[time-nuts] Assistance needed to understand some V_OCXO stability concepts.
Bob kb8tq
kb8tq at n1k.org
Sun Oct 25 16:16:46 UTC 2020
Hi
There are two versions of the 10811, one plugs into the “target” via an edge
connector. If that is the version you have, there are pin(s) that should be used
for the oven ground connection.
Bob
> On Oct 25, 2020, at 7:11 AM, Joe & Gisela Noci <jgnoci at gmail.com> wrote:
>
> Well, spent a good few days undoing a number of my well intentioned
> 'improvements' to the HP OCXO thermal shielding, mounting, etc, in my
> GPSDO...
> I had mounted the osc on 4 plastic standoffs to thermally isolate the osc
> from the aluminium chassis and its heatsink effects.
> I had also made a 20mm thick styrene box, a thermal shield, all round the
> osc.
> All this had two disastrous effects -
> 1. The heater power, electronics power and EFC control voltage ground
> reference to the OSC
> all enter the 'isolated' osc via the coax-connector shields - these are
> press-on connectors, and they are
> quite 'loose' when fitted - they make contact but are easily 'wobbled'.
> Some basic tests using an external DC supply for the heater voltage
> (grounded to the osc case)
> showed a distinct improvement due to the heater supply return ( ground
> lead) now not in series with the other voltage returns via the coax cables
> and connectors.
> 2. Over a 24hour ambient temp variation, the heater current variation was
> quite large, from cool to hot environment -
> also, during warm periods, the heater would come close to almost off. I
> thought this to be bad, as it would not be easy to get rid of heat.
>
> I then dug out the old carcass of the HP5065A to refresh my mind on the
> original mounting structure - the osc was hard mounted, no cooling fans,
> conduction and convection only, with lots of aluminium bulk about!
>
> So, removed all the thermal insulation, hardmounted the osc onto the 2mm
> Aluminium internal chassis base plate, changed the supply voltage to the
> 50mm cooling fan from 12V to 5V
> ( it now creates a just discernible movement of internal air, gently out
> the bottom vents) This cools mainly the rest of the electronics - all the
> 10MHz buffers,
> The signal gen PLL, the DDS signal gen, etc.
> And now the DC returns have a solid return via the osc casing. The heater
> voltage ( across the heater) is now in a more mid-range, and does not
> approach the off-limit.
>
> I let it run for 4 days to settle a little, and did a 12 hour run recording
> the output from the (analogue) TIC.
> Attached is the Adev per TimeLab...will run for a week or so and see what
> develops.
>
> Thanks so far to all the people who have commented and steered my
> frustrations in a better direction!
> Joe
>
>
> On Sun, Oct 18, 2020 at 3:59 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>
>> Hi
>>
>>> On Oct 18, 2020, at 1:49 AM, Joe & Gisela Noci <jgnoci at gmail.com> wrote:
>>>
>>> Hi Bob.
>>> I do appreciate you taking the time to read my lengthy stories and
>> helping
>>> enlighten me!
>>> I am very green with respect to this subject and the underlying physics,
>>> but it remains a fascinating challenge.
>>>
>>> From your comments I realise that I may in fact be inventing issues
>> because
>>> of my lack of experience and a second 'oven' is not the way to think
>> about
>>> this.
>>> I may in fact have built into my design a setup that is causing problems
>> (
>>> although deciding what that problem is , is part of the problem!)
>>> The OCXO is mounted on plastic standoffs, with a shield between it and
>> the
>>> rest of the enclosure to try reduce the influence of the heat from the
>> rest
>>> of the electronics ( doublers, buffers, Synth, DDS, etc).
>>> There is a small fan cooling the rest of the electronics, while the OCXO
>> is
>>> in stagnant air, with 'cooling; only by air contact to the enclosure
>>> aluminium sides.
>>>
>>> This is quite different from the original HP-5061A construction, from
>> which
>>> the OCXO was pulled - the OCXO was hard mounted on the 5061 internal
>>> chassis, no fans, with lots of convection cooling holes
>>> in the 5061 covers, etc. The chassis would also conduct OCXO enclosure
>> heat
>>> away as well.
