date:20121216

Hi

By far the most common way to test and certify OCXO's is in moving air. It's 
rare to see one get in trouble from to much ventilation. The more common 
problem is thermal runaway due to inadequate ventilation. 

Bob
 
On Dec 16, 2012, at 7:57 AM, Volker Esper ail...@t-online.de wrote:

 
 Steward,
 
 What is the intended and what is the actual supply voltage? Which current is 
 the unit consuming?
 When we know that, we can compare the power consumption with our units. If it 
 is in the same range, it should - with a little luck - be working properly.
 
 My two units are intended to be supplied by 19.5 to 30 V. I use 24 V and the 
 Z3805s draw 0.9 A each. If I increase voltage the current decreases (typical 
 for the switching supplies inside the Z3805).
 
 I don't cool the units, they just lie on an old electronics magazine (for not 
 to scratch the case of my signal generator, lying below the magazine), so 
 they can freely convect their heat.
 
 Cheers
 
 Volker
 
 
 
 Am 12.12.2012 01:21, schrieb Stewart Cobb:
 This may be a newbie question, but I'm a newbie, so:
 
 Do the HP telecom GPSDOs (Z38xx) require external airflow for cooling?
 They don't have built-in fans, but they sorta look like they depend on a
 rack-level cooling fan, which a telecom rack would almost certainly have.
 
 I ask because I bought a Z3816 awhile back which worked for about a week
 and then failed. I traced the failure to an internal power supply brick,
 which had a big finned heat-sink attached but nevertheless smelled
 overheated and was shorted internally.
 
 I never found a replacement power brick, and I don't have time to mess with
 it right now, so I recently bought a Z3805A. It, too, looks like it's
 working, but it started to feel awfully warm after a few hours, so I
 unplugged it for now.
 
 It probably wouldn't take much of a fan to bring the internal temperature
 down close to ambient, and the fan could be powered easily enough from the
 supply rails. But that might create a temperature gradient where the
 designers didn't intend one. Or it might cause problems I don't even know
 about yet.
 
 At the moment, the Z3805A is in a fan-less 19-inch rack with a bunch of
 other equipment, in a lab environment. Should it have its own fan?
 
 Cheers!
 --Stu
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[time-nuts] Watch Crystals On ECN

2012-12-16 Thread M. Simon

This is a rehash with better organization and more links of my side of a 
discussion here.


http://www.ecnmag.com/blogs/2012/12/exploring-potential-watch-crystals


And for those who intend to comment on the mystery list the last line (not 
counting philosophy and contact info):

The above is in part a recap of my side of a discussion on a list which prefers 
you to find it on your own.

Simon

Engineering is the art of making what you want from what you can get at a 
profit.
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Re: [time-nuts] Cell timing error

2012-12-16 Thread Graham / KE9H


On 12/15/2012 9:38 PM, Hal Murray wrote:

GSM cell sites in the US have GPS because it is required to support E911
positioning.  I'm not sure if it is used for anything other than this, but
it doesn't have to be.

So it's cheaper to install and maintain GPS rather than make one measurement
and tell the setup where it is?




No.

In addition to knowing where the GSM cell site is, you time stamp the 
time of arrival of a
specific feature in the cellphone signalling system.  If the cellphone 
is heard by three
(or more) cell sites, then you can calculate the location of the 
cellphone within the

cell site using the time-of-arrival and speed-of-light calculations.

The CDMA systems inherently depend on knowing time to sub microseconds 
in order
to function.  You can extract similar information from the signalling 
systems in CDMA.


Newer cellphones have a GPS receiver front end inside the phone, which 
allows greater
accuracy than the time of arrival systems.  Many times, cellular signals 
bounce off
of things between the handset and the base station, introducing a path 
length change and
therefore a time-of-flight delay in the signal which causes errors in 
the time of arrival

calculations.

--- Graham / KE9H

==

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Re: [time-nuts] Z3805A cooling requirements?

2012-12-16 Thread Volker Esper



Indeed? I didn't expect that. There are people who say, that the control 
loop of OCXOs is optimized for still air and no additional cooling at all.


Said told us, that...

...a fan is about the worst thing you can do for your Z3805 it will
significantly worsen the stability of the output frequency...

Since the main task of the OCXO-oven is to stabilize the internal 
temperature, I can't imagine, that it get's into trouble when not 
externally cooled!?


If I'd ventilate the air around the OCXO case the heater had to work 
more and the power dissipation would be greater.


Am I wrong with taht?

Volker



Am 16.12.2012 15:35, schrieb Bob Camp:

Hi

By far the most common way to test and certify OCXO's is in moving air. It's 
rare to see one get in trouble from to much ventilation. The more common 
problem is thermal runaway due to inadequate ventilation.

Bob

On Dec 16, 2012, at 7:57 AM, Volker Esperail...@t-online.de  wrote:



Steward,

What is the intended and what is the actual supply voltage? Which current is 
the unit consuming?
When we know that, we can compare the power consumption with our units. If it 
is in the same range, it should - with a little luck - be working properly.

My two units are intended to be supplied by 19.5 to 30 V. I use 24 V and the 
Z3805s draw 0.9 A each. If I increase voltage the current decreases (typical 
for the switching supplies inside the Z3805).

I don't cool the units, they just lie on an old electronics magazine (for not 
to scratch the case of my signal generator, lying below the magazine), so they 
can freely convect their heat.

Cheers

Volker



Am 12.12.2012 01:21, schrieb Stewart Cobb:

This may be a newbie question, but I'm a newbie, so:

Do the HP telecom GPSDOs (Z38xx) require external airflow for cooling?
They don't have built-in fans, but they sorta look like they depend on a
rack-level cooling fan, which a telecom rack would almost certainly have.

I ask because I bought a Z3816 awhile back which worked for about a week
and then failed. I traced the failure to an internal power supply brick,
which had a big finned heat-sink attached but nevertheless smelled
overheated and was shorted internally.

I never found a replacement power brick, and I don't have time to mess with
it right now, so I recently bought a Z3805A. It, too, looks like it's
working, but it started to feel awfully warm after a few hours, so I
unplugged it for now.

It probably wouldn't take much of a fan to bring the internal temperature
down close to ambient, and the fan could be powered easily enough from the
supply rails. But that might create a temperature gradient where the
designers didn't intend one. Or it might cause problems I don't even know
about yet.

At the moment, the Z3805A is in a fan-less 19-inch rack with a bunch of
other equipment, in a lab environment. Should it have its own fan?

Cheers!
--Stu
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Re: [time-nuts] Cell timing error


On 12/16/2012 05:40 PM, Graham / KE9H wrote:

In addition to knowing where the GSM cell site is, you time stamp the
time of arrival of a
specific feature in the cellphone signalling system. If the cellphone is
heard by three
(or more) cell sites, then you can calculate the location of the
cellphone within the
cell site using the time-of-arrival and speed-of-light calculations.


