[time-nuts] Rb vs.Crystal OCXO

Richard (Rick) Karlquist richard at karlquist.com
Fri Apr 25 18:29:38 EDT 2014


My understanding is that a really good Rb standard
use a fairly wide bandwidth loop to control its own
internal XO, and therefore improve its close in phase
noise to be better than you can get with quartz alone.
The Rb standard is able to do this because the S/N
ratio of its rubidium vapor frequency reference (RVFR)
is fairly high, and in any event considerably better
than the S/N out of a CBT.  Also, Rb standards have
much smaller frequency jumps, if any, than quartz.
Phase noise specs conveniently don't include the effects
of jumps.  Newer laser diode pumped Rb standards may
make the comparison even more lopsided.

Rick

On 4/25/2014 9:12 AM, Shane Kirkbride wrote:
> Hi Everyone,
> I'm newer to this forum but I really enjoy reading the discussions. I have
> a pretty basic question.
> I'm wondering why one would chose an Rb Oscillator over a traditional OCXO?
> It does not immediately appear there is a phase noise advantage in the Rb..
> Thanks,
> ~Shane
>
>
> On Fri, Apr 25, 2014 at 10:00 AM, <time-nuts-request at febo.com> wrote:
>
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>> Today's Topics:
>>
>>     1. Low SNR GPS reception and cheap LNAs (Attila Kinali)
>>     2. Re: Symmetricom chip scale atomic clock (Tom Knox)
>>     3. Re: How to accurately measure an oscillator's     temperature.
>>        (Didier Juges)
>>     4. Re: Low SNR GPS reception and cheap LNAs (Chris Albertson)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Fri, 25 Apr 2014 15:28:22 +0200
>> From: Attila Kinali <attila at kinali.ch>
>> To: time-nuts at febo.com
>> Subject: [time-nuts] Low SNR GPS reception and cheap LNAs
>> Message-ID: <20140425152822.203775c003a761042e269c63 at kinali.ch>
>> Content-Type: text/plain; charset=US-ASCII
>>
>> Hi,
>>
>> I recently bought a bladeRF[1] to experiment a bit with GPS decoding.
>>
>> I tried to get GNSS-SDR[2] which seems quite good, but has its flaws.
>> One of the things was that i cannot seem to get a fix in my environment.
>> One of the problems seems that my antenna position is far from optimal.
>> Aparently, GNSS-SDR uses only a very rudimentary acquisition technique
>> (at least so i have been told). Now i wonder what techniques for low SNR
>> acquisition are around. Would someone be so kind and give me some key
>> words to google for?
>>
>> I also am looking to add an LNA to my reception chain, which is a
>> mix of a 50R antenna with 75R Coaxcable (sat coax stuff is just a lot
>> cheaper :-). Has anyone a recomendation for a good LNA that can be used
>> in a flying construction (soldering onto two back-to-back glued
>> connectors)?
>> Ie it shouldnt be a QFN or BGA. DFN works but i'd rather have something
>> with pins, like SC-70/SOT-323 or similar/larger.
>>
>>
>>                          Attila Kinali
>>
>>
>> [1] www.nuand.com/bladeRF
>> [2] www.gnss-sdr.org
>>
>> --
>> The trouble with you, Shev, is you don't say anything until you've saved
>> up a whole truckload of damned heavy brick arguments and then you dump
>> them all out and never look at the bleeding body mangled beneath the heap
>>                  -- Tirin, The Dispossessed, U. Le Guin
>>
>>
>> ------------------------------
>>
>> Message: 2
>> Date: Fri, 25 Apr 2014 08:53:25 -0600
>> From: Tom Knox <actast at hotmail.com>
>> To: Time-Nuts <time-nuts at febo.com>
>> Subject: Re: [time-nuts] Symmetricom chip scale atomic clock
>> Message-ID: <COL130-W35B7069EE8D042E122A563DF5A0 at phx.gbl>
>> Content-Type: text/plain; charset="iso-8859-1"
>>
>> For the sake of discussion let me just add that even if medesigns comments
>> were true of Microsemi, the Microsemi responses on this form have been from
>> long time Time-Nuts who have for years contributed their knowledge to the
>> betterment of the community in the proudest traditions of acadimia. Never
>> have I seen them use the form for financial gain. Sure corporate greed is a
>> problem in todays society but knowing some of the individuals at Microsemi
>> it is clearly not a black and white issue. Further where it may be
>> acceptable in some cases to release a product early and perform some of the
>> final development on the backs of the customers to better serve their needs
>> such as in the case of the fantastic "TimeLab".  In a mission critical
>> product like the CSAC a problem like this will cost Microsemi far more then
>> they would profit from a premature release. These manufacturing defects
>> were clearly something they could not anticipate.   I for one will be
>> purchasing many more Microsemi products
>>   in the future and viewing their performance on TimeLab with full
>> confidence. Please keep the group update on your progress resolving this
>> issue. It will be interesting to see if a single point of failure is found,
>> a smoking gun so to speak; or whether it will be resolved with a number of
>> minor changes during product evolution. In any case I hope the problem is
>> resolved quickly.