>>> I think I must go back to the original mechanical concept, as designed by
>>> HP, and not try to be smarter!
>>
>>
>> If you look at a range of HP gear, the OCXO often got mounted in the rear
>> of the
>> device, right next to the big noisy fan. That probably made a lot of sense
>> packaging wise. The vibration from the fan isn’t doing the OCXO any favors
>> in those designs ….
>>
>>
>>> I have a lot to learn..
>>>
>>> If I may ask for clarity on something you said -
>>>
>>> *One would *guess* that the 69C is the turnover of the crystal. The
>> “rated”
>>> uppertemperature of the OCXO would be 10 to 20C below this temperature.
>> *
>>>
>>> I do not quite understand the part in red - 69C is the temp at which the
>>> crystal should be kept, correct? I do not understand the 'rated upper
>>> temp' being 20C below?
>>> Is that the temp of the case, ambient, ??
>>
>> In your typical OCXO spec, the ambient temperature is specified. The
>> assumption
>> is that it is moving air at that temperature. The air is allowed to hit 5
>> of the 6
>> sides of the part ( no air to the mounting surface). Air velocity (and air
>> direction)
>> is rarely defined.
>>
>> The “why?” is simply that this is the way a temperature test chamber
>> works. The
>> parts are all put on a fixture. The group goes in the test chamber. A
>> temperature run
>> is done. The results are analyzed. The parts are sorted out based on the
>> data.
>> Your typical temperature test chamber moves a *lot* of air ….
>>
>> Case temperature on a “typical” OCXO will always be above ambient. How much
>> above depends a lot on the way the insulation was designed.
>>
>> =======
>>
>> Indeed OEM’s would get into issues with temperature. Oddly enough, they
>> seemed
>> to have more issues with TCXO’s ( that don’t heat things up) than with
>> OCXO’s.
>> Thermal design apparently is not easy for anybody.
>>
>>>
>>> Bob, thanks again for your guidance - I don't want to latch onto you and
>>> waste your time with what are probably 'OXCO - 101' experience levels,
>> but
>>> thanks for the help!
>>
>> No problem …. happy to help.
>>
>> Bob
>>
>>>
>>> Thanks again!
>>> Regards
>>> Joe
>>>
>>> On Sun, Oct 18, 2020 at 12:31 AM Bob kb8tq <kb8tq at n1k.org> wrote:
>>>
>>>> Hi
>>>>
>>>> (see below)
>>>>
>>>>> On Oct 17, 2020, at 4:22 PM, Joe & Gisela Noci <jgnoci at gmail.com>
>> wrote:
>>>>>
>>>>> Thanks for your response Bob.
>>>>> In my implementation, the OCXO has two supply inputs -
>>>>> one for the Oscillator, +18V and one for the Oven , +24V. They are both
>>>>> linear regulators, but fed from the same +32V DC unreg source.
>>>>> The EFC voltage consists of two parts, a -7V fixed supply, derived from
>>>> and
>>>>> Analogue devices +10v, 1ppm Voltage reference, and a 0 to +10V from a
>>>>> 16bit DAC.
>>>>> The DAC is an Analogue devices chip, with an internal 2ppm reference.
>>>>> The EFC module ( DAC and references, etc) PCB is in a small enclosure,
>>>>> 30x30x10mm, fitted against the side of the OCXO ( The HP-106 module is
>> a
>>>>> large block - the outer Aluminium housing runs quite warm)
>>>>> The temp variation measured on the DAC chip is typically 1 to
>> 1.5degrees
>>>> C,
>>>>> so the voltage references are reasonably stable.
>>>>
>>>> sounds ok so far.
>>>>
>>>>>
>>>>> What does bother me is the possibility of the increase in heater
>> current,
>>>>> when heating, affecting the DAC output voltage, or rather, affecting
>> the
>>>>> volt drop across the ground feed wire ( the negative
>>>>> leads from PSU to the OCXO). The HP-106 does not have a good -ve
>>>>> supply input in my opinion - there are 4 coax style inputs,
>>>>> two are plus and minus EFC in, one is 5MHz output, and a 'stable' +15v
>>>> out.