Since GSM is a TDM system, the arrival time of the TDM slot is the 
typical feature to measure. The active base station already does this, 
and send trimming values to steer the hand-set to stay within it's 
time-slot. This way you have a range measure, but it isn't enough for 
triangulation, so you would need to have another station measuring it 
too, but GSM will not usually do that, so you need to have a secondary 
receiver, tuned to the neighbour frequency in that direction.



The CDMA systems inherently depend on knowing time to sub microseconds
in order
to function. You can extract similar information from the signalling
systems in CDMA.


You inherently have the same knowledge in GSM, it's just that you don't 
care about absolute time, but relative timing between the hand-set and 
the base station is being measured and steered.


GSM stations being phase-aligned have better hand-over properties, and 
thus releases the channel in the cell the phone is leaving quicker, and 
thus increases the capacity... and allows new customers in and thus more 
money. So, well-timed base-stations is good for GSM too.


Cheers,
Magnus

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Re: [time-nuts] Z3805A cooling requirements?

Hi Volker,

You are correct on that.

Bob is right in that thermal sensitivity is measured in a thermal chamber with 
constant airflow at a very constant rate and temperature. While this works, it 
is also somewhat unrealistic because who is going to set up a thermal chamber 
for their ocxo in the field?

Because of that many companies put airflow shields on top of the ocxo in the 
test chamber to simulate more real life conditions where massive airflow is not 
happening, and self heating needs to be taken into consideration.

Moving-air skews the operating power of the ocxo as it removes heat from the 
ocxo. Thus a manufacturer could claim +75C max operating temp inside a test 
chamber, but if you try to operate in still air at 75C in a small enclosure 
your ocxo would overheat quickly due to the internal power consumption adding 
to the ambient temperature. Thus the test chamber actually works to cool the 
ocxo by removing excess heat and keeping its case at 75C no matter how much 
power is consumed inside the ocxo.

As an example of this consider that a typical DOCXO runs at 55C case temp in 
still air with 22C ambient. Now say that Docxo has 1E-010 per degree C thermal 
sensitivity (not a great docxo.. But thats actually better than the spec of the 
ocxo used on the Mini-T: that one is 10ppb from 0C to 60 C as far as I know)

What happens when I turn on a strong fan right next to the Docxo? The fan will 
throw ambient air at the same 22C temperature at the unit, and immediately 
start cooling off the 55C case of the ocxo due to the temp difference between 
the ocxo case and ambient air.

The result? If the fan can cool off the Docxo to say 30C, we have had a massive 
25C temperature change shock on the docxo without a single C temp change in 
ambient air!

Now 25C * 1E-010/C = 2.5E-09 change in frequency which gives a 2.5ns/s drift 
rate just because the fan switched on!

Typical single oven ocxos will have about 1ppb per C sensitivity, so the above 
example would result in 25ns/s drift just because the fan came on. Thats really 
bad for Gpsdo type performance expectations, and will certainly ruin your ADEV 
performance which us time-nuts expect to be around 1E-012 not 2E-08 for a good 
gpsdo :)

Hope this shows why a fan on an ocxo is not a good idea.

Bye,
Said

 





On Dec 16, 2012, at 9:47, Volker Esper ail...@t-online.de wrote:

 
 Indeed? I didn't expect that. There are people who say, that the control loop 
 of OCXOs is optimized for still air and no additional cooling at all.
 
 Said told us, that...
 
 ...a fan is about the worst thing you can do for your Z3805 it will
 significantly worsen the stability of the output frequency...
 
 Since the main task of the OCXO-oven is to stabilize the internal 
 temperature, I can't imagine, that it get's into trouble when not externally 
 cooled!?
 
 If I'd ventilate the air around the OCXO case the heater had to work more and 
 the power dissipation would be greater.
 
 Am I wrong with taht?
 
 Volker
 
 
 
 Am 16.12.2012 15:35, schrieb Bob Camp:
 Hi
 
 By far the most common way to test and certify OCXO's is in moving air. It's 
 rare to see one get in trouble from to much ventilation. The more common 
 problem is thermal runaway due to inadequate ventilation.
 
 Bob
 
 On Dec 16, 2012, at 7:57 AM, Volker Esperail...@t-online.de  wrote:
 
 
 Steward,
 
 What is the intended and what is the actual supply voltage? Which current 
 is the unit consuming?
 When we know that, we can compare the power consumption with our units. If 
 it is in the same range, it should - with a little luck - be working 
 properly.
 
 My two units are intended to be supplied by 19.5 to 30 V. I use 24 V and 
 the Z3805s draw 0.9 A each. If I increase voltage the current decreases 
 (typical for the switching supplies inside the Z3805).
 
 I don't cool the units, they just lie on an old electronics magazine (for 
 not to scratch the case of my signal generator, lying below the magazine), 
 so they can freely convect their heat.
 
 Cheers
 
 Volker
 
 
 
 Am 12.12.2012 01:21, schrieb Stewart Cobb:
 This may be a newbie question, but I'm a newbie, so:
 
 Do the HP telecom GPSDOs (Z38xx) require external airflow for cooling?
 They don't have built-in fans, but they sorta look like they depend on a
 rack-level cooling fan, which a telecom rack would almost certainly have.
 
 I ask because I bought a Z3816 awhile back which worked for about a week
 and then failed. I traced the failure to an internal power supply brick,
 which had a big finned heat-sink attached but nevertheless smelled
 overheated and was shorted internally.
 
 I never found a replacement power brick, and I don't have time to mess with
 it right now, so I recently bought a Z3805A. It, too, looks like it's
 working, but it started to feel awfully warm after a few hours, so I
 unplugged it for now.
 
 It probably wouldn't take much of a fan to bring the internal temperature
 down close to ambient, and the fan could

Re: [time-nuts] Z3805A cooling requirements?

Hi

Ok where to start.

Some typical numbers:

A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to 
+70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be 
specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb per 
degree. Yes, there are a number of variations, but those numbers are not at all 
crazy. eBay will happy cough up a lot of parts with those sort of numbers on 
them. 

---

Both devices will heat the crystal to a constant temperature when the ambient 
(however it's measured) is in the range of -30 to +70C. If it's below -30, 
there may not be enough oven power to heat the crystal. More likely there's not 
enough power to warm it up in the specified warmup time. If the ambient is 
above +70, even by a few degrees, the crystal can overheat. Exactly what 
temperature it starts to overheat is a function of several things, mainly the 
tolerances on cutting process of the crystal. When it does overheat, it's 
likely to move 10 to 20 ppb per degree for that first degree. That's *way* more 
than you would ever want to see.

It would be nice if control loops had no noise, and if the crystal heated and 
cooled at the same rate. In fact, you have enough heater power to run things up 
at a very high rate (you want to warm the thing up very quickly). The cooling 
rate at the hot end is not so fast (small delta T = low heat flow) .  A noise 
spike that gets the crystal too hot, will hang around for a while. You can have 
short term stability trouble before the oven is fully shut off.

Simply put - OCXO's don't play nice beyond their upper ambient spec. 

