side.

You could also drive them somewhat into saturation which would make

them slow. That's why I used a fast-ish transistor from the start.


In my case, 8 or 10 dBm made quite a difference from the 9dBm for 
optimum BW.


I have some MCL T1-6 and could check them over the weekend.


If you have more signal power, it's probably wise to split it to more PDs

and add the IF outputs.  This here seems to be an interesting Wilkinson:

<   https://www.digikey.de/products/de?keywords=1465-1815-1-nd    >

So it all boils down to el cheapo coils and Schnaps or beta-blockers for 
soldering.



In the case of JFETs as switches, your curve tracer could probably help 
a lot.


JFETs are all individuals, see Ic over Vgs for IF3601 / IF3602

< 
https://www.flickr.com/photos/137684711@N07/37321004540/in/album-72157662535945536/ 
   >



The IF3601 is a large geometry JFET with huge gm, that can deliver 0.3 
nV/rtHz voltage noise.


Four of them in parallel yield 160 pV/rt Hz; I could verify that but 
they were not


completely stable for inductive signal source impedance. If you want to 
simply parallel them,


one of them might happily sink 1A while the other is still completely 
cut-off.


They also seem to need more drain current than promised and the IF3602 duals

are not pairs in the closer sense. But no opposite outliers, OK.   
(avail. @ Mouser)



My newest creation uses a bootstrapped cascode to effectively remove the 
LARGE


input capacitance; that also seems to make it unconditionally stable, at 
least in simulation.


The new boards are spending this week in the Leipzig, DE customs office 
since someone


does not believe that PCBWAY in China can deliver 10 proto boards for 
$5.  :-[



Having such an amplifier after a ring mixer is probably overkill; a RF 
Schottky diode


may have easily a ohmic 50 Ohms component in series and two of them 
active in a ring


mixer guarantee 1.3 nV/rtHz thermal noise alone. (and that is NOT the 
half-thermal slope


resistance of the diode effect itself)


High power type3 ring mixers have additional resistors in series to the 
diodes to create


some back-bias. Those also create noise and so it should not come as a 
surprise that


high power mixers may be kings of IP3 but lose big time at the noise end 
of the scale.


< 
http://home.deib.polimi.it/svelto/didattica/materiale_didattico/materiale%20didattico_MRF/appnote/wj_Mixers_part_2.pdf 
   >



regards, Gerhard


Am 20.12.18 um 03:16 schrieb Jerry Hancock:

Gerhard, would there be any advantage to matching the transistors?  I have a 
pretty accurate curve tracer.

thanks,

Jerry




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[Eric Scace]

Warning: websites cited here can be seriously time-consuming rabbit holes!

   An anonymous engineer using the pseudonym NwAvGuy 
 got fed up with the subjective nature of 
discussions about DACs and amplifiers in the world of high fidelity audio. To 
clear away the smoke, in 2011 he started publishing independent measurements, 
along with some blog posts about what measurements and goals were detectable. 
As one might imagine, this was very controversial.

  Later that year he (or she) concluded it was possible to build a replicable 
DAC and a headphone amplifier 
 that could exceed the 
performance of so-called high-end units being sold for 10e3 - 10e5 dollars, yet 
cost the consumer an order of magnitude less. His blog posts describe the 
design process from requirements to finished result.

   Relevant to this thread was NwAvGuy’s long list of PC board routing and 
enclosure topics that significantly affect performance of otherwise identical 
parts and circuit:
ground routing, ground planes, floods & fills
EMI loops
inductive coupling
parasitics
failure to follow the PC layout developed by the component manufacturer
component placement, aka “rows and columns may not be your friend”
track placement: moving a single track can change increase distortion [by 26 
dB] was one example given
all this at audio frequencies.

   So, yes, I cringe at the thought of developing such systems at frequencies 
and performance levels we talk about here on Time-Nuts. There are not enough 
lifetimes to learn how to do this well, I feel. :-(

   Hats off to all those people who’ve mastered and advanced this craft.

— Eric K3NA

p.s.: NwAvGuy’s resulting DAC/amp has been available in kit or assembled form 
since 2012 from companies such as JDS Labs 
 ($280), built 
exactly according to the design spelled out by NwAvGuy.
   NwAvGuy’s identity has been closely guarded by the few individuals who know 
it. (I am not one of those.) She stopped posting in 2012 and disappeared from 
the scene.
   More recently, Audio Science Review 
 has started publishing 
objective measurements of commercial audio equipment, including DACs 

 and headphone amps 

 that somewhat exceed the performance of the NwAvGuy’s solution but remain in 
similar price ranges. The site’s admin and principle author employs a pseudonym 
amirm , 
claims to be in the Seattle area — and some wonder if this is the same person 
as NwAvGuy.