>>>>> Then there are three input pins, +18V osc supply, +24V heater, and some
>>>>> other. The ground/-ve supply input is the
>>>>> shield outers of the coax connectors, and so the -ve supply to the DAC
>>>> and
>>>>> the -ve supply to osc and heater share this same -ve lead input...
>>>>> I am looking to re wire the unit to try ensure that all grounds are
>>>>> referenced at a single point somehow - not easy!
>>>>
>>>> I think you will find that the case of the OCXO is also grounded. If you
>>>> return
>>>> each of the grounds involved directly to the case, that should reduce
>> the
>>>> cross
>>>> coupling to the minimum. Indeed you could re-wire the internals of the
>> OCXO
>>>> to go a bit further.
>>>>
>>>>>
>>>>> I sort of understand your statements regarding the implications of an
>>>>> external housing - I suppose all I want to try do is to limit the
>> ambient
>>>>> temp change that the osc case is exposed to
>>>>> by having a second layer. Can't quite get my head around the how
>> though.
>>>>> The OCXO is labeled to run the oven at 69.3deg C - rather hot indeed! I
>>>>> have opened the one end (gently) and
>>>>> fitted a thermistor temp probe into the osc can foam surround, against
>>>> the
>>>>> can - it registers 69.7degC, but I cannot guarantee the HP temp meter
>>>>> calibration!
>>>>
>>>> One would *guess* that the 69C is the turnover of the crystal. The
>> “rated”
>>>> upper
>>>> temperature of the OCXO would be 10 to 20C below this temperature. Put
>>>> another
>>>> way: there is power going into the part even when the oven tries to shut
>>>> off. This
>>>> power still “counts” against temperature rise.
>>>>
>>>>
>>>>> But at that temp, does it make it easier to add a surrounding 'oven'
>>>> since
>>>>> the differential is quite large? Still battle with the concept though -
>>>>> A (wooden ?) enclosure - something that does not conduct heat well?
>> with
>>>> a
>>>>> large airgap tween it and the OCXO, and a fan circulating the air in
>> the
>>>>> gap - bringing in air from outside would cool all down,
>>>>> the extent of which would depend on the temp of the ambient air, and so
>>>>> bring me back to square one..
>>>>
>>>> Well, it sort of gets us back to a very basic question:
>>>>
>>>> If this is a GPSDO *and* the GPS is doing it’s thing … what do we care
>>>> about?
>>>> A transition that takes hours to complete *should* be taken out by the
>>>> GPSDO
>>>> function …. Things that take minutes (or maybe an hour) are what will
>> make
>>>> things messy. Drafts and other transient temperature effects are the
>>>> target here.
>>>>
>>>> Bob
>>>>
>>>>
>>>>>
>>>>> Regards
>>>>> Joe
>>>>>
>>>>>
>>>>> On Sat, Oct 17, 2020 at 6:54 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>>>>>
>>>>>> Hi
>>>>>>
>>>>>> Oven supply sensitivity and oven temperature sensitivity are two
>>>> different
>>>>>> (and
>>>>>> independent) aspects of the oscillator. One magnitude of one parameter
>>>>>> does not
>>>>>> predict the magnitude (or direction) of the other parameter. Indeed
>>>>>> changes in
>>>>>> either voltage or temperature will have an impact, that’s about all
>> you
>>>>>> can be
>>>>>> sure of.
>>>>>>
>>>>>> When you design an OCXO, you have a number of components that are
>>>> sensitive
>>>>>> to voltage and / or temperature. There is no way to put them all at a
>>>>>> single point.
>>>>>> The heat from the heater and heat from the outside will hit different
>>>>>> parts in different
>>>>>> ways. Since they are different distances from the temperature
>> sensor(s)
>>>>>> the control
>>>>>> point will have a different impact on each of them.
>>>>>>
>>>>>> The net result is that you balance the oven gain and set point for
>>>> optimum
>>>>>> temperature
>>>>>> performance. In a modern part temperature runs are done to optimize
>> both
>>>>>> parameters.