-

In most gear, there's a fan, and it runs all the time. It may speed up a bit 
when things get real hot, but that's about it. With a fan like that, when the 
ambient moves a degree or two, the inside of the box moves a degree or two. 
There is no catastrophe when the fan suddenly comes on. If anything most 
variable speed fan setups result in the innards of the box seeing less 
temperature change rather than more. Thermally, fans are a good idea. 



Now, taking those numbers (and a few assumptions, and the numbers from the 
previous post):

Let's say your gizmo does have a case that's 22C above ambient. Let's also say 
there is no fan. Let's also assume that there's something else in the box. It's 
pretty common for the stuff in a box to heat it up by 20C or more with no fan 
(The ambient inside the box is 20C above the outside air). If the gizmo is in 
the box, it's case is now 44C above the outside air. 

deep breath….

If the outside air is at 30C, your gizmo is at 74C. If it's an OCXO with a 70C 
upper end rating, it could be in trouble. The rest of the box is perfectly 
happy. It's designed with 70C rated parts and the spec on the box is 50C max.  

Yes, that's a lot of this and that. Yes there are some assumptions sprinkled 
here and there. Without assuming a few things there's not much way to get to a 
rational conclusion. Are OCXO's a bit strange thermally - yes of course they 
are. An eBay surplus rubidium is even stranger. Power transistors have issues 
as well. Stuff that has power associated with it needs some attention as part 
of the thermal design….

---

Are big / noisy / shaky / power hungry fans a good thing - of course not. They 
are simply the most common way to solve thermal problems in equipment. These 
days you can get fans that are less big/noisy/shaky than they once were. It's 
still better to not use them *if* you have all your thermal ducks in a row. 
That means you have the full specification on the OCXO (and likely a few other 
things). 

If we're talking about surplus gear or parts - you are not going to have a lot 
of information. The only reasonable assumption you can make is that the eBay 
OCXO is rated for moving air. Assuming you know the upper ambient of the OCXO, 
check it's actual case temperature. Keep it below the specified max ambient. 
Ideally, keep it 10 C or more below the rated upper ambient. The short term 
stability likely will be better ….

Bob 


On Dec 16, 2012, at 2:22 PM, Said Jackson saidj...@aol.com wrote:

 Hi Volker,
 
 You are correct on that.
 
 Bob is right in that thermal sensitivity is measured in a thermal chamber 
 with constant airflow at a very constant rate and temperature. While this 
 works, it is also somewhat unrealistic because who is going to set up a 
 thermal chamber for their ocxo in the field?
 
 Because of that many companies put airflow shields on top of the ocxo in the 
 test chamber to simulate more real life conditions where massive airflow is 
 not happening, and self heating needs to be taken into consideration.
 
 Moving-air skews the operating power of the ocxo as it removes heat from the 
 ocxo. Thus a manufacturer could claim +75C max operating temp inside a test 
 chamber, but if you try to operate in still air at

Re: [time-nuts] Z3805A cooling requirements?

Bob,

We agree that Ocxos get real bad real fast if overheated. Not a problem in the 
Z3805A box when run on a desk without clogging the vent holes, which is how 
this thread started (do I need a fan for my Z3805A...)

Your stability numbers are very optimistic. There are very few single oven 
Ocxos with 10ppb peak over 100C. Typical numbers are +/-2.5E-08 -see for 
example the MTI 230 series, or +/-5E-08 for the Morion MV103 series. Is it 
possible? Yes. Our Mini-JLT single oven has +/-5E-09 from -40C to +85C 
stability. But that uses an exceptional and quite expensive single oven Ocxo 
with SC cut crystal.

How about 0.3ppb over -30C to +70C? That's not standard by any means, very few 
vendors can do that. Heck even the CSAC doesn't even get close to that (its 
rated at +/-1ppb over that temp range). The best eurocan Docxo we offer has 
+/-0.2ppb over that range for a total of 0.4ppb. and it costs a huge amount of 
$$$. So which parts are you referring to here?

We have done extensive tests here on exactly this issue: how do real life Ocxos 
react to varying airflow. Any airflow causes turbulence, so even constant 
airflow varies in this sense. All I can say is not well at all. Tom Van Back 
has done some testing on our FireFly-1A GPSDO some years ago including tests 
with a fan, he may be willing to share the results of that test. The FF-1A has 
a spec of +/-25ppb over temp, so it's a typical SOCXO in our opinion.

Lastly, don't forget that it's not just the ocxo that's airflow sensitive, the 
DAC, filters, amp, and DAC reference all are thermally sensitive and will be 
affected by airflow as well.

The answer to this discussion would be easy to get: put a fan inside the Z3805A 
and check its adev with and without the fan. I am willing to bet a GPSTCXO eval 
kit that all else being the same the fan version will have higher noise (ADEV 
an PN). If the 58503A or Z3815A desktop versions needed a fan, I am sure HP 
would have designed one into it..

Bye,
Said



Sent from my iPad

On Dec 16, 2012, at 3:38 PM, Bob Camp li...@rtty.us wrote:

 Hi
 
 Ok where to start.
 
 Some typical numbers:
 
 A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to 
 +70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be 
 specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb per 
 degree. Yes, there are a number of variations, but those numbers are not at 
 all crazy. eBay will happy cough up a lot of parts with those sort of numbers 
 on them. 
 
 ---
 
 Both devices will heat the crystal to a constant temperature when the ambient 
 (however it's measured) is in the range of -30 to +70C. If it's below -30, 
 there may not be enough oven power to heat the crystal. More likely there's 
 not enough power to warm it up in the specified warmup time. If the ambient 
 is above +70, even by a few degrees, the crystal can overheat. Exactly what 
 temperature it starts to overheat is a function of several things, mainly the 
 tolerances on cutting process of the crystal. When it does overheat, it's 
 likely to move 10 to 20 ppb per degree for that first degree. That's *way* 
 more than you would ever want to see.
 
 It would be nice if control loops had no noise, and if the crystal heated and 
 cooled at the same rate. In fact, you have enough heater power to run things 
 up at a very high rate (you want to warm the thing up very quickly). The 
 cooling rate at the hot end is not so fast (small delta T = low heat flow) 
 .  A noise spike that gets the crystal too hot, will hang around for a while. 
 You can have short term stability trouble before the oven is fully shut off.
 
 Simply put - OCXO's don't play nice beyond their upper ambient spec. 
 
 -
 
 In most gear, there's a fan, and it runs all the time. It may speed up a bit 
 when things get real hot, but that's about it. With a fan like that, when the 
 ambient moves a degree or two, the inside of the box moves a degree or two. 
 There is no catastrophe when the fan suddenly comes on. If anything most 
 variable speed fan setups result in the innards of the box seeing less 
 temperature change rather than more. Thermally, fans are a good idea. 
 
 
 
 Now, taking those numbers (and a few assumptions, and the numbers from the 
 previous post):
 
 Let's say your gizmo does have a case that's 22C above ambient. Let's also 
 say there is no fan. Let's also assume that there's something else in the 
 box. It's pretty common for the stuff in a box to heat it up by 20C or more 
 with no fan (The ambient inside the box is 20C above the outside air). If 
 the gizmo is in the box, it's case is now 44C above the outside air. 
 
 deep breath….
 
