[time-nuts] Rb vs.Crystal OCXO

Shane Kirkbride shane.kirkbride at gmail.com
Fri Apr 25 16:12:53 UTC 2014


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
>
>
> ------------------------------
>
> _______________________________________________
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> End of time-nuts Digest, Vol 117, Issue 94
> ******************************************
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