>>>>>> The oven is then set to those “correct” values. Any change in set
>> point
>>>> or
>>>>>> gain is
>>>>>> likely to degrade the performance. Gain is impacted by changing the
>>>>>> insulation on
>>>>>> the oven.
>>>>>>
>>>>>> If you wish to do an enclosure, you need some “room” around the part
>> for
>>>>>> air circulation.
>>>>>> The more circulation, the closer you can get to the rated upper limit
>> on
>>>>>> the part. In a
>>>>>> closed box with little moving air, a 20C to 30C “offset” may be needed
>>>> ( =
>>>>>> a 50 C OCXO
>>>>>> might only work to 50 - 30 = 20C. ). With a fan (even a small one) you
>>>>>> could get much
>>>>>> closer to the rated upper limit. Fans add their own problems so that
>> may
>>>>>> be a win / loose
>>>>>> sort of proposition.
>>>>>>
>>>>>> =====
>>>>>>
>>>>>>
>>>>>> Best approach to care and feeding of an OCXO:
>>>>>>
>>>>>> Put it on an independent linear regulator. If oscillator and oven have
>>>>>> separate inputs,
>>>>>> put each on its own regulator.
>>>>>>
>>>>>> Generate the EFC from a voltage reference. Do not use the “other”
>> supply
>>>>>> voltages
>>>>>> to derive the EFC. EFC is much more sensitive than the other pins.
>>>>>>
>>>>>> Leave it on power all the time.
>>>>>>
>>>>>> Keep it loaded with the correct load.
>>>>>>
>>>>>> Buffer the output before it goes anywhere.
>>>>>>
>>>>>> Keep drafts away.
>>>>>>
>>>>>> Keep the temperature as stable as you can.
>>>>>>
>>>>>> Older parts will (likely) be sensitive to pressure and humidity. There
>>>>>> isn’t a lot you
>>>>>> can practically do about this. Going to a newer part that is better
>>>> sealed
>>>>>> / designed
>>>>>> is generally the best alternative. (Yes, there are exceptions to
>>>> this…..)
>>>>>>
>>>>>> =====
>>>>>>
>>>>>> The longer slope in your plot is (likely) aging. It is not uncommon
>> for
>>>>>> older parts
>>>>>> to take a *long* time to stabilize. Stabilization times dimensioned in
>>>>>> months are
>>>>>> not uncommon. I have seen units that have taken > 9 months to settle
>>>> down.
>>>>>>
>>>>>> Bob
>>>>>>
>>>>>>
>>>>>>
>>>>>>> On Oct 17, 2020, at 4:54 AM, Joe & Gisela Noci <jgnoci at gmail.com>
>>>> wrote:
>>>>>>>
>>>>>>> Hi to all,
>>>>>>> Still persevering with my GPSDO - this stuff is very addictive...
>>>>>>> I may be able to have a loan Rubidium reference for a few weeks which
>>>>>> will
>>>>>>> assist me with comparative measurements - I hope!
>>>>>>>
>>>>>>> In the meantime, the effects of ambient temp changes are very evident
>>>> in
>>>>>>> the change of oven control voltage, and therefore the EFC voltage as
>>>>>> well -
>>>>>>> Exactly what the effect is on frequency remains to be seen once I
>> have
>>>>>> the
>>>>>>> above reference.
>>>>>>> However, I would in any case like to try improve on this situation.
>> The
>>>>>> OCXO
>>>>>>> ( HP_00105-6013) is covered in a 25mm thick polystyrene 'box' inside
>>>> the
>>>>>>> enclosure of the entire unit. The unit external shell is 2mm
>> aluminium,
>>>>>> and
>>>>>>> so does radiate internal heat, etc.
>>>>>>> I would like to try a sort of external oven arrangement - remove the
>>>>>> OCXO
>>>>>>> from the system unit enclosure, and fit it into a dedicated enclosure
>>>>>> that
>>>>>>> forms
>>>>>>> a hopefully better temp shield around the OCXO, and make this housing
>>>>>>> internally temp controlled.
>>>>>>> The temp control would not have to be very accurate, maybe a few (2?)