 If the outside air is at 30C, your gizmo is at 74C. If it's an OCXO with a 
 70C upper end rating, it could be in trouble. The rest of the box is 
 perfectly happy. It's designed with 70C rated parts and the spec on

Re: [time-nuts] Z3805A cooling requirements?

One item I forgot to mention:

One of the most airflow sensitive parts inside a GPSDO is the tcxo used on the 
GPS receiver. Some GPS don't even use a tcxo, just an XO. They shall remain 
unnamed.

Just lightly blowing on an M12+ GPS will make it lose lock immediatly.

This is easy to try for time nuts, and to verify the sensitivity to airflow.

Bye,
Said

Sent from my iPad

On Dec 16, 2012, at 4:37 PM, Said Jackson saidj...@aol.com wrote:

 Bob,
 
 We agree that Ocxos get real bad real fast if overheated. Not a problem in 
 the Z3805A box when run on a desk without clogging the vent holes, which is 
 how this thread started (do I need a fan for my Z3805A...)
 
 Your stability numbers are very optimistic. There are very few single oven 
 Ocxos with 10ppb peak over 100C. Typical numbers are +/-2.5E-08 -see for 
 example the MTI 230 series, or +/-5E-08 for the Morion MV103 series. Is it 
 possible? Yes. Our Mini-JLT single oven has +/-5E-09 from -40C to +85C 
 stability. But that uses an exceptional and quite expensive single oven Ocxo 
 with SC cut crystal.
 
 How about 0.3ppb over -30C to +70C? That's not standard by any means, very 
 few vendors can do that. Heck even the CSAC doesn't even get close to that 
 (its rated at +/-1ppb over that temp range). The best eurocan Docxo we offer 
 has +/-0.2ppb over that range for a total of 0.4ppb. and it costs a huge 
 amount of $$$. So which parts are you referring to here?
 
 We have done extensive tests here on exactly this issue: how do real life 
 Ocxos react to varying airflow. Any airflow causes turbulence, so even 
 constant airflow varies in this sense. All I can say is not well at all. 
 Tom Van Back has done some testing on our FireFly-1A GPSDO some years ago 
 including tests with a fan, he may be willing to share the results of that 
 test. The FF-1A has a spec of +/-25ppb over temp, so it's a typical SOCXO 
 in our opinion.
 
 Lastly, don't forget that it's not just the ocxo that's airflow sensitive, 
 the DAC, filters, amp, and DAC reference all are thermally sensitive and will 
 be affected by airflow as well.
 
 The answer to this discussion would be easy to get: put a fan inside the 
 Z3805A and check its adev with and without the fan. I am willing to bet a 
 GPSTCXO eval kit that all else being the same the fan version will have 
 higher noise (ADEV an PN). If the 58503A or Z3815A desktop versions needed a 
 fan, I am sure HP would have designed one into it..
 
 Bye,
 Said
 
 
 
 Sent from my iPad
 
 On Dec 16, 2012, at 3:38 PM, Bob Camp li...@rtty.us wrote:
 
 Hi
 
 Ok where to start.
 
 Some typical numbers:
 
 A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to 
 +70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be 
 specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb per 
 degree. Yes, there are a number of variations, but those numbers are not at 
 all crazy. eBay will happy cough up a lot of parts with those sort of 
 numbers on them. 
 
 ---
 
 Both devices will heat the crystal to a constant temperature when the 
 ambient (however it's measured) is in the range of -30 to +70C. If it's 
 below -30, there may not be enough oven power to heat the crystal. More 
 likely there's not enough power to warm it up in the specified warmup time. 
 If the ambient is above +70, even by a few degrees, the crystal can 
 overheat. Exactly what temperature it starts to overheat is a function of 
 several things, mainly the tolerances on cutting process of the crystal. 
 When it does overheat, it's likely to move 10 to 20 ppb per degree for that 
 first degree. That's *way* more than you would ever want to see.
 
 It would be nice if control loops had no noise, and if the crystal heated 
 and cooled at the same rate. In fact, you have enough heater power to run 
 things up at a very high rate (you want to warm the thing up very quickly). 
 The cooling rate at the hot end is not so fast (small delta T = low heat 
 flow) .  A noise spike that gets the crystal too hot, will hang around for a 
 while. You can have short term stability trouble before the oven is fully 
 shut off.
 
 Simply put - OCXO's don't play nice beyond their upper ambient spec. 
 
 -
 
 In most gear, there's a fan, and it runs all the time. It may speed up a bit 
 when things get real hot, but that's about it. With a fan like that, when 
 the ambient moves a degree or two, the inside of the box moves a degree or 
 two. There is no catastrophe when the fan suddenly comes on. If anything 
 most variable speed fan setups result in the innards of the box seeing less 
 temperature change rather than more. Thermally, fans are a good idea. 
 
 
 
 Now, taking those numbers (and a few assumptions, and the numbers from the 
 previous post):
 
 Let's say your gizmo does have a case that's 22C above ambient. Let's also 
 say there is no fan. Let's also assume

Re: [time-nuts] Z3805A cooling requirements?

Hi

When you blow on a TCXO you are setting up variable airflow. A fan produces a 
constant airflow. A variable flow gives you a variable temperature. A constant 
flow keeps things pretty uniform. 

Environnemental chambers have pretty massive airflow. TCXO's and OCXO's do 
quite well inside them.

Bob

On Dec 16, 2012, at 8:16 PM, Said Jackson saidj...@aol.com wrote:

 One item I forgot to mention:
 
 One of the most airflow sensitive parts inside a GPSDO is the tcxo used on 
 the GPS receiver. Some GPS don't even use a tcxo, just an XO. They shall 
 remain unnamed.
 
 Just lightly blowing on an M12+ GPS will make it lose lock immediatly.
 
 This is easy to try for time nuts, and to verify the sensitivity to airflow.
 
 Bye,
 Said
 
 Sent from my iPad
 
 On Dec 16, 2012, at 4:37 PM, Said Jackson saidj...@aol.com wrote:
 
 Bob,
 
 We agree that Ocxos get real bad real fast if overheated. Not a problem in 
 the Z3805A box when run on a desk without clogging the vent holes, which is 
 how this thread started (do I need a fan for my Z3805A...)
 
 Your stability numbers are very optimistic. There are very few single oven 
 Ocxos with 10ppb peak over 100C. Typical numbers are +/-2.5E-08 -see for 
 example the MTI 230 series, or +/-5E-08 for the Morion MV103 series. Is it 
 possible? Yes. Our Mini-JLT single oven has +/-5E-09 from -40C to +85C 
 stability. But that uses an exceptional and quite expensive single oven Ocxo 
 with SC cut crystal.
 
 How about 0.3ppb over -30C to +70C? That's not standard by any means, very 
 few vendors can do that. Heck even the CSAC doesn't even get close to that 
 (its rated at +/-1ppb over that temp range). The best eurocan Docxo we offer 
 has +/-0.2ppb over that range for a total of 0.4ppb. and it costs a huge 
 amount of $$$. So which parts are you referring to here?
 