> On 2018 Dec 20, at 01:41 , ed breya  wrote:
> 
> Yup, I've seen plenty of "top cover effects," and other strange things. That 
> sort of thing is evident even when you don't have to reach E-12 resolution 
> levels - like a million times less. The instrument cabinet and hardware are 
> indeed a part of the electronic system and circuits. So are what it's hooked 
> up to, and its various characteristics, and so on.

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[time-nuts] Trimble NetRS PPS output

[Mark Sims]

I recently got in a Trimble NetRS L1/L2/L2C survey grade receiver (Evil Uncle 
Bob made me do it ;-)  ).   It consistently gives position error ellipses in 
the 6mm range after post-processing 24 hours of data.

I had high hopes it would have a decent 1PPS output...  nope.  The PPS output 
usually has a 40 nsec span (looks like a 25 MHz clock is in the device), with 
some occasional 80 nsec or so spans.  The internal oscillator looks to be an 
OCXO... the PPS does not show your typical wobbly PPS sawtooth error plots.  It 
is more like a pulse train with a slowly drifting duty cycle.

But the killer is the occasional (2-3 times per hour) "zingers" in the PPS 
output.  These show up as a large negative error spike followed immediately by 
an equal positive errors.   These "zingers" are typically in the 1-100 
millisecond range.   I can't imagine how/why the circuitry would do this...

Lady Heather can now monitor the NetRS (and probably other receivers that can 
output RT17 and Trimcomm data.   The NetRS does not respond to requests for 
status and configuration commands over the RT17 ports, so a lot of 
useful/informative stuff is not available.  It can write RINEX files.___
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Re: [time-nuts] Trimble NetRS PPS output

[Mike Cook]

This doesn’t surprise me. Some years back I thought I could get better PPS 
resolution from a survey grade receiver but was disappointed to find on looking 
at specs of those available that PPS performance was generally worse than 
timing receivers, which of couse were much cheaper. It’s a no brainer now with 
sawtooth error correction available.

> Le 21 déc. 2018 à 05:05, Mark Sims  a écrit :
> 
> I recently got in a Trimble NetRS L1/L2/L2C survey grade receiver (Evil Uncle 
> Bob made me do it ;-)  ).   It consistently gives position error ellipses in 
> the 6mm range after post-processing 24 hours of data.
> 
> I had high hopes it would have a decent 1PPS output...  nope.  The PPS output 
> usually has a 40 nsec span (looks like a 25 MHz clock is in the device), with 
> some occasional 80 nsec or so spans.  The internal oscillator looks to be an 
> OCXO... the PPS does not show your typical wobbly PPS sawtooth error plots.  
> It is more like a pulse train with a slowly drifting duty cycle.
> 
> But the killer is the occasional (2-3 times per hour) "zingers" in the PPS 
> output.  These show up as a large negative error spike followed immediately 
> by an equal positive errors.   These "zingers" are typically in the 1-100 
> millisecond range.   I can't imagine how/why the circuitry would do this...
> 
> Lady Heather can now monitor the NetRS (and probably other receivers that can 
> output RT17 and Trimcomm data.   The NetRS does not respond to requests for 
> status and configuration commands over the RT17 ports, so a lot of 
> useful/informative stuff is not available.  It can write RINEX 
> files.___
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Knowledge is a great weapon but a poor shield.


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Re: [time-nuts] HP Cesium Standards in the International Atomic Time Scale, the legend of Felix Lazarus, and the "top cover effect".

[Magnus Danielson]

Dear Hugh,

I really enjoyed reading this! You have several cliff-hangers in there:
Did you (HP) fix/reduce the top cover issue? Did you alter the setup to
meet tighter specs? Did you fix the oven controller cable offset?
What else war-stories do you got?

It is by war-stories one shares knowledge, lessons learned is not
without its background and at least you have a great story.