>>>>>>> degrees C, all in an effort to improve on the ambient temp effects I
>> am
>>>>>>> seeing.
>>>>>>> My lab ambient changes from 15 degC to 26degC over a winter 25hour
>>>> period
>>>>>>> typically, and does reach 28degC in summer..
>>>>>>>
>>>>>>> Has anyone reading this had any experience in designing something
>> like
>>>>>>> this? It is not so simple as there not a great temp differential to
>>>> play
>>>>>>> with.
>>>>>>> I guess the second 'oven' would need not only a heating capability,
>> but
>>>>>>> cooling as well - to try stabilize at maybe 30 degC internally?
>>>>>>>
>>>>>>> I have dug in the archives, and a lot of googling took place, but
>> this
>>>>>> sort
>>>>>>> of info is scarce!
>>>>>>>
>>>>>>> An annotated screen shot shows the daily temp variation effects on
>> the
>>>>>> oven
>>>>>>> control voltage, and on the DAC control voltage.
>>>>>>> Scale is in 10's of seconds horizontally. Oven volts are actually the
>>>>>> volts
>>>>>>> across the control transistor of the HP oven , so high volts = less
>>>>>> heating
>>>>>>> DAC volts are in millivolts
>>>>>>> The rising trend in oven volts ( reduced heating) over the
>> 48something
>>>>>>> hour period shows the gentle increase in daily ambient temps as we
>> are
>>>>>>> warming up here.
>>>>>>> The DAC control voltage is synced to the oven control voltage - as
>> the
>>>>>> oven
>>>>>>> voltage increases so does the DAC voltage. I have not implemented a
>>>>>> means
>>>>>>> of actually measuring the oven temp, but that may be needed - to be
>>>> sure
>>>>>>> that the temp is in fact being controlled properly - as I have no
>> idea
>>>> of
>>>>>>> the actual temp change for that oven voltage change. I also hope that
>>>>>> there
>>>>>>> are no supply power return path issues -
>>>>>>> that the DAC voltage is perhaps affected by the change in oven
>> current
>>>>>> and
>>>>>>> so the system tries to compensate...
>>>>>>>
>>>>>>> Also, a disturbing trend in the DAC voltage - the voltage is going
>> more
>>>>>>> negative all the time, even though the oven volts are in a positive
>>>>>> trend -
>>>>>>> ie, the oven is 'cooling' more with increasing ambient, which should
>>>>>>> make the DAC volts trend increase at the same time, but it is
>> trending
>>>>>> more
>>>>>>> negative - I wonder if this is not an issue of crystal aging...
>>>>>>>
>>>>>>> The attached screenshot is around 48 hours long, but a 2 week long
>>>>>> capture
>>>>>>> at 10second rate has the DAC voltage decreasing from 5250mV to the
>>>>>> present
>>>>>>> 4900mV
>>>>>>> Need to measure oven temp!
>>>>>>>
>>>>>>> MANY things to dig into!
>>>>>>>
>>>>>>> Regards
>>>>>>> Joe
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Fri, Oct 2, 2020 at 5:35 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>>>>>>>
>>>>>>>> Hi
>>>>>>>>
>>>>>>>> On an oscillator that is 50 years old, there likely has been some
>>>> aging
>>>>>> of
>>>>>>>> the crystal
>>>>>>>> and other components. As you tune the crystal back onto frequency,
>> you
>>>>>> can
>>>>>>>> easily
>>>>>>>> impact the EFC sensitivity. On *any* older device, “measure” is very
>>>>>> much
>>>>>>>> the right
>>>>>>>> way to do it.
>>>>>>>>
>>>>>>>> Bob
>>>>>>>>
>>>>>>>>> On Oct 2, 2020, at 7:44 AM, Joe & Gisela Noci <jgnoci at gmail.com>
>>>>>> wrote:
>>>>>>>>>
>>>>>>>>> Hello Tom.
>>>>>>>>> Thanks for your info.
>>>>>>>>>
>>>>>>>>> My oscillator comes from an HP-5061a, which I obtained from a
>> company
>>>>>> as
>>>>>>>>> the tube was dead.