 We have done extensive tests here on exactly this issue: how do real life 
 Ocxos react to varying airflow. Any airflow causes turbulence, so even 
 constant airflow varies in this sense. All I can say is not well at all. 
 Tom Van Back has done some testing on our FireFly-1A GPSDO some years ago 
 including tests with a fan, he may be willing to share the results of that 
 test. The FF-1A has a spec of +/-25ppb over temp, so it's a typical SOCXO 
 in our opinion.
 
 Lastly, don't forget that it's not just the ocxo that's airflow sensitive, 
 the DAC, filters, amp, and DAC reference all are thermally sensitive and 
 will be affected by airflow as well.
 
 The answer to this discussion would be easy to get: put a fan inside the 
 Z3805A and check its adev with and without the fan. I am willing to bet a 
 GPSTCXO eval kit that all else being the same the fan version will have 
 higher noise (ADEV an PN). If the 58503A or Z3815A desktop versions needed a 
 fan, I am sure HP would have designed one into it..
 
 Bye,
 Said
 
 
 
 Sent from my iPad
 
 On Dec 16, 2012, at 3:38 PM, Bob Camp li...@rtty.us wrote:
 
 Hi
 
 Ok where to start.
 
 Some typical numbers:
 
 A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to 
 +70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be 
 specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb 
 per degree. Yes, there are a number of variations, but those numbers are 
 not at all crazy. eBay will happy cough up a lot of parts with those sort 
 of numbers on them. 
 
 ---
 
 Both devices will heat the crystal to a constant temperature when the 
 ambient (however it's measured) is in the range of -30 to +70C. If it's 
 below -30, there may not be enough oven power to heat the crystal. More 
 likely there's not enough power to warm it up in the specified warmup time. 
 If the ambient is above +70, even by a few degrees, the crystal can 
 overheat. Exactly what temperature it starts to overheat is a function of 
 several things, mainly the tolerances on cutting process of the crystal. 
 When it does overheat, it's likely to move 10 to 20 ppb per degree for that 
 first degree. That's *way* more than you would ever want to see.
 
 It would be nice if control loops had no noise, and if the crystal heated 
 and cooled at the same rate. In fact, you have enough heater power to run 
 things up at a very high rate (you want to warm the thing up very quickly). 
 The cooling rate at the hot end is not so fast (small delta T = low heat 
 flow) .  A noise spike that gets the crystal too hot, will hang around for 
 a while. You can have short term stability trouble before the oven is fully 
 shut off.
 
 Simply put - OCXO's don't play nice beyond their upper ambient spec. 
 
 -
 
 In most gear, there's a fan, and it runs all the time. It may speed up a 
 bit when things get real hot, but that's about it. With a fan like that, 
 when the ambient moves a degree or two, the inside of the box moves a 
 degree or two. There is no catastrophe when the fan suddenly comes on. If 
 anything most

Re: [time-nuts] Z3805A cooling requirements?


Said,

On 12/17/2012 02:16 AM, Said Jackson wrote:

One item I forgot to mention:

One of the most airflow sensitive parts inside a GPSDO is the tcxo used on the 
GPS receiver. Some GPS don't even use a tcxo, just an XO. They shall remain 
unnamed.

Just lightly blowing on an M12+ GPS will make it lose lock immediatly.

This is easy to try for time nuts, and to verify the sensitivity to airflow.

Bye,
Said


This comes as no surprise. I'm happy to learn about the details of your 
findings on the off-list form.


It does bring up the point that the GPS receivers clock should either be 
locked up or replaced with a stabler clock, preferably OCXO or derivate 
there off.


Maybe time to do a small hack for illustratory purposes?

Cheers,
Magnus

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Re: [time-nuts] Z3805A cooling requirements?

Well here's a few examples:

HP10811 is a single oven. It's spec'd at 4 ppb over -55 to +71C. It's certainly
a common eBay item. It's also what's in a 3805A.
http://www.hparchive.com/Manuals/HP-10811AB-Manual.pdf on page 3

The Morion DOCXO's on eBay are available at 0.2 ppb p-p -20 to +70C. (not
quite -30 but close)
http://www.ebay.com/itm/Morion-Double-oven-ultra-precision-OCXO-MV89A-/180791401266?pt=LH_DefaultDomain_0hash=item2a1801db32

http://morion.com.ru/catalog_pdf/MV89-OCXO.pdf

there are other examples.

Bob

On Dec 16, 2012, at 7:37 PM, Said Jackson saidj...@aol.com wrote:

Bob,

We agree that Ocxos get real bad real fast if overheated. Not a problem in
the Z3805A box when run on a desk without clogging the vent holes, which is
how this thread started (do I need a fan for my Z3805A...)

Your stability numbers are very optimistic. There are very few single oven
Ocxos with 10ppb peak over 100C. Typical numbers are +/-2.5E-08 -see for
example the MTI 230 series, or +/-5E-08 for the Morion MV103 series. Is it
possible? Yes. Our Mini-JLT single oven has +/-5E-09 from -40C to +85C
stability. But that uses an exceptional and quite expensive single oven Ocxo
with SC cut crystal.

How about 0.3ppb over -30C to +70C? That's not standard by any means, very
few vendors can do that. Heck even the CSAC doesn't even get close to that
(its rated at +/-1ppb over that temp range). The best eurocan Docxo we offer
has +/-0.2ppb over that range for a total of 0.4ppb. and it costs a huge
amount of $$$. So which parts are you referring to here?

We have done extensive tests here on exactly this issue: how do real life
Ocxos react to varying airflow. Any airflow causes turbulence, so even
constant airflow varies in this sense. All I can say is not well at all.
Tom Van Back has done some testing on our FireFly-1A GPSDO some years ago
including tests with a fan, he may be willing to share the results of that
test. The FF-1A has a spec of +/-25ppb over temp, so it's a typical SOCXO
in our opinion.

Lastly, don't forget that it's not just the ocxo that's airflow sensitive,
the DAC, filters, amp, and DAC reference all are thermally sensitive and will
be affected by airflow as well.

The answer to this discussion would be easy to get: put a fan inside the
Z3805A and check its adev with and without the fan. I am willing to bet a
GPSTCXO eval kit that all else being the same the fan version will have
higher noise (ADEV an PN). If the 58503A or Z3815A desktop versions needed a
fan, I am sure HP would have designed one into it..

Bye,
Said

Sent from my iPad

On Dec 16, 2012, at 3:38 PM, Bob Camp li...@rtty.us wrote:

Ok where to start.

Some typical numbers:

A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to
+70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be
specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb per
degree. Yes, there are a number of variations, but those numbers are not at
all crazy. eBay will happy cough up a lot of parts with those sort of
numbers on them.