>>
>> Thomas Knox
>>
>>
>>
>>> Date: Fri, 25 Apr 2014 08:14:06 +0200
>>> From: attila at kinali.ch
>>> To: time-nuts at febo.com
>>> Subject: Re: [time-nuts] Symmetricom chip scale atomic clock
>>>
>>> On Fri, 25 Apr 2014 08:33:06 +0300
>>> MailLists <lists at medesign.ro> wrote:
>>>
>>>> The recently acquired cash cow isn't working exactly as
>>>> expected/advertised. We still don't have a clue when/if the fundamental
>>>> (as in physics laws) design (we can't officially blame the cheap
>> Chinese
>>>> manufacturer) flaw will be fixed (manufacturer replaced), but as our
>>>> main customer, which is used to (literally) blow up tons of (others')
>>>> money, isn't very concerned (for now), and the profit margin is (still)
>>>> high enough to replace (no questions asked, for the time being) the
>>>> failed units of the other (civilian/commercial) customer(s).
>>>
>>> Sorry, but this is was not necessary.
>>> Not every company is evil and not every company just works for the
>>> short term bottom line.
>>>
>>> It is very normal that problems show up in series production which
>>> were not visible before in the prototypes or pre-series production.
>>> It's part of the very nature how volume production work. And no,
>>> you cannot always attriubute it to less care taken in the volume
>>> production than in the pre-series. Some flaws are only visible if
>>> you get enough produced and then it's still one in a couple hundred
>>> if not a one in a couple hundred thousand.
>>>
>>> Every product i was ever involved with had some flaws uncovered during
>>> series production. Even if the gratest care was taken. IMHO it does not
>>> matter whether the product has a shows suddenly a flaw or not, but how
>>> the manufacturer reacts to it. And as it seems Microsemi is replacing
>>> the failing units without causing trouble.
>>>
>>> Also, please be aware that fixing a flaw that only very few units show
>>> is not an easy thing. You cannot just build a prototype and be sure
>>> that the bug is gone. You have to first produce enough to have a
>> statistical
>>> significant sample size. This all takes time, weeks, months, or even
>> years.
>>>
>>>
>>> So, please refrain from spreading false rumors that anyone is ignoring
>> the
>>> issue when aparently the contrary is the case.
>>>
>>>
>>>                        Attila Kinali
>>>
>>> PS: Disclaimer: i neither work for or have any ties with Microsemi or
>>> Jacksonlabs.
>>>
>>> --
>>> I pity people who can't find laughter or at least some bit of amusement
>> in
>>> the little doings of the day. I believe I could find something ridiculous
>>> even in the saddest moment, if necessary. It has nothing to do with being
>>> superficial. It's a matter of joy in life.
>>>                        -- Sophie Scholl
>>> _______________________________________________
>>> 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.
>>
>>
>> ------------------------------
>>
>> Message: 3
>> Date: Fri, 25 Apr 2014 10:14:03 -0500
>> From: Didier Juges <shalimr9 at gmail.com>
>> To: Discussion of precise time and frequency measurement
>>          <time-nuts at febo.com>
>> Subject: Re: [time-nuts] How to accurately measure an oscillator's
>>          temperature.
>> Message-ID: <ff7e5bee-0a2b-4bd5-a400-f162cb057f5b at email.android.com>
>> Content-Type: text/plain; charset=UTF-8
>>
>> The best way is to place the temperature sensor near the part or parts
>> that are the most temperature sensitive. When dealing with something that
>> is already in an oven, that may not be so easy.
>>
>> Didier KO4BB
>>
>> On April 23, 2014 9:37:29 PM CDT, Chris Albertson <
>> albertson.chris at gmail.com> wrote:
>>> I have both an OCXO and an FE-5680 Rb oscillator and I'd like to track
>>> their temperatures.
>>>
>>> What is the best why to measure?   Maybe each has a different best
>>> method
>>>
>>> The OCXO is just a small steel can.  Is measuring the steel can
>>> temperature
>>> the best why to go.  Epoxy some kind of sensor to it?