>>>>>>>>> The log book indicates a start date of 1971, so yes, not a
>> youngster!
>>>>>>>>> I have the full set of original manuals for this 5061A , but the
>>>>>>>> oscillator
>>>>>>>>> specs are not detailed to the KV level, nor is the actual voltage
>>>> level
>>>>>>>>> range of EFC indicated in the manual.
>>>>>>>>> The full circuits are there, etc.
>>>>>>>>> In the 5061A , the EFC was a +ve voltage from an accurate
>> reference,
>>>>>> via
>>>>>>>> a
>>>>>>>>> front panel multiturn pot, onto the +EFC input, and then the loop
>>>>>> control
>>>>>>>>> voltage from a op-amp/hybrid, which is fed from a split 30volt
>>>> supply.
>>>>>>>>> So it was not possible to discover what range the control voltage
>> out
>>>>>> of
>>>>>>>>> the op amp covered ( not in the circuit descriptions) . I finally
>>>>>>>>> discovered in the calibration descriptions that the front panel pot
>>>> had
>>>>>>>> to
>>>>>>>>> be at midrange ( -7.5v) and the coarse
>>>>>>>>> control trimcap in the OCXO adjusted to set the control voltage
>> (+EFC
>>>>>>>>> voltage) to +5V....
>>>>>>>>>
>>>>>>>>> Thanks again!
>>>>>>>>>
>>>>>>>>> I will persevere!
>>>>>>>>>
>>>>>>>>> Kind Regards
>>>>>>>>> Joe
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Fri, Oct 2, 2020 at 12:41 PM Tom Van Baak <tvb at leapsecond.com>
>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Joe,
>>>>>>>>>>
>>>>>>>>>> The 00105 oscillator was used in early hp 105 quartz frequency
>>>>>>>>>> standards. So the specifications, theory of operation, photos and
>>>>>>>>>> schematics for the 00105 "brick" oscillator are all in the hp 105
>>>>>> op/svc
>>>>>>>>>> manual (April 1968).
>>>>>>>>>>
>>>>>>>>>> There are two copies on Didier's site. Go to
>>>>>>>>>> http://www.ko4bb.com/manuals/ and type 105ab into the search box.
>>>>>>>>>>
>>>>>>>>>> The EFC+ and EFC- inputs are a little different from a modern
>> OCXO.
>>>>>> The
>>>>>>>>>> hp105 provides a rear EFC input that works from -5 V to +5 V and
>>>>>> changes
>>>>>>>>>> df/f by "greater than 4e-8" over that range. [1] So that would be
>>>> 4e9
>>>>>> /
>>>>>>>>>> V which at 5 MHz is 0.02 Hz / V. Check the schematics for how they
>>>>>>>>>> implement it; the manual provides all the details. It may be an
>>>>>> example
>>>>>>>>>> for your GPSDO. Your 0.033 number sounds ok to me.
>>>>>>>>>>
>>>>>>>>>> In general, as you have done, it's always best to measure rather
>>>> than
>>>>>>>>>> read the manual, especially since the manual uses the word
>> "greater
>>>>>>>>>> than", and also since some of these 00105 oscillators are
>>>> approaching
>>>>>> 50
>>>>>>>>>> years old. If you have a frequency counter it should be simple to
>>>>>>>>>> measure the frequency during a voltage sweep, make a plot, and
>>>>>> determine
>>>>>>>>>> the range, the slope, and also the linearity. The nice thing about
>>>> EFC
>>>>>>>>>> experiments is that you don't even have to wait for the oscillator
>>>> to
>>>>>>>>>> fully stabilize.
>>>>>>>>>>
>>>>>>>>>> /tvb
>>>>>>>>>>
>>>>>>>>>> [1] EFC paragraph from page 2-4 of hp 105 manual (02479-1)
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On 10/1/2020 11:53 PM, Joe & Gisela Noci wrote:
>>>>>>>>>>> Jim,
>>>>>>>>>>> some further info -
>>>>>>>>>>> The OCXO I use - HP_00105-6013 - does not have a lot of info
>>>>>> available
>>>>>>>>>> - I
>>>>>>>>>>> have searched all over! I have found no definitive info on its
>> KV,
>>>>>> etc,
>>>>>>>>>> so
>>>>>>>>>>> had to determine it myself.