---

Both devices will heat the crystal to a constant temperature when the
ambient (however it's measured) is in the range of -30 to +70C. If it's
below -30, there may not be enough oven power to heat the crystal. More
likely there's not enough power to warm it up in the specified warmup time.
If the ambient is above +70, even by a few degrees, the crystal can
overheat. Exactly what temperature it starts to overheat is a function of
several things, mainly the tolerances on cutting process of the crystal.
When it does overheat, it's likely to move 10 to 20 ppb per degree for that
first degree. That's *way* more than you would ever want to see.

It would be nice if control loops had no noise, and if the crystal heated
and cooled at the same rate. In fact, you have enough heater power to run
things up at a very high rate (you want to warm the thing up very quickly).
The cooling rate at the hot end is not so fast (small delta T = low heat
flow) . A noise spike that gets the crystal too hot, will hang around for a
while. You can have short term stability trouble before the oven is fully
shut off.

Simply put - OCXO's don't play nice beyond their upper ambient spec.

In most gear, there's a fan, and it runs all the time. It may speed up a bit
when things get real hot, but that's about it. With a fan like that, when
the ambient moves a degree or two, the inside of the box moves a degree or
two. There is no catastrophe when the fan suddenly comes on. If anything
most variable speed fan setups result in the innards of the box seeing less
temperature change rather than more. Thermally, fans are a good idea.

Now, taking those numbers (and a few assumptions,

Re: [time-nuts] Z3805A cooling requirements?


On 12/17/2012 02:21 AM, Bob Camp wrote:

Hi

When you blow on a TCXO you are setting up variable airflow. A fan produces a 
constant airflow. A variable flow gives you a variable temperature. A constant 
flow keeps things pretty uniform.

Environnemental chambers have pretty massive airflow. TCXO's and OCXO's do 
quite well inside them.


The trouble with airflows over a TCXO or OCXO compared to still air, is 
that you provide a better connectivity to the ambient air and it's 
variations. Hence, I get to monitor the AC in the building or testlab 
that way. Just tossing very mild isolation and it is almost quiet in 
comparison. A good quality environmental chamber doesn't have drastic 
puffs of heat-up, where as lesser onces do that. When testing TCXOs I 
learned more about the environment chamber in use than on the TCXO itself...


Again, your mileage WILL vary.

Oh, I do know some folks that are looking into the effect of turbulence 
of forced air on crystal noise. I could find some flaws in their line 
of reasoning.


Cheers,
Magnus

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and follow the instructions there.

Re: [time-nuts] Z3805A cooling requirements?

Hi

The gotcha here is that an un-cooled piece of gear will heat up and cool down 
as it's work load changes.  There is no magic bullet that keeps the 
temperature constant with zero airflow in a normal design. Yes, I'm old enough 
to remember oil cooled computers. Still no constant temperature and you have 
turbulence.  

Bob



On Dec 16, 2012, at 8:40 PM, Magnus Danielson mag...@rubidium.dyndns.org 
wrote:

 On 12/17/2012 02:21 AM, Bob Camp wrote:
 Hi
 
 When you blow on a TCXO you are setting up variable airflow. A fan produces 
 a constant airflow. A variable flow gives you a variable temperature. A 
 constant flow keeps things pretty uniform.
 
 Environnemental chambers have pretty massive airflow. TCXO's and OCXO's do 
 quite well inside them.
 
 The trouble with airflows over a TCXO or OCXO compared to still air, is that 
 you provide a better connectivity to the ambient air and it's variations. 
 Hence, I get to monitor the AC in the building or testlab that way. Just 
 tossing very mild isolation and it is almost quiet in comparison. A good 
 quality environmental chamber doesn't have drastic puffs of heat-up, where 
 as lesser onces do that. When testing TCXOs I learned more about the 
 environment chamber in use than on the TCXO itself...
 
 Again, your mileage WILL vary.
 
 Oh, I do know some folks that are looking into the effect of turbulence of 
 forced air on crystal noise. I could find some flaws in their line of 
 reasoning.
 
 Cheers,
 Magnus
 
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
 and follow the instructions there.


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Re: [time-nuts] Z3805A cooling requirements?

2012-12-16 Thread shalimr9

One more thing the Thunderbolt is essentially immune from since there is no 
separate XO for the GPS receiver which runs from the OCXO.

Didier

Sent from my Droid Razr 4G LTE wireless tracker.



-Original Message-
From: Said Jackson saidj...@aol.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Cc: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Sun, 16 Dec 2012 7:16 PM
Subject: Re: [time-nuts] Z3805A cooling requirements?

One item I forgot to mention:

One of the most airflow sensitive parts inside a GPSDO is the tcxo used on the 
GPS receiver. Some GPS don't even use a tcxo, just an XO. They shall remain 
unnamed.

Just lightly blowing on an M12+ GPS will make it lose lock immediatly.

This is easy to try for time nuts, and to verify the sensitivity to airflow.

Bye,
Said

Sent from my iPad

On Dec 16, 2012, at 4:37 PM, Said Jackson saidj...@aol.com wrote:

 Bob,
 
 We agree that Ocxos get real bad real fast if overheated. Not a problem in 
 the Z3805A box when run on a desk without clogging the vent holes, which is 
 how this thread started (do I need a fan for my Z3805A...)
 
 Your stability numbers are very optimistic. There are very few single oven 
 Ocxos with 10ppb peak over 100C. Typical numbers are +/-2.5E-08 -see for 
 example the MTI 230 series, or +/-5E-08 for the Morion MV103 series. Is it 
 possible? Yes. Our Mini-JLT single oven has +/-5E-09 from -40C to +85C 
 stability. But that uses an exceptional and quite expensive single oven Ocxo 
 with SC cut crystal.
 
 How about 0.3ppb over -30C to +70C? That's not standard by any means, very 
 few vendors can do that. Heck even the CSAC doesn't even get close to that 
 (its rated at +/-1ppb over that temp range). The best eurocan Docxo we offer 
 has +/-0.2ppb over that range for a total of 0.4ppb. and it costs a huge 
 amount of $$$. So which parts are you referring to here?
 
 We have done extensive tests here on exactly this issue: how do real life 
 Ocxos react to varying airflow. Any airflow causes turbulence, so even 
 constant airflow varies in this sense. All I can say is not well at all. 
 Tom Van Back has done some testing on our FireFly-1A GPSDO some years ago 
 including tests with a fan, he may be willing to share the results of that 
 test. The FF-1A has a spec of +/-25ppb over temp, so it's a typical SOCXO 
 in our opinion.
 
 Lastly, don't forget that it's not just the ocxo that's airflow sensitive, 
 the DAC, filters, amp, and DAC reference all are thermally sensitive and will 
 be affected by airflow as well.
 
 The answer to this discussion would be easy to get: put a fan inside the 
 Z3805A and check its adev with and without the fan. I am willing to bet a 
 GPSTCXO eval kit that all else being the same the fan version will have 
 higher noise (ADEV an PN). If the 58503A or Z3815A desktop versions needed a 
 fan, I am sure HP would have designed one into it..
 
 Bye,
 Said
 
 
 
 Sent from my iPad
 
 On Dec 16, 2012, at 3:38 PM, Bob Camp li...@rtty.us wrote:
 
 Hi
 
 Ok where to start.
 