>>>
>>> The Rb is mounded to a large heat sink and there is a fan.  I want to
>>> control the fan so as to keep the Rb temperature constant.
>>>
>>> In both cases I tried using TMP36 three terminal sensors and just got
>>> noise.  The reported temperature was up and down more than 2C.    The
>>> fan
>>> controller just chases noise.
>>>
>>> BTW the fan based temperature control is effective.  The FE5680 gets
>>> very
>>> warm in it's box but if I give the 12V fan even 8 volts the heat sink
>>> quickly cools.  I want to throttle the fan to keep the Rb at constant
>>> temperature but the temperature data I'm getting is not very good.
>>>
>>> The problem I think is that any sensor I have is on the outside of the
>>> oscillator and is effected by cooling air   What are others doing?
>>> What's
>>> the best kind of sensor.
>>>
>>> --
>>>
>>> Chris Albertson
>>> Redondo Beach, California
>>> _______________________________________________
>>> 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.
>>
>> --
>> Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other
>> things.
>>
>> ------------------------------
>>
>> Message: 4
>> Date: Fri, 25 Apr 2014 08:42:16 -0700
>> From: Chris Albertson <albertson.chris at gmail.com>
>> To: Discussion of precise time and frequency measurement
>>          <time-nuts at febo.com>
>> Subject: Re: [time-nuts] Low SNR GPS reception and cheap LNAs
>> Message-ID:
>>          <CABbxVHsgpzoeptP-GaY2sBuQ67k4WJF-B534XBAXbxA=
>> 0nEszA at mail.gmail.com>
>> Content-Type: text/plain; charset=UTF-8
>>
>> On Fri, Apr 25, 2014 at 6:28 AM, Attila Kinali <attila at kinali.ch> wrote:
>>
>>> Hi,
>>>
>>> I recently bought a bladeRF[1] to experiment a bit with GPS decoding.
>>>
>>> I tried to get GNSS-SDR[2] which seems quite good, but has its flaws.
>>> One of the things was that i cannot seem to get a fix in my environment.
>>> One of the problems seems that my antenna position is far from optimal.
>>> Aparently, GNSS-SDR uses only a very rudimentary acquisition technique
>>> (at least so i have been told). Now i wonder what techniques for low SNR
>>> acquisition are around. Would someone be so kind and give me some key
>>> words to google for?
>>>
>>> I also am looking to add an LNA to my reception chain, which is a
>>> mix of a 50R antenna with 75R Coaxcable (sat coax stuff is just a lot
>>> cheaper :-). Has anyone a recomendation for a good LNA that can be used
>>> in a flying construction (soldering onto two back-to-back glued
>>> connectors)?
>>> Ie it shouldnt be a QFN or BGA. DFN works but i'd rather have something
>>> with pins, like SC-70/SOT-323 or similar/larger.
>>>
>>
>> You best bet is to change out the antenna.  You can buy them with a higher
>> built-in gain up to about 40dB.   My understanding is that designing a GOOD
>> LNA is not so easy as little things like the exact layout of the PCB and
>> how the PCB transitions to connectors matters a lot.  But you can buy these
>> ready made for cheap.  I've seen complete LNAs in an enclosure with
>> connectors at good prices on eBay.    The user manuals I have say using 75R
>> cables with compression type F connects is OK.    I doubt the cheaper type
>> f-connectors would work well.
>>
>> I have a good high quality Tremble in-line amplifier with N-connector and
>> the ability to pass DC.   In my experiment I place the antenna indoor and
>> use amplifier and then outdoors with no amplifier.  I get MUCH better
>> results with my 26dB gain antenna on the roof and 25 feet of cable than
>> with indoor amplified antenna with short cable.      My un-scientific
>> conclusion was that amplified noise is still noise.
>>
>>>
>>>
>>>                          Attila Kinali
>>>
>>>
>>> [1] www.nuand.com/bladeRF
>>> [2] www.gnss-sdr.org
>>>
>>> --
>>> The trouble with you, Shev, is you don't say anything until you've saved
>>> up a whole truckload of damned heavy brick arguments and then you dump
>>> them all out and never look at the bleeding body mangled beneath the heap
>>>                  -- Tirin, The Dispossessed, U. Le Guin
>>> _______________________________________________
>>> 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.
>>>
>>
>>
>>
>> --
>>
>> Chris Albertson
>> Redondo Beach, California
>>
>>
>> ------------------------------
>>
>> _______________________________________________
>> time-nuts mailing list
>> time-nuts at febo.com
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>
>> End of time-nuts Digest, Vol 117, Issue 94
>> ******************************************
>>
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