>>>>>>>>>>>
>>>>>>>>>>> This I did as follows ( the complexity of my process was to try
>>>>>>>> 'really'
>>>>>>>>>>> know if it is correct, and if the OCXO behaves according to the
>>>>>> correct
>>>>>>>>>>> Physics!)
>>>>>>>>>>>
>>>>>>>>>>> The two jpegs,
>>>>>>>>>>> *KV determination @5V and 6V.jpg* and *KV determination @9V and
>>>>>>>> 10V.jpg*
>>>>>>>>>>> show the phase detector wrap around during HOLD mode, with the
>> DAC
>>>>>>>> output
>>>>>>>>>>> set to specific voltages.
>>>>>>>>>>>
>>>>>>>>>>> For these tests the OCXO was left running for 24hours to warm up
>>>> and
>>>>>>>>>>> stabilize as best it could.
>>>>>>>>>>>
>>>>>>>>>>> The 9V_10V and 5V_6V tests differ in the following:
>>>>>>>>>>>
>>>>>>>>>>> * For the 9V_10V test:*
>>>>>>>>>>>
>>>>>>>>>>> The -EFC Voltage was set to -10V
>>>>>>>>>>> The +EFC DAC voltage was first set to 8V and the phase detector
>>>>>>>> monitored
>>>>>>>>>>> on a 'scope. The coarse adjust trim cap in the OCXO was then
>>>> adjusted
>>>>>>>> so
>>>>>>>>>>> that the phase detector voltage was close to 1volt and 'not'
>>>>>> drifting.
>>>>>>>>>> This
>>>>>>>>>>> was monitored and adjusted over a 3 hour period to verify
>>>> reasonable
>>>>>>>>>>> stability.
>>>>>>>>>>>
>>>>>>>>>>> Then the detector voltage was recorded with DAC set to 9V.
>>>>>>>>>>> Then the DAC voltage was set to +10V and the detector voltage
>>>>>> recorded
>>>>>>>>>>> again.
>>>>>>>>>>> The phase detector wrap around time were 620sec @ 9V and 300sec @
>>>> 10V
>>>>>>>>>>>
>>>>>>>>>>> I believe this equates to -
>>>>>>>>>>> @9V t=620sec so 10/620 = 0.0162Hz
>>>>>>>>>>> @10V t=300sec so 10/300 = 0.0333Hz
>>>>>>>>>>> *So KV = 0.0333-0.01612 = 0.017 Hz/V*
>>>>>>>>>>>
>>>>>>>>>>> * For the 5V_6V Test:*
>>>>>>>>>>>
>>>>>>>>>>> The -EFC voltage was set to -7V.
>>>>>>>>>>> With the DAC voltage @+4V first, the OCXO coarse adjust was set
>> so
>>>>>> the
>>>>>>>>>>> phase detector voltage was stable.
>>>>>>>>>>> Then the DAC was set to +5V, which gave a wrap-around time of t=
>>>>>> 550sec
>>>>>>>>>>> Then with the DAC V= +6V, t=200sec.
>>>>>>>>>>> *This gives a KV of 0.032 Hz/V*
>>>>>>>>>>>
>>>>>>>>>>> This all makes sense since the varicap is operating on a
>> different
>>>>>> part
>>>>>>>>>>> capacitance curve slope - at the lower voltages the capacitance
>> is
>>>>>>>>>> greater,
>>>>>>>>>>> so the delta_V effect will be greater.
>>>>>>>>>>>
>>>>>>>>>>> This verifies that the KV values are valid and sensible.
>>>>>>>>>>>
>>>>>>>>>>> I made use of the 0.033Hz/V settings, as that is what my loop
>> gains
>>>>>> are
>>>>>>>>>>> calculated for.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
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>>>>>>>>>>
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>>>>>>>>
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>>>>>>> <OCXO Oven trend.jpg>_______________________________________________
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