Cheers,
Magnus

On 12/20/18 12:36 AM, Rice, Hugh (IPH Writing Systems) wrote:
> Hello Time Nuts,
> I found this HP Application note in my archives, and attached a scanned copy:
> 
> Application Note 52-4.  Contribution of HP clocks to the BIH's International 
> Atomic Time Scale (IATS).
> I also found a couple of archives for HP application notes for anyone who may 
> be interested:
> http://hparchive.com/appnotes
> https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1127547&id=1127547&cmpid=zzfindclassic-app-notes
> 
> 
> It is an interesting snapshot at the method of keeping the official IATS 
> time, and how HP Cesium standards are a major part of it, published in 1986.
> 
> The author, Felix Lazarus, was a legendary Field Application Engineer (or 
> something like that) for HP in Europe, based in Geneva Switzerland.   He was 
> obsessively fussy, and insisted that any Cesium Standard shipped to key 
> customers in Europe were first shipped to him, so he could verify acceptable 
> performance before the customer received the instrument.
> 
> He would fire up the product, re-tune and re-align all the settings, and then 
> compare it to his house standard.  If it wasn't up to his exacting standards, 
> he would keep tuning and testing until it was acceptable - to him.He was 
> looking for performance several times better than our published 
> specifications, which were 5 x 10e-12.   He wasn't satisfied until is was 
> less than 2, or something like that.It drove us factory guys crazy.   He 
> was a well-respected figure in the time keeping world, and would bash us for 
> shipping product that were not beating the specs by enough margin.
> 
> I think he is the one that discovered the "top cover effect".  If you removed 
> the top sheet metal cover from the instrument, the offset would shift by a 
> part in 10 to the 12th or so.   If you put the cover on, and changed how 
> tight the screws were tightened, it would shift differently.   I recall he 
> wanted us to fix this.
> 
> I was the "Production Engineer" on the Cesium standards, a young BSEE college 
> graduate.   I barely knew how a basic op-amp amplifier worked, and was 
> completely overwhelmed by the complexity of the Cesium Standards.   "Go fix 
> the problem on the most accurate commercial atomic standard for sale in the 
> world, where if you change how tight a screw is, the performance shifts a 
> touch."   It is safe to say that I didn't make this my highest priority.
> There were theories that the root cause was subtle changes to the ground 
> loops with a change like this.   The whole product used all the sheet metal 
> as a common ground, meaning that the ground return paths were not designed at 
> all, just left to chance.
> 
> A related issue that I didn't work on was the "oven controller cable offset." 
>   There was a big multi wire cable o the cesium oven heater controller, and 
> if you twisted it left vs. right before plugging it in, the offset of the 
> standard would change.
> 
> 
> Working on the 5061B destroyed my confidence in my engineering abilities.   I 
> didn't think I could solve "real" engineering problems, because of issues 
> like this.After working on the 5061B product for several years, I applied 
> for a job as an engineering manager over the frequency counter production 
> product line.  During the interviews, my low technical self-confidence came 
> through, and the R&D management partners to this position were worried I 
> couldn't provide technical leadership to the other engineers.So, in true 
> HP fashion, my they sent me through the full scale HP R&D engineering 
> interview -about a half dozen deep 1:1 technical interviews with EE experts 
> in the lab.   Turns out that I wasn't a dunce after all, just scarred from my 
> experience working on the cesium standards.   I got the job.
> 
> 
> I have a handful of other stories like this from my days inside HP frequency 
> and time division.Let me know if you want to hear more.Maybe Rick 
> Karlquist will tell some stories of developing the 5071!
> 
> Hugh Rice
> 
> 
> 
> 
> 
> 
> 
> 
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Re: [time-nuts] Minicircuits SYPD-1

[Magnus Danielson]

Hi Jerry,

On 12/19/18 7:04 PM, Jerry Hancock wrote:
> Thanks to all that replied, lots of good info which will take me months to 
> sort through, especially the link to Jürg Kögel looks helpful as well as a 
> note from Bert.
> 
> Attila, Yes, more phase noise than long term though this is really an 
> exercise to get a better understanding of oscillators and measurement 
> techniques.
> 
> The 2n mixer sounds like another H-mode, I’ll have to look at it.  It 
> probably uses self-wound, micro-sized bobbins which will be a challenge for 
> me :-].

No, it used off the shelf transformers and the 2NA hooked up in
diode mode in a ring, just as you would for a DBM, it's home-cooked DBM.
Check it out for yourself:
https://tf.nist.gov/general/pdf/2554.pdf

Do use the NIST Time and Frequency library with all their articles, lots
of fun reading ahead!

> Bob, I think you were the person who pointed me to the loose PLL a while 
> back.  The circuit I am building used a gain of 300ish (30k/100) and I expect 
> that to really clip when unlocked.  I have a 10-turn variable in the circuit 
> to bring it close initially. 

The gain in one stage in itself is not particular interesting, but
rather the loops open-loop gain which translates into the bandwidth of
the loop.

Cheers,
Magnus

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