 Some typical numbers:
 
 A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to 
 +70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be 
 specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb per 
 degree. Yes, there are a number of variations, but those numbers are not at 
 all crazy. eBay will happy cough up a lot of parts with those sort of 
 numbers on them. 
 
 ---
 
 Both devices will heat the crystal to a constant temperature when the 
 ambient (however it's measured) is in the range of -30 to +70C. If it's 
 below -30, there may not be enough oven power to heat the crystal. More 
 likely there's not enough power to warm it up in the specified warmup time. 
 If the ambient is above +70, even by a few degrees, the crystal can 
 overheat. Exactly what temperature it starts to overheat is a function of 
 several things, mainly the tolerances on cutting process of the crystal. 
 When it does overheat, it's likely to move 10 to 20 ppb per degree for that 
 first degree. That's *way* more than you would ever want to see.
 
 It would be nice if control loops had no noise, and if the crystal heated 
 and cooled at the same rate. In fact, you have enough heater power to run 
 things up at a very high rate (you want to warm the thing up very quickly). 
 The cooling rate at the hot end is not so fast (small delta T = low heat 
 flow) .  A noise spike that gets the crystal too hot, will hang around for a 
 while. You can have short term stability trouble before the oven is fully 
 shut off.
 
 Simply put - OCXO's don't play nice beyond their upper ambient spec. 
 
 -
 
 In most gear, there's a fan, and it runs all the time. It may speed up a bit 
 when things get real hot, but that's about it. With a fan like that, when 
 the ambient moves a degree or two, the inside of

Re: [time-nuts] Z3805A cooling requirements?

2012-12-16 Thread shalimr9

Forced air will generally be turbulent, which means that the air speed and 
pressure at any point will follow a somewhat normal (or not) random 
distribution. That is not good for something that needs stable cooling. Air 
flow resulting from convection cooling on the other hand is usually laminar, 
which means it is much more stable.

Didier

Sent from my Droid Razr 4G LTE wireless tracker.



-Original Message-
From: Bob Camp li...@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Sun, 16 Dec 2012 7:47 PM
Subject: Re: [time-nuts] Z3805A cooling requirements?

Hi

The gotcha here is that an un-cooled piece of gear will heat up and cool down 
as it's work load changes.  There is no magic bullet that keeps the 
temperature constant with zero airflow in a normal design. Yes, I'm old enough 
to remember oil cooled computers. Still no constant temperature and you have 
turbulence.  

Bob



On Dec 16, 2012, at 8:40 PM, Magnus Danielson mag...@rubidium.dyndns.org 
wrote:

 On 12/17/2012 02:21 AM, Bob Camp wrote:
 Hi
 
 When you blow on a TCXO you are setting up variable airflow. A fan produces 
 a constant airflow. A variable flow gives you a variable temperature. A 
 constant flow keeps things pretty uniform.
 
 Environnemental chambers have pretty massive airflow. TCXO's and OCXO's do 
 quite well inside them.
 
 The trouble with airflows over a TCXO or OCXO compared to still air, is that 
 you provide a better connectivity to the ambient air and it's variations. 
 Hence, I get to monitor the AC in the building or testlab that way. Just 
 tossing very mild isolation and it is almost quiet in comparison. A good 
 quality environmental chamber doesn't have drastic puffs of heat-up, where 
 as lesser onces do that. When testing TCXOs I learned more about the 
 environment chamber in use than on the TCXO itself...
 
 Again, your mileage WILL vary.
 
 Oh, I do know some folks that are looking into the effect of turbulence of 
 forced air on crystal noise. I could find some flaws in their line of 
 reasoning.
 
 Cheers,
 Magnus
 
 ___
 time-nuts mailing list -- time-nuts@febo.com
 To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] Z3805A cooling requirements?

Hi

First order immune due to the OCXO. You still have the RF stuff hanging out 
there in what ever breeze comes along. The OCXO does indeed change a bit if you 
go from still air to a raging blast. Not as much as a TCXO, but there is a 
shift.

Bob

On Dec 16, 2012, at 8:56 PM, shali...@gmail.com wrote:

 One more thing the Thunderbolt is essentially immune from since there is no 
 separate XO for the GPS receiver which runs from the OCXO.
 
 Didier
 
 Sent from my Droid Razr 4G LTE wireless tracker.
 
 
 
 -Original Message-
 From: Said Jackson saidj...@aol.com
 To: Discussion of precise time and frequency measurement time-nuts@febo.com
 Cc: Discussion of precise time and frequency measurement time-nuts@febo.com
 Sent: Sun, 16 Dec 2012 7:16 PM
 Subject: Re: [time-nuts] Z3805A cooling requirements?
 
 One item I forgot to mention:
 
 One of the most airflow sensitive parts inside a GPSDO is the tcxo used on 
 the GPS receiver. Some GPS don't even use a tcxo, just an XO. They shall 
 remain unnamed.
 
 Just lightly blowing on an M12+ GPS will make it lose lock immediatly.
 
 This is easy to try for time nuts, and to verify the sensitivity to airflow.
 
 Bye,
 Said
 
 Sent from my iPad
 
 On Dec 16, 2012, at 4:37 PM, Said Jackson saidj...@aol.com wrote:
 
 Bob,
 
 We agree that Ocxos get real bad real fast if overheated. Not a problem in 
 the Z3805A box when run on a desk without clogging the vent holes, which is 
 how this thread started (do I need a fan for my Z3805A...)
 
 Your stability numbers are very optimistic. There are very few single oven 
 Ocxos with 10ppb peak over 100C. Typical numbers are +/-2.5E-08 -see for 
 example the MTI 230 series, or +/-5E-08 for the Morion MV103 series. Is it 
 possible? Yes. Our Mini-JLT single oven has +/-5E-09 from -40C to +85C 
 stability. But that uses an exceptional and quite expensive single oven Ocxo 
 with SC cut crystal.
 
 How about 0.3ppb over -30C to +70C? That's not standard by any means, very 
 few vendors can do that. Heck even the CSAC doesn't even get close to that 
 (its rated at +/-1ppb over that temp range). The best eurocan Docxo we offer 
 has +/-0.2ppb over that range for a total of 0.4ppb. and it costs a huge 
 amount of $$$. So which parts are you referring to here?
 
 We have done extensive tests here on exactly this issue: how do real life 
 Ocxos react to varying airflow. Any airflow causes turbulence, so even 
 constant airflow varies in this sense. All I can say is not well at all. 
 Tom Van Back has done some testing on our FireFly-1A GPSDO some years ago 
 including tests with a fan, he may be willing to share the results of that 
 test. The FF-1A has a spec of +/-25ppb over temp, so it's a typical SOCXO 
 in our opinion.
 
 Lastly, don't forget that it's not just the ocxo that's airflow sensitive, 
 the DAC, filters, amp, and DAC reference all are thermally sensitive and 
 will be affected by airflow as well.
 
 The answer to this discussion would be easy to get: put a fan inside the 
 Z3805A and check its adev with and without the fan. I am willing to bet a 
 GPSTCXO eval kit that all else being the same the fan version will have 
 higher noise (ADEV an PN). If the 58503A or Z3815A desktop versions needed a 
 fan, I am sure HP would have designed one into it..
 
 Bye,
 Said
 
 
 
 Sent from my iPad
 
 On Dec 16, 2012, at 3:38 PM, Bob Camp li...@rtty.us wrote:
 
 Hi
 
 Ok where to start.
 
 Some typical numbers:
 
 A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to 
 +70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be 
 specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb 
 per degree. Yes, there are a number of variations, but those numbers are 
 not at all crazy. eBay will happy cough up a lot of parts with those sort 
 of numbers on them. 
 
 ---
 
 Both devices will heat the crystal to a constant temperature when the 
 ambient (however it's measured) is in the range of -30 to +70C. If it's 
 below -30, there may not be enough oven power to heat the crystal. More 
 likely there's not enough power to warm it up in the specified warmup time. 
 If the ambient is above +70, even by a few degrees, the crystal can 
 overheat. Exactly what temperature it starts to overheat is a function of 
 several things, mainly the tolerances on cutting process of the crystal. 
 When it does overheat, it's likely to move 10 to 20 ppb per degree for that 
 first degree. That's *way* more than you would ever want to see.
 
 It would be nice if control loops had no noise, and if the crystal heated 
 and cooled at the same rate. In fact, you have enough heater power to run 
 things up at a very high rate (you want to warm the thing up very quickly). 
 The cooling rate at the hot end is not so fast (small delta T = low heat 
 flow) .  A noise spike that gets the crystal too hot, will hang around for 
 a while. You can have short term stability trouble

Re: [time-nuts] Z3805A cooling requirements?


On 12/17/2012 02:47 AM, Bob Camp wrote:

Hi

The gotcha here is that an un-cooled piece of gear will heat up and cool down as it's 
work load changes.  There is no magic bullet that keeps the temperature 
constant with zero airflow in a normal design. Yes, I'm old enough to remember oil cooled 
computers. Still no constant temperature and you have turbulence.


I agree that there is no silver bullet, but my point was that 
sometimes you kill one property when you apply a solution to another 
problem. I am very well aware of heating problems and cooling my 
components, as this is part of my real world. But rather than isolating 
the full box, I'm talking about the TCXO or OCXO. Just putting a small 
wind-shield over it changes things a lot at times.


Cheers,
Magnus

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Re: [time-nuts] Z3805A cooling requirements?

Hi

The sort of thermal randomness that turbulence is going to create at fan speeds 
isn't going to come through the thermal mass of an OCXO to any great degree.

Bob

On Dec 16, 2012, at 9:05 PM, shali...@gmail.com wrote:

 Forced air will generally be turbulent, which means that the air speed and 
 pressure at any point will follow a somewhat normal (or not) random 
 distribution. That is not good for something that needs stable cooling. Air 
 flow resulting from convection cooling on the other hand is usually laminar, 
 which means it is much more stable.
 
 Didier
 
 Sent from my Droid Razr 4G LTE wireless tracker.
 
 
 
 -Original Message-
 From: Bob Camp li...@rtty.us
 To: Discussion of precise time and frequency measurement time-nuts@febo.com
 Sent: Sun, 16 Dec 2012 7:47 PM
 Subject: Re: [time-nuts] Z3805A cooling requirements?
 
 Hi
 
 The gotcha here is that an un-cooled piece of gear will heat up and cool down 
 as it's work load changes.  There is no magic bullet that keeps the 
 temperature constant with zero airflow in a normal design. Yes, I'm old 
 enough to remember oil cooled computers. Still no constant temperature and 
 you have turbulence.  
 
 Bob
 
 
 
 On Dec 16, 2012, at 8:40 PM, Magnus Danielson mag...@rubidium.dyndns.org 
 wrote:
 
 On 12/17/2012 02:21 AM, Bob Camp wrote:
 Hi
 
 When you blow on a TCXO you are setting up variable airflow. A fan produces 
 a constant airflow. A variable flow gives you a variable temperature. A 
 constant flow keeps things pretty uniform.
 
 Environnemental chambers have pretty massive airflow. TCXO's and OCXO's do 
 quite well inside them.
 
 The trouble with airflows over a TCXO or OCXO compared to still air, is that 
 you provide a better connectivity to the ambient air and it's variations. 
 Hence, I get to monitor the AC in the building or testlab that way. Just 
 tossing very mild isolation and it is almost quiet in comparison. A good 
 quality environmental chamber doesn't have drastic puffs of heat-up, where 
 as lesser onces do that. When testing TCXOs I learned more about the 
 environment chamber in use than on the TCXO itself...
 
 Again, your mileage WILL vary.
 
 Oh, I do know some folks that are looking into the effect of turbulence of 
 forced air on crystal noise. I could find some flaws in their line of 
 reasoning.
 
 Cheers,
 Magnus
 
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Re: [time-nuts] Z3805A cooling requirements?

Hi Bob,

Herein lies the problem. The MV89 you linked to on eBay is a Dash-A part, so
the lowest stability one.. Hard to get the more stable ones.

Also, I am not looking for a single unit from EBay, I'm interested in sustained
production/reasonable pricing. Morion is very hard to deal with, and very
difficult to buy from. The 10811 are also very hard to get new, and not cheap.

So I guess it depends on the application -hobby or production.

Nonetheless, even the ovens you mention inside a GPSDO will have a phase drift
with changing airflow, and one interesting item to note is that no ocxo vendor
actually specifies stability over varying airflow.

Bye,
Said

Sent from my iPad

On Dec 16, 2012, at 5:39 PM, Bob Camp li...@rtty.us wrote:

Well here's a few examples:

HP10811 is a single oven. It's spec'd at 4 ppb over -55 to +71C. It's
certainly a common eBay item. It's also what's in a 3805A.
http://www.hparchive.com/Manuals/HP-10811AB-Manual.pdf on page 3

http://morion.com.ru/catalog_pdf/MV89-OCXO.pdf

there are other examples.

Bob

On Dec 16, 2012, at 7:37 PM, Said Jackson saidj...@aol.com wrote:

Bob,

Lastly, don't forget that it's not just the ocxo that's airflow sensitive,
the DAC, filters, amp, and DAC reference all are thermally sensitive and
will be affected by airflow as well.

Bye,
Said

Sent from my iPad

On Dec 16, 2012, at 3:38 PM, Bob Camp li...@rtty.us wrote:

Ok where to start.

Some typical numbers:

A DOCXO likely will be specified at around 0.3 ppb peak to peak over -30 to
+70C. That comes out to 0.003 ppb per degree. A single OCOX likely will be
specified at around 10 ppb peak to peak over -30 to +70C. That's 0.1 ppb
per degree. Yes, there are a number of variations, but those numbers are
not at all crazy. eBay will happy cough up a lot of parts with those sort
of numbers on them.

---

Re: [time-nuts] Z3805A cooling